- Email: [email protected]
Physical activity, functional limitations, and the risk of fall-related fractures in community-dwelling elderly
ELSEVIER
Physical Activity, Functional Limitations, and the Risk of FallcRelated Fractures in Community-Dwelling Elderly JUDY A. STEVENS, MS, MPH, KENNETH E. POWELL, MD, MPH, SUZANNE M. SMITH, MD, MPH, PHYLLIS A. WINGO, PHD, MS, AND RICHARD W. SATTIN, MD
This case-control study examines the association of vigorous and mild physical activity with fallrelated fractures in a community-dwelling population age 65 and older in South Florida. Vigorous physical activity was defined as exercising, doing heavy housecleaning, or other hard labor three or more times per week in the month prior to the index date; mild physical uctioritywas dejined as the number of hours per day subjects reported spending on their feet. A case was any subject who sustained a fall-reiated fracture (ED-9CM-800 through ED-9CM-829) over a 21 -month period (n = 471). Controls werea 10% randomsampleselectedfrom the Health Care Financing Administration Medicare files (n = 712). The presence of any limitation in activities of daily living (ADL) significantly modified the effect of vigorous physical activity. Physically active subjects with no limitations (ADL = 0) were lesslikely to sustain a fall-related fracture than were inactive subjects, with an adjusted oddsratio (aOR) of0.6, (0.5-0.8 95% CI), and active subjectswith any limitation (ADL 2 I) had an aOR of 3.2 (1.1-9.8 95% CI) . Limiting this analysis to 159 hip fracture cases producedsimilar results. Mild physical activity was not associated with fracture. Theseresultssuggest that vigorous physical activity is associatedwith a lower fracture risk amongelderly personswho huue no limitations in ADL and with a higher risk among those with any limitations. 0 1997 by Elsevier
Science, Inc. KEY WORDS:
Ann Epidemiol 1997;7:54-61. Elderly, falls, fractures, physical activity, exercise, activities of daily living.
INTRODUCTION
Fractures due to falls are a significant problem among the elderly (1). The most frequent fractures involve the femoral neck, humerus, vertebra, radius, ulna, and bones of the pelvis, hand, and ankle (2), and most result from falls (3-5). In the United States, the morbidity and mortality associated with fractures can be expected to increase as the population ages.
Three components contribute to the risk of fractures: lack of bone strength, the risk of falling, and ineffective protective neuromuscular reactions when a fall occurs (4, 6, 7). Physical activity may reduce the risk of fractures by modifying all three components: preventing or reducing bone loss at all ages (g-15), increasing muscular strength,
From the National Center for Injury Prevention and Control (J.A.S., K.E.P., R.W.S.) and the Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA (S.M.S.); and the American Cancer Society, Atlanta, GA (P.A.W.). Address reprint requests to Judy A. Stevens, CDC/NCIPC, 4770 Buford Highway, Mailstop K63, Chamblee, GA 30341. Received November 10, 1995; revised July 3, 1996; accepted July 26, 1996. 0 1997 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
and improving balance (16-18), flexibility, coordination, and reaction time (19, 20). Although a number of recent studies have demonstrated a reduction in the risk of hip fracture with increasing activity, these studies used disparate definitions of physical activity, such as lists of various activities (15,21,22) and frequencies of walking and standing (23-25). The studies also included subjects in differing age ranges (15, 24) and failed to adjust adequately for potential confounders such as age (23), alcohol, and estrogen replacement therapy (ERT) (22). The purpose of this study was to address the following questions, adjusting for potential confounders. First, is current vigorous physical activity associated with a lower risk of fall-related fractures in men and women aged 65 and older? Second, is mild physical activity also associated with a lower risk of fall-related fractures in men and women aged 65 and older?
METHODS
The data for the current analysis were derived from the Study to Assess Falls among the Elderly (SAFE), which is described in detail elsewhere (26, 27). Briefly, this was a population-based, case-control study of fall-related injuries 1047s2797/97/$17.00 PII S1047-2797(96)00110-X
:;it i’,‘llbt‘i ai PHYSICAL ACTIVITY
among community-dwelling people aged 65 and older in a geographically defined area of Miami Beach, Florida. Potential caseswere ascertained through an active, population-based surveillance system that obtained data from South Miami Beach Fire Rescue summary reports, Dade County medical examiner investigation reports, and six study area hospital emergency department and inpatient medical records. These hospitals provided treatment for all serious injury casesthat occurred within the study area (27). Demographic and medical information were abstracted from medical records for inclusion in the surveillance system. A nosologist coded the anatomic nature of the injury (N-code) and the external cause of the fall injury (E-code) according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) (28), and the data were entered into a microcomputer data file. Because 87% of fall-related fractures occur in and around the home (29), caseswere defined as any study area resident aged 65 or older who received treatment for a newly diagnosed fracture (ICD-9CM-800 through ICD-9CM-829) due to an unintentional fall in or about their home (E849.0) that occurred between November 20, 1986, through August 31, 1988. Control subjects were randomly selected and comprised 10% of the population-based Health Care Financing Administration Medicare files of all persons aged 65 or older who resided in the study area in the period during which the caseswere diagnosed. Controls were frequency matched to the expected age distribution of casesbased on the results from a pilot study.
Data Collection Trained interviewers administered the questionnaire in English or Spanish (Cuban dialect), usually in the respondent’s home. Most information was self-reported and included data on personal and demographic characteristics including birth date, height, weight, physical activity (currently and at age 30), activities of daily living (ADL), postmenopausal estrogen use, and mental status. Recall was facilitated by using a calendar to identify periods and dates, and demonstration cards were used for questions about race, religion, marital status, and frequencies of occurrence. The index date for cases was the injury date. To make the titne from selection to interview approximately the same for cases and controls, the index date for controls was 1 month prior to their selection date. The reference period was the month before the index date. Because interviews were conducted in respondents’ homes and some fractures can require extended hospitalization, the interview deadline was 6 months after the index date.
55
AND FALL-REL/ITET, Fii,\IT1-!JREC
Definitions of Vigorous Physical Activity, Activity, and ADL
Mild Physical
Respondents who engaged in vigorous physical activity were those who answered “yes” to the question, “[Before the reference period] did you do exercise, heavy housecleaning, or other hard labor three or more times per week?” We included “heavy housecleaning” because women comprised approximately 60% of the over-65 population in the study area. Studies have shown that women spend more time and expend a greater amount of energy in household activities than do men (30). We chose the phrase “4lther hard labor” so that respondents would include additional activities that were not specifically mentioned in the question. The definition of mild physical activity was based on the only available relevant question, “Before [the reference period], about how many hours per day did you spend on your teet?” (categorized as none, up to 1, Z-4, 5-7, and 8 or more). Vigorous and mild physical activity were positively correlated (Spearman rank correlation = 0.32, P = 0.0001) alld showed good concordance; 61.3% of respondents who engaged in vigorous physical activity also reported spending 5 or more hours per day on their feet; 70.4% of those who did not engage in vigorous activity spent less than 5 hours :sday on their feet. Each subject’s level of dependence WASassessedusing a simplified version of the Katz index of XDL ( 7 1). Selfreported dependence (on a scale of 0 to 5 9 was defmed as requiring help in carrying out five basic dady activities: eating, bathing, dressing, transferring, ArId toileting. An ADL score of 0 meant that the respondent was independent in all five activities; a score of 1 or higher meant that the respondent was dependent in the ccm~a~~~-~lingnumher of activities. Mental Competency Assessment The respondent’s mental competency was :issessedbased on answers to the 21-question mental statkfs section of the questionnaire. Because cognitive impairment has been associated with a higher risk of falling (6), we computed a mental status score based on a subset of 16 questions and derived from the Mini-Mental State Exam developed by Folstein et al. (32). The 16 questions corresponded to the original Folstein items for Orientation, Registration, and Recall and had been validated for persons vged 65 and older from the Baltimore Survey of the Epidemiologic Catchment Area study (33). This study categorized an individual with a mental status score of I2 or less as cognitively impaired. Surrogate Information A proxy respondent was interviewed if an eligible individual was physically incapable of completing the questionnaire or mentally incompetent based on an initial screening at the beginning of the interview. Although there were specified hierarchical rules for selecting surrogates, beginning with a
56
Stevens et al. PHYSICAL ACTIVITY
spouse, a relative, then a friend or neighbor, one possible surrogate was available. Statistical
AEI’ Vol. 7, No. 1 Januq 1997. 54-61
AND FALL-RELATED FRACTURES
usually only
Analysis
In the univariate analyses, we calculated the crude odds ratios (cOR) and 95% confidence intervals (CI) for the dichotomous exposure variables defined and evaluated mild physical activity as a categorical variable using a chi-square test for trend (34). We used the Breslow-Day test for homogeneity (35) to assess interaction and the Mantel-Haenszel procedure (36) to adjust for the effects of potential confounders. We used unconditional logistic regression to estimate adjusted odds ratios (aORs) and 95% CI, simultaneously adjusting for potential confounders. Age, sex, ADL, exercise at age 30, ERT (women), Quetelet index, current calcium intake, mental status score, and whether or not physical activity data were supplied by a surrogate were evaluated as potential confounders. Current smoking and alcohol use were not found to be associated with fracture risk in this population (37). The full logistic model consisted of current activity, age, sex, activity at age 30, estrogen use (women only), mental status score, Quetelet index, and whether or not physical activity data were supplied by a surrogate. To develop the final model, we eliminated one variable at a time, selecting the variable with the highest nonsignificant P value. A covariate was considered a confounder and was retained in the model if removing it altered the OR for physical activity by 10% or more. RESULTS We excluded 20 cases and 15 controls who reported that they used a wheelchair exclusively before their injury (or whose wheelchair use was unknown) and 6 cases and 4 controls who did not provide meaningful information about physical activity. After exclusions, the response rate was 471/717 (65.7%) for cases and 712/1060 (67.0%) for controls. Reasons for nonparticipation included refusal (7.9% vs. 19.6%), death (9.9O/, vs. 1.6%), an inability to be located (3.3% vs. 5.7%), having moved outside the study area (8.0% vs. 2.6%), and other reasons (5.2% vs. 3.4%) for cases and controls, respectively. The average time from index date to interview was 2.6 months for cases and 1.9 months for controls. Four hundred seventy-one cases reported 523 fractures; 49 cases sustained multiple fractures at the time of their fall (Table 1). The hip ( net k o f f emur) was the most common fracture site. Table 2 presents selected sociodemographic characteristics of cases and controls. The average ages of cases and controls. The average ages of cases and controls were not significantly different (P > 0.05) when stratified by sex. Approximately 16% of cases and 26% of controls were of
TABLE 1. Distribution of fall-related 471 case subjects age 65 and older
fractures
Fracture site
n
(%I)
160 78 71 64 40 25 24 19 10 9 8 7 3 3 2 523
30.7 14.9 13.6 12.1 7.7 4.8 4.6 3.7 1.9 1.7 1.5 1.3 0.6 0.6 0.4 100.0
Neck of femur Humerus Radius/ulna Ribs, sternum Spine Pelvis Bones of the hand Skull Other parts of femur Ankle Tibia/fibula Foot Clavicle Patella Scapula Total
sustained by
* Forty-six casessustainedtwo fractures; three casessustainedthree fractures.
Hispanic origin; 98% of both cases and controls were white. Physical fraility, defined as impaired strength, mobility, balance, and endurance, appeared to be more prevalent among cases than controls. Compared with controls, cases tended to have a lower body mass index (33% vs. 24% in the lowest quartile of Quetelet index distribution), not participate in vigorous activity (72% vs. 63%), have a functional limitation (ADL 3 1; 18% vs. 12%), have a low mental status score (21% vs. ll%), and have activity data reported by a surrogate (12% vs. 5%). Most cases and controls did not smoke or drink. Respondents with physical activity information supplied by a surrogate differed from those with self-reported data (data not shown). They tended to be older, live in a nursing home at the time of their interview, not have completed high school, not smoke or drink, and have a lower Quetelet index. Among the cases, those with surrogate data were more apt to be male, under 85, and married. Among the controls, those with surrogate data were more likely to be female, over 85, and widowed. Cases and controls reported a similar number of chronic diseases. Vigorous activity was associated with an overall 30% decreased risk of fracture (cOR = 0.7,0.5-0.8 95% CI). In contrast, reported time spent on feet was not associated with fracture risk (Mantel-Haenszel summary OR = 1.08, 0.86-1.4 95% CI), and there was no evidence of a trend of lower fracture risk with increasing time spent on feet (P = 0.30). The majority of the 457 cases and 708 controls with ADL scores reported no limitations. Only 39 cases (9%) and 40 controls (6%) reported needing help with a single activity (ADL = 1); only 47 cases (10%) and 40 controls (6%) had ADL scores of 2 to 5. Among those with ADL
AEP Vol. 7, IL’o. 1 lantuq 1997: 54-61
Stw?ns et dl. AND FALL-RELATED FRACTURES
PHYSICAL ACTIVITY
TABLE 2. Selected characteristics of fracture casesand controls”
TABLE 2. continued Cases
CZXS
n=471
CtES
%
n = 712
%
103 368
21.9 78.1
181 531
25.4 74.6
0.16
AS 65-74 75-84 2 Rj
75 231 165
15.9 49. I 35.1
306 331 235
20.5 46.5 33.0
0.14
Race Whttr Black Other Unknown
463 2 0 6
98.3 0.4 0.0 1.3
699 3 5 5
98.2 0.4 0.7 0.7
0.23
Ethnicity Htspanic Non-Hispanic Unknown
77 389 5
16.3 82.6 1.1
186 521 5
26.1 73.2 0.7
0.0004
Education <3 9-l I 12 2 I3 Unknuwn
152 71 163 46 39
32.3 15.1 34.6 9.8 8.3
291 87 223 65 46
40.9 12.2 31.2 9.1 6.5
0.07
379 132
72.0 2X.0
446 266
62.6 37.4
0.001
6 47 207 98 65 48
1.5 10.0 43.9 20.8 13.8 10.2
6 70 324 174 112 26
0.8 9.8 45.5 24.4 15.7 3.7
0.0004
373 84 14
79.2 17.8 3.0
624 84 4
87.6 11.8 0.6
o.OQoo4
101 G2 8
21.4 76.9 I.7
80 626 6
11.2 87.9 0.8
< 0.00001
47 87 296
10.0 18.5 62.9
48 187 408
6.7 26.3 57.3
0.012
64 5
9.0 0.7
P value
Sex
Male Female
Vigorous activity NC1 Yes Hours/day spent on feet NCW I? Unknown Mariral status Ncwr married Married W1d0wed Separated :)I divorced linkmxvu Smoktng status Ncvcr smoked FOITMX mokrr (:rirrcnt imoker Unknown
38 3 2Y7
63.9
119
27.1
43 12
7.3 17
57
0.46
I.,
(continued)
Alcohol use (drink&k) None
--____
chses
‘Xl
n=471
Y/o
n = 712
369 32 27 29 14
78.3 6.8 5.7 6.2 3.0
515 72 ih ii) it,
71.3 10.1 79 ;.o i.7
0.13
154 198 74 9.5
32.7 42.0 15.7 9.6
lb7 334 I62 49
1’3.5 46.9 z.T.7 t>.‘)
O.ooo2
417 54
88.5 11.5
675 37
94.8 5.2
0.0#07
-----
P value
scores equal to or greater than 1, a higher percentage of cases than controls reported needing help for each of the five activities. The largest proportion (26% of cases and 20% of controls) needed help bathing; 19% af cases and 15% of controls needed help getting in or out of a bed or chair; 16% of cases and 12% of controls needed help dressing; 12% of cases and 7% of controls needed help going to the bathroom or using the toilet; less than 4% of either cases or controls reported needing help eating. Because of the small proportion of cases and controls with ADL scores greater than 1, it was necessary to dichotomize this variable. After stratifying by ADL score (0, 3 1%; Table 3), we observed a significant interaction between the presence of any limitation and current vigorous activity (P = 0.001). There was no interaction between the presence of any limitation and mild physical activity (ADL = 0, cOR = 0.8; ADL 2 1, cOR = 1.2, P =: Q.48). Vigorous physical activity was associated with a lower risk among respondents with an ADL score of zero (cOR = 0.6), but with a higher risk among those with an ADL score equal to or greater than 1 (cOR = 2.6). The stratum-specific ORs were not significantly different depending on whether the data were supplied by the respondent or 3 surrogate. Using unconditional logistic regression to adjust simultaneously for confounding (Table 4), the aOR for respondents with an ADL score of zero was 0.6 (0.4-J.8 95% CI); the aOR for respondents with an ADL score equal to or greater than 1 was 3.2 (1.1-9.8 95% CI). When this analysis was restricted to women and adjusted for ERT (ever/never), the point estimate for women with no limitations became 0.5 ([email protected],95% CI), and the aOR for women with any limitation increased to 5.7 (1. S-25.0 95% CI). Lirnitmg the analv-
Stevens et al. PHYSICAL ACTIVITY
58
TABLE
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AND FALL-RELATED FRACTURES
3. Crude odds ratios (cOR)
and 95% CI between
vigorous
physical
activity,
mild activity, ADL 2 1
ADL = 0
Vigorous activity YES No Mild activity Yes NO
and risk of fracture,
stratified
Cases
Controls
cOR
95% CI
CSSS
Controls
cOR
95% Cl
P-value for heterogeneity
110 263
256 368
0.6
(0.4-0.8)
18 66
8 76
2.6
(1.1-6.2)
0.001”
144 193
271 332
0.9
(0.7-1.2)
15 62
13 67
1.2
(0.5-2.8)
0.48b NS
u& = 10.1. bx:# = 0.5.
sis to 33 men and 126 women who sustained a hip fracture resulted in very similar aORs. Among people with an ADL score of zero, the aOR for hip fracture was 0.6 (0.4-0.9 95% CI); among people with a higher ADL score, the aOR was 4.1 (1.3-12.9 95% CI).
DISCUSSION Overall, vigorous physical activity in this noninstitutionalized elderly population was associated with a lower risk of a fall in the home resulting in a serious fracture, a finding consistent with results from previous studies (17, 20, 38). However, among the subgroup of elderly persons with any limitations in ADL, vigorous activity was associated with a higher risk of serious fracture. No prior studies have reported a differential effect on vigorous activity on the risk of fracture among subgroups of the elderly, a finding that has important implications because exercise increasingly is recommended as a way to improve the quality of life and general health of older persons. Although we observed no risk differences between
4. Adjusted odds ratios (aOR)” for the association between vigorous physical activity and risk of fracture, stratified bv (ADL score TABLE
ADL 5 0
ADL = 0
Vigorous activity Female Age 75-84 285 Low mental status score Quetelet index, Lowest 25% Highest 25%
aOR
95% CI
aOR
95% Cl
0.6 1.3
(0.4-0.8) (0.9-1.8)
3.2 0.6
(1.1-9.8) (0.2-1.5)
1.2 1.3
(0.9-1.6) (0.8-2.1)
0.5 0.3
(0.2-1.2) (0.1-1.0)
2.0
(1.3-3.3)
1.5
(0.7-3.3)
1.4 0.9
(1.0-1.9) (0.6-1.3)
1.5 0.3
(0.7-3.5) (0.1-0.8)
‘Odds ratio adjustedfor sex (M/F), age (65-74, 75-84, 3 85), mental status SCOW (S 12, > 12), and Quetelet index (lowest 25%, middle 50%, highest 25%).
those with an ADL score of 1 and those with an ADL score greater than 1, we had relatively few respondents in the latter category. Moreover, ADL score is a crude measure for a wide range of functional limitations. Research is needed to refine the relationships among physical activity, ADL, and falls. This is the first population-based case-control study of fractures due to falls in a geographically defined, noninstitutionalized elderly population. Cases were ascertained through an active population-based surveillance system that used four sources (Fire Rescue, emergency departments, inpatient hospital records, and Dade County medical examiner reports) to identify serious fractures that occurred in the study area. Outcomes were documented using medical records. We consider case ascertainment to be virtually complete for serious fractures. The distribution of serious fractures in this study was similar to that in a comparable population of Tennessee Medicaid enrollees aged 65 and older (which included fractures treated in hospitals and doctor’s offices) (29). However, we observed smaller percentages for fractures of the skull, ankle, tibia/fibula, and foot. Because we could not ascertain the number of fractures that may have been treated in a physician’s office, our findings may not apply to less serious fractures. Although the epidemiology for various fractures differs (38, 39), vigorous physical activity appears to reduce the risk of many fall-related fractures. When this analysis was repeated using 159 hip fracture cases (126 women and 33 men), the ORs were very similar to those seen for all fractures combined. Some of the limitations of this study should be noted. First, the study population in South Miami Beach may not be representative of other community-dwelling elderly populations, which could limit the generalizability of these findings. Second, although the study achieved an overall participation rate of about 67%, comparable to that in similar studies (15, 24, 40, 41), the possibility of selection bias exists for both cases and controls. However, we think that it is un-
PHYSICAL ACTIVITY
likely to account for our findings because the more likely biases would have shifted the point estimate toward the null value. Cases were more likely to have died than controls and to have data reported by a surrogate. This suggests that interviewed caseswere healthier and more likely to be physically active than noninterviewed cases. If the participating caseswere at lower risk for a fall-related fracture than nonparticipants, the point estimate would be biased toward the null value, leading to an underestimate of risk. In addition, controls were harder to locate and more likely to refuse being interviewed than cases. No additional information was available about nonparticipant controls. These controls may have been busier and engaged in more activities outside their homes than participating controls, suggesting that they may have been healthier. If interviewed controls were less healthy and less active than nonparticipants, the ORs would be biased toward the null value and would be conservative estimates. Third, participants with ADL scores of 1 or above may have responded differently from participants without functional limitations to the question about “exercise, heavy housecleaning, or other hard labor.” Some may have considered everyday activities to be vigorous. If so, the true association between vigorous activity and fall-related fractures would be slightly lower than our estimate. A fourth limitation is the classification of physical activity levels among this group of elderly cases and controls. We classified subjects’ participation in vigorous and mild activity based on their response to a single question for each. Cases and controls were considered to be vigorously active if they indicated that in the month before the index date they had done “exercise, heavy housecleaning, or other hard labor three or more times per week.” We used the term hard labor so that respondents would include activities that they might not consider to be exercise. We attempted to minimize recall bias by asking about recent physical activity. Few questionnaires that assessphysical activity have been evaluated among the elderly. However, at least two have shown reasonable reliability and validity among adults 63 to 80 and 60 to 86 years of age, especially for more vigorous activities (42,43). In addition, among adults 60 to 69 years of age in the Lipid Research Clinics Prevalence Study, selfreported responses to two questions about vigorous activity, similar to the one question in the SAFE questionnaire, correlated with physiologic measures of fitness (44). Therefore, although firmer evidence of validity would be desirable, reported information about participation in vigorous physical activity appears to be reasonably accurate for both elderly subjects and younger adults (45). Of greater concern is our measurement of “mild)’ activity. Our study is consistent with others, which generally have found that vigorous activity is associated with a lower risk of hip fractures due to falls (15, 21, 22, 24). It is less clear whether light to moderate activity in the elderly also de-
:;tt,b,erlset d. AND FALL-RELATER Fli \(7-UREc
59
creasesrisk. Based on a single question, we did not find that the number of hours spent on one’s feet was associated with the risk of fracture, regardless of ADL score. Our results differ somewhat from three previous hip fracture studies that specifically examined the influence of standing (25), walking (3), and standing, walking speed, and walking time (24). In a large prospective study, Cummings et al. (25) observed that women who spent less than 4 hours a day on their feet had a 70% higher risk of fracture than women who spent more time on their feet. Among women in Hong Kong, Lau et al. (3) reported a significantly increased risk associated with walking less often than once a day either uphill or carrying a load. Cooper et al. (24) reported that fracture risk increased with shorter standing times and slower walking speeds. They did not observe an association between reduced walking time and increased risk. but, in contrast to Cummings et al. (25), they made no distinction among those who walked more than 60 minutes per day. The number of hours spent on one’s feet may not be associated with fall-related fractures, and orher explanations may account for our findings. Respondent< inay have been unable to estimate or recall accurately the number of hours per day they spend on their feet; this variable may not be a reasonable proxy measure for time spenr walking; or the time reported may reflect a mixture of activities that have dissimilar effects. Such activities could inclucle standing while washing dishes as well as walking slowly or briskly. Additional research that focuses on specific activities is necessary to clarify the association of mild ro moderate types of exercise and fractures.
CONCLUSION The presence of any limitation in ADL stgnificantly modified the effect of vigorous physical activity. Vigorous activity was associated with a significantly lower risk of a serious fall-related fracture among subjects with no limitations but a higher fracture risk among those who have any limitations in ADL. Although some studies have suggested that mild or moderate exercise such as walking may reduce fracture risk, we did not find evidence to support this contention. However, the impact of light to moderate activity is difficult to assess.Studies better designed to categorize and measure types of light and moderate activities are needed to evaluate the benefit of these activities. Further research in elderly populations is required to determine the effects of specific types of exercise, such as walking, on the risk of fall-related fractures. If moderate activities can be shown to be beneficial in reducing falls, it would have important implications for future prevention efforts. Finally, our results suggest that for healthy elderly persons, an exercise program could effectively decrease the risk of fall-related fractures. For persons who have any limita-
Stevenset al.
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PHYSICAL
ACTIVITY
AND
FALL-RELATED
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FRACTURES
tions in ADL, more individualized programs may be needed to minimize the risk of fall injuries.
17. Gehlsen strength,
GM, Whaley and flexibility.
MH. Falls in the elderly: Part II. Balance, Arch Phys Med Rehabil. 1990;71:739-741.
We would like to thank the following members of the Study to Assess Falls among the Elderly (SAFE): Principal investigator, Richard W. Sattin, MD; administrative director, Albert0 Ros, MS; project directors, Carolee A. DeVito, PhD, MPH, and Phyllis A. Wingo, PhD, MS; project coordinators, Deborah A. Lambert, RN, MS, Edmond F. Maes, PhD, Juan G. Rodriguez, MD, MPH, and Judy A. Stevens, MS, MPH; Field coordinators, Sandra Bacchelli, MD, MPH, Ramon E. Barea, MSS, Michael A. Green, Donna L. Ragland, Michael Rybolowik, and Lance Simpson; administrative coordinators, Albert N. Brasile, MA, Harvey F. Davis, MPH, and Arthur V. Schletty; project associates, Christine M. Branche-Dorsey, PhD, MSPH, Sharon T. Clanton, Owen J. Devine, MS, Gitta A. Kastner, ART, Jean A. Langlois, Sc.D., James M. Mendlein, PhD, David E. Nelson, MD, MPH, Philip H. Rhodes, MS, Suzanne M. Smith, MD, MPH, Pamela M. Stack, Richard J. Waxweiler, PhD, and David F. Williamson, PhD
19. Lord SR, Caplan GA, Ward JA. Balance, reaction time, and muscle strength in exercising and nonexercising older women: A pilot study. Arch Phys Med Rehabil. 1993;74(8):837839.
18. Lord SR, Sambrook PN, Gilbert C, et al. Postural stability, fractures in the elderly: Results from the Dubbo Osteoporosis ology Study. Med J Austr. 1994;160(11):684-691.
MC, et al. The effects of exercise 20. Province MA, Hadley EC, Hombrook on falls in elderly patients-A preplanned metaanalysis of the FICSIT trials. JAMA. 1995;273(17):1341-1347. 21. Paganini-Hill A, Chao A, Ross RK, Henderson BE. Exercise and other factors in the prevention of hip fracture: The Leisure World study. Epidemiol. 1991;2:16-25. 22. Wickham CA, Walsh K, Cooper C, et al. Dietary activity, and risk of hip fracture: A prospective 1989;299(6704):889-892.
1. Brummel-Smith 16(2):377-393.
K.
Falls
2. Kanis JA, 1992;13(suppl
Pitt FA. l):S7-15.
in
the
aged.
Epidemiology
3. Lau EM, Donnan SP. Falls and hip fracture Pub Health. 1990;104(2):117-121.
Primary
of
Care.
osteoporosis.
1989; Bone.
in Hong Kong Chinese.
4. Mayo
NE, Komer-Bite&y N, Levy AR. Risk factors for fractures due to falls. Arch Phys Med Rehabil. 1993;74(9):917-921.
5. Boonen S, Dequeker J, Pelemans W. Risk factors for falls as a cause of hip fracture in the elderly. Acta Clin Belg. 1993;48(3):190-194. 6. Tinetti, ME, Speechley elderly persons living 1988;319(26):1701-1707.
M, Ginter in the
SF. Risk factors community. N
7. Sattin RW. Falls among older persons: A public Ann Rev Public Health. 1992;13:489-508.
for falls among Engl J Med.
health
perspective.
8. Aloia JF, Cohn SH, Ostuni JA, Cane R, Ellis K. Prevention of involutional bone loss by exercise. Ann Intern med. 1978;89:356-358. 9. Smith EL, Reddan W, Smith PE. Physical activity ities for bone mineral increase in aged women. erc. 1981;13:60-64.
and calcium modalMed Sci Sports Ex-
10. Krolner B, Toft B, Nielsen SP, Tondevold E. Physical exercise as prophylaxis against involutional vertebral bone loss: A controlled trial. Clin Sci. 1983;64(5):541-546. 11. Chow R, Harrison JE, Notarius C. Effect of two randomized exercise programmes on bone mass of healthy postmenopausal women. Br Med J. 1987;295:1441-1444. 12. Dalsky GP, Stocke KS, Ehsani AA, et al. Weight-bearing training and lumbar bone mineral content in postmenopausal Ann Intern Med. 1988;108:824-828.
exercise women.
13 Michel BA, Lane NE, Bloch DA, Jones HH, Fries JF. Effect of changes in weight-bearing exercise on lumbar bone mass after age fifty. Ann Med. 1991;23(4):397-401. 14. Prince RL, Smith M, Dick IM, et al. Prevention of postmenopausal osteoporosis: A comparative study of exercise, calcium supplementation, therapy. N Engl J Med. and hormone-replacement 1991;325:1189-1195. 15. Jaglal SB, Dreiger N, Darlington G. Past and recent physical and risk of hip fracture. Am J Epidemiol. 1993;138:107-118.
activity
16. Judge JO, Lindsey C, Underwood M, Winsemius D. Balance improvements in older women: Effects of exercise training. Phys Ther. 1993;73(4):254-265.
calcium, physical study. Br Med J.
23. Lau E, Donnan S, Barker DJ, Cooper C. Physical activity and calcium intake in fracture of the proximal femur in Hong Kong. Br Med J. 1988;297:1441-1443. 24. Cooper C, Barker DJ, Wickham and calcium intake in fracture Med J. 1988;297:1443-1446.
REFERENCES
falls and Epidemi-
C. Physical activity, muscle strength, of the proximal femur in Britain. Br
25. Cummings SR, Nevitt MC, Browner WS, et al. Risk factors for hip fracture in white women. Study of Osteoporotic Fractures Research Group. New England J Med. 1995;332(12):767-773. 26. DeVito CA, Lambert DA, elderly: Community-based 1988;36:1029-1035.
Sattin RW, et al. Fall injuries among the surveillance. J Am Geriatr Sot.
27. Sattin RW, Lambert Huber DA, DeVito CA, et al. The incidence of fall injury events among the elderly in a defined population. Amer J Epidemiol. 1990;131(6):1028-1037. 28. The Commission on Professional and Hospital tional Classification of Diseases. 9th ed. Clinical Arbor, MI: The Commission; 1980.
Activities. IntemaModification. Ann
29. Griffin MR, Wayne AR, Fought RL, Melton LJ III. Black-white differences in fracture rates. Am J Emidemiol. 1992;136(11):1378-1385. 30. Ainsworth Phys Activ
B. Gender differences J. 1993;2( l):l-16.
in physical
activity.
Women
Sport
31. Katz S, Ford AB, Moskowitz RW, et al. Studies of illness in the aged. The Index of ADL: A standardized measure of biological and psychosocial function. JAMA. 1963;185:914-919. 32. Folstein MF, Folstein SE, McHugh PR. Mini-mental method for grading the cognitive state of patients Psychiatr Res. 1975;12:189-198.
state: A practical for the clinician. J
33. Kramer M, German PS, Anthony JC, et al. Patterns of mental disorders among the elderly residents of eastern Baltimore. J Am Geriatr Sot. 1985;33:236-245. 34. Schlesselman JJ. Case-Control New York: Oxford University
Studies; Design, Press; 1982.
Conduct,
Analysis.
35. Breslow NE, Day NE. Statistical Methods in Cancer Research. V. 1. The Analysis of Case-Control Studies. Lyon: International Agency for Research on Cancer; 1980. 36. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Nat1 Cancer Inst 1959;22:719-748. 37. Nelson HD, Nevitt MC, Scott JC, Stone KL, Cummings SR. Smoking, alcohol, and neuromuscular and physical function in older women. JAMA. 1994;272(23):1825-1831. 38. Cummings SR, Kelsey JL, Nevitt MC, et al. Epidemiology of osteoporosis and osteoporotic fractures. Epidemiol Rev. 1985;7:178-208. 39. K&y JL, Browner WS, Se&y DG, Nevitt MC, Cummings SR. Risk factors for fractures of the distal forearm and proximal humerus. Am J Epidemiol. 1992;135:477489.
40. Hetzog AR, Rogers WL. Age and response rates to interview sample surveys. ] Gerontol. 1988;43(6):S200-205. 41. Kreiger N, Gross A, Hunter G. Dietary factors and fracture in postmenopausal women: A case-control study. Intl J Epidemol. 1992; 21(5):953-958. 42. Dipietro L, Caspersen CJ, Ostfeld AM, et al. A survey for assessing phystcal actwty among older adults. Med Sci Sports Exert. 1991;628-642.
43. Voorrips LE, Ravelli ACJ, Donglemens PCA 1)eurenhcrg I’, Van Staveren WA. A physical activity questionnaire fbr the elderly. Med Sci Sports Exert 1991:23:974-979. 44. Haskell WL, Taylor HL, Wood I’D, et al. Srrenr~xt:. physical actiwty, treadmill exercise test performance and plasma high-densny Iipoprotein cholesterol. Circulation. 1980;62(suppl IV):Si-61 45. Jacob DR, Ainsworth BE, Hartman TJ, Leon AS. A s~multimeous evaluation of 1C commonly used physical acttvir\ qwstuxmatireS. Med Sci Sports Exert. 1993;25:81-91.
Physical Activity, Functional Limitations, and the Risk of FallcRelated Fractures in Community-Dwelling Elderly JUDY A. STEVENS, MS, MPH, KENNETH E. POWELL, MD, MPH, SUZANNE M. SMITH, MD, MPH, PHYLLIS A. WINGO, PHD, MS, AND RICHARD W. SATTIN, MD
This case-control study examines the association of vigorous and mild physical activity with fallrelated fractures in a community-dwelling population age 65 and older in South Florida. Vigorous physical activity was defined as exercising, doing heavy housecleaning, or other hard labor three or more times per week in the month prior to the index date; mild physical uctioritywas dejined as the number of hours per day subjects reported spending on their feet. A case was any subject who sustained a fall-reiated fracture (ED-9CM-800 through ED-9CM-829) over a 21 -month period (n = 471). Controls werea 10% randomsampleselectedfrom the Health Care Financing Administration Medicare files (n = 712). The presence of any limitation in activities of daily living (ADL) significantly modified the effect of vigorous physical activity. Physically active subjects with no limitations (ADL = 0) were lesslikely to sustain a fall-related fracture than were inactive subjects, with an adjusted oddsratio (aOR) of0.6, (0.5-0.8 95% CI), and active subjectswith any limitation (ADL 2 I) had an aOR of 3.2 (1.1-9.8 95% CI) . Limiting this analysis to 159 hip fracture cases producedsimilar results. Mild physical activity was not associated with fracture. Theseresultssuggest that vigorous physical activity is associatedwith a lower fracture risk amongelderly personswho huue no limitations in ADL and with a higher risk among those with any limitations. 0 1997 by Elsevier
Science, Inc. KEY WORDS:
Ann Epidemiol 1997;7:54-61. Elderly, falls, fractures, physical activity, exercise, activities of daily living.
INTRODUCTION
Fractures due to falls are a significant problem among the elderly (1). The most frequent fractures involve the femoral neck, humerus, vertebra, radius, ulna, and bones of the pelvis, hand, and ankle (2), and most result from falls (3-5). In the United States, the morbidity and mortality associated with fractures can be expected to increase as the population ages.
Three components contribute to the risk of fractures: lack of bone strength, the risk of falling, and ineffective protective neuromuscular reactions when a fall occurs (4, 6, 7). Physical activity may reduce the risk of fractures by modifying all three components: preventing or reducing bone loss at all ages (g-15), increasing muscular strength,
From the National Center for Injury Prevention and Control (J.A.S., K.E.P., R.W.S.) and the Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA (S.M.S.); and the American Cancer Society, Atlanta, GA (P.A.W.). Address reprint requests to Judy A. Stevens, CDC/NCIPC, 4770 Buford Highway, Mailstop K63, Chamblee, GA 30341. Received November 10, 1995; revised July 3, 1996; accepted July 26, 1996. 0 1997 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
and improving balance (16-18), flexibility, coordination, and reaction time (19, 20). Although a number of recent studies have demonstrated a reduction in the risk of hip fracture with increasing activity, these studies used disparate definitions of physical activity, such as lists of various activities (15,21,22) and frequencies of walking and standing (23-25). The studies also included subjects in differing age ranges (15, 24) and failed to adjust adequately for potential confounders such as age (23), alcohol, and estrogen replacement therapy (ERT) (22). The purpose of this study was to address the following questions, adjusting for potential confounders. First, is current vigorous physical activity associated with a lower risk of fall-related fractures in men and women aged 65 and older? Second, is mild physical activity also associated with a lower risk of fall-related fractures in men and women aged 65 and older?
METHODS
The data for the current analysis were derived from the Study to Assess Falls among the Elderly (SAFE), which is described in detail elsewhere (26, 27). Briefly, this was a population-based, case-control study of fall-related injuries 1047s2797/97/$17.00 PII S1047-2797(96)00110-X
:;it i’,‘llbt‘i ai PHYSICAL ACTIVITY
among community-dwelling people aged 65 and older in a geographically defined area of Miami Beach, Florida. Potential caseswere ascertained through an active, population-based surveillance system that obtained data from South Miami Beach Fire Rescue summary reports, Dade County medical examiner investigation reports, and six study area hospital emergency department and inpatient medical records. These hospitals provided treatment for all serious injury casesthat occurred within the study area (27). Demographic and medical information were abstracted from medical records for inclusion in the surveillance system. A nosologist coded the anatomic nature of the injury (N-code) and the external cause of the fall injury (E-code) according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) (28), and the data were entered into a microcomputer data file. Because 87% of fall-related fractures occur in and around the home (29), caseswere defined as any study area resident aged 65 or older who received treatment for a newly diagnosed fracture (ICD-9CM-800 through ICD-9CM-829) due to an unintentional fall in or about their home (E849.0) that occurred between November 20, 1986, through August 31, 1988. Control subjects were randomly selected and comprised 10% of the population-based Health Care Financing Administration Medicare files of all persons aged 65 or older who resided in the study area in the period during which the caseswere diagnosed. Controls were frequency matched to the expected age distribution of casesbased on the results from a pilot study.
Data Collection Trained interviewers administered the questionnaire in English or Spanish (Cuban dialect), usually in the respondent’s home. Most information was self-reported and included data on personal and demographic characteristics including birth date, height, weight, physical activity (currently and at age 30), activities of daily living (ADL), postmenopausal estrogen use, and mental status. Recall was facilitated by using a calendar to identify periods and dates, and demonstration cards were used for questions about race, religion, marital status, and frequencies of occurrence. The index date for cases was the injury date. To make the titne from selection to interview approximately the same for cases and controls, the index date for controls was 1 month prior to their selection date. The reference period was the month before the index date. Because interviews were conducted in respondents’ homes and some fractures can require extended hospitalization, the interview deadline was 6 months after the index date.
55
AND FALL-REL/ITET, Fii,\IT1-!JREC
Definitions of Vigorous Physical Activity, Activity, and ADL
Mild Physical
Respondents who engaged in vigorous physical activity were those who answered “yes” to the question, “[Before the reference period] did you do exercise, heavy housecleaning, or other hard labor three or more times per week?” We included “heavy housecleaning” because women comprised approximately 60% of the over-65 population in the study area. Studies have shown that women spend more time and expend a greater amount of energy in household activities than do men (30). We chose the phrase “4lther hard labor” so that respondents would include additional activities that were not specifically mentioned in the question. The definition of mild physical activity was based on the only available relevant question, “Before [the reference period], about how many hours per day did you spend on your teet?” (categorized as none, up to 1, Z-4, 5-7, and 8 or more). Vigorous and mild physical activity were positively correlated (Spearman rank correlation = 0.32, P = 0.0001) alld showed good concordance; 61.3% of respondents who engaged in vigorous physical activity also reported spending 5 or more hours per day on their feet; 70.4% of those who did not engage in vigorous activity spent less than 5 hours :sday on their feet. Each subject’s level of dependence WASassessedusing a simplified version of the Katz index of XDL ( 7 1). Selfreported dependence (on a scale of 0 to 5 9 was defmed as requiring help in carrying out five basic dady activities: eating, bathing, dressing, transferring, ArId toileting. An ADL score of 0 meant that the respondent was independent in all five activities; a score of 1 or higher meant that the respondent was dependent in the ccm~a~~~-~lingnumher of activities. Mental Competency Assessment The respondent’s mental competency was :issessedbased on answers to the 21-question mental statkfs section of the questionnaire. Because cognitive impairment has been associated with a higher risk of falling (6), we computed a mental status score based on a subset of 16 questions and derived from the Mini-Mental State Exam developed by Folstein et al. (32). The 16 questions corresponded to the original Folstein items for Orientation, Registration, and Recall and had been validated for persons vged 65 and older from the Baltimore Survey of the Epidemiologic Catchment Area study (33). This study categorized an individual with a mental status score of I2 or less as cognitively impaired. Surrogate Information A proxy respondent was interviewed if an eligible individual was physically incapable of completing the questionnaire or mentally incompetent based on an initial screening at the beginning of the interview. Although there were specified hierarchical rules for selecting surrogates, beginning with a
56
Stevens et al. PHYSICAL ACTIVITY
spouse, a relative, then a friend or neighbor, one possible surrogate was available. Statistical
AEI’ Vol. 7, No. 1 Januq 1997. 54-61
AND FALL-RELATED FRACTURES
usually only
Analysis
In the univariate analyses, we calculated the crude odds ratios (cOR) and 95% confidence intervals (CI) for the dichotomous exposure variables defined and evaluated mild physical activity as a categorical variable using a chi-square test for trend (34). We used the Breslow-Day test for homogeneity (35) to assess interaction and the Mantel-Haenszel procedure (36) to adjust for the effects of potential confounders. We used unconditional logistic regression to estimate adjusted odds ratios (aORs) and 95% CI, simultaneously adjusting for potential confounders. Age, sex, ADL, exercise at age 30, ERT (women), Quetelet index, current calcium intake, mental status score, and whether or not physical activity data were supplied by a surrogate were evaluated as potential confounders. Current smoking and alcohol use were not found to be associated with fracture risk in this population (37). The full logistic model consisted of current activity, age, sex, activity at age 30, estrogen use (women only), mental status score, Quetelet index, and whether or not physical activity data were supplied by a surrogate. To develop the final model, we eliminated one variable at a time, selecting the variable with the highest nonsignificant P value. A covariate was considered a confounder and was retained in the model if removing it altered the OR for physical activity by 10% or more. RESULTS We excluded 20 cases and 15 controls who reported that they used a wheelchair exclusively before their injury (or whose wheelchair use was unknown) and 6 cases and 4 controls who did not provide meaningful information about physical activity. After exclusions, the response rate was 471/717 (65.7%) for cases and 712/1060 (67.0%) for controls. Reasons for nonparticipation included refusal (7.9% vs. 19.6%), death (9.9O/, vs. 1.6%), an inability to be located (3.3% vs. 5.7%), having moved outside the study area (8.0% vs. 2.6%), and other reasons (5.2% vs. 3.4%) for cases and controls, respectively. The average time from index date to interview was 2.6 months for cases and 1.9 months for controls. Four hundred seventy-one cases reported 523 fractures; 49 cases sustained multiple fractures at the time of their fall (Table 1). The hip ( net k o f f emur) was the most common fracture site. Table 2 presents selected sociodemographic characteristics of cases and controls. The average ages of cases and controls. The average ages of cases and controls were not significantly different (P > 0.05) when stratified by sex. Approximately 16% of cases and 26% of controls were of
TABLE 1. Distribution of fall-related 471 case subjects age 65 and older
fractures
Fracture site
n
(%I)
160 78 71 64 40 25 24 19 10 9 8 7 3 3 2 523
30.7 14.9 13.6 12.1 7.7 4.8 4.6 3.7 1.9 1.7 1.5 1.3 0.6 0.6 0.4 100.0
Neck of femur Humerus Radius/ulna Ribs, sternum Spine Pelvis Bones of the hand Skull Other parts of femur Ankle Tibia/fibula Foot Clavicle Patella Scapula Total
sustained by
* Forty-six casessustainedtwo fractures; three casessustainedthree fractures.
Hispanic origin; 98% of both cases and controls were white. Physical fraility, defined as impaired strength, mobility, balance, and endurance, appeared to be more prevalent among cases than controls. Compared with controls, cases tended to have a lower body mass index (33% vs. 24% in the lowest quartile of Quetelet index distribution), not participate in vigorous activity (72% vs. 63%), have a functional limitation (ADL 3 1; 18% vs. 12%), have a low mental status score (21% vs. ll%), and have activity data reported by a surrogate (12% vs. 5%). Most cases and controls did not smoke or drink. Respondents with physical activity information supplied by a surrogate differed from those with self-reported data (data not shown). They tended to be older, live in a nursing home at the time of their interview, not have completed high school, not smoke or drink, and have a lower Quetelet index. Among the cases, those with surrogate data were more apt to be male, under 85, and married. Among the controls, those with surrogate data were more likely to be female, over 85, and widowed. Cases and controls reported a similar number of chronic diseases. Vigorous activity was associated with an overall 30% decreased risk of fracture (cOR = 0.7,0.5-0.8 95% CI). In contrast, reported time spent on feet was not associated with fracture risk (Mantel-Haenszel summary OR = 1.08, 0.86-1.4 95% CI), and there was no evidence of a trend of lower fracture risk with increasing time spent on feet (P = 0.30). The majority of the 457 cases and 708 controls with ADL scores reported no limitations. Only 39 cases (9%) and 40 controls (6%) reported needing help with a single activity (ADL = 1); only 47 cases (10%) and 40 controls (6%) had ADL scores of 2 to 5. Among those with ADL
AEP Vol. 7, IL’o. 1 lantuq 1997: 54-61
Stw?ns et dl. AND FALL-RELATED FRACTURES
PHYSICAL ACTIVITY
TABLE 2. Selected characteristics of fracture casesand controls”
TABLE 2. continued Cases
CZXS
n=471
CtES
%
n = 712
%
103 368
21.9 78.1
181 531
25.4 74.6
0.16
AS 65-74 75-84 2 Rj
75 231 165
15.9 49. I 35.1
306 331 235
20.5 46.5 33.0
0.14
Race Whttr Black Other Unknown
463 2 0 6
98.3 0.4 0.0 1.3
699 3 5 5
98.2 0.4 0.7 0.7
0.23
Ethnicity Htspanic Non-Hispanic Unknown
77 389 5
16.3 82.6 1.1
186 521 5
26.1 73.2 0.7
0.0004
Education <3 9-l I 12 2 I3 Unknuwn
152 71 163 46 39
32.3 15.1 34.6 9.8 8.3
291 87 223 65 46
40.9 12.2 31.2 9.1 6.5
0.07
379 132
72.0 2X.0
446 266
62.6 37.4
0.001
6 47 207 98 65 48
1.5 10.0 43.9 20.8 13.8 10.2
6 70 324 174 112 26
0.8 9.8 45.5 24.4 15.7 3.7
0.0004
373 84 14
79.2 17.8 3.0
624 84 4
87.6 11.8 0.6
o.OQoo4
101 G2 8
21.4 76.9 I.7
80 626 6
11.2 87.9 0.8
< 0.00001
47 87 296
10.0 18.5 62.9
48 187 408
6.7 26.3 57.3
0.012
64 5
9.0 0.7
P value
Sex
Male Female
Vigorous activity NC1 Yes Hours/day spent on feet NCW I? Unknown Mariral status Ncwr married Married W1d0wed Separated :)I divorced linkmxvu Smoktng status Ncvcr smoked FOITMX mokrr (:rirrcnt imoker Unknown
38 3 2Y7
63.9
119
27.1
43 12
7.3 17
57
0.46
I.,
(continued)
Alcohol use (drink&k) None
--____
chses
‘Xl
n=471
Y/o
n = 712
369 32 27 29 14
78.3 6.8 5.7 6.2 3.0
515 72 ih ii) it,
71.3 10.1 79 ;.o i.7
0.13
154 198 74 9.5
32.7 42.0 15.7 9.6
lb7 334 I62 49
1’3.5 46.9 z.T.7 t>.‘)
O.ooo2
417 54
88.5 11.5
675 37
94.8 5.2
0.0#07
-----
P value
scores equal to or greater than 1, a higher percentage of cases than controls reported needing help for each of the five activities. The largest proportion (26% of cases and 20% of controls) needed help bathing; 19% af cases and 15% of controls needed help getting in or out of a bed or chair; 16% of cases and 12% of controls needed help dressing; 12% of cases and 7% of controls needed help going to the bathroom or using the toilet; less than 4% of either cases or controls reported needing help eating. Because of the small proportion of cases and controls with ADL scores greater than 1, it was necessary to dichotomize this variable. After stratifying by ADL score (0, 3 1%; Table 3), we observed a significant interaction between the presence of any limitation and current vigorous activity (P = 0.001). There was no interaction between the presence of any limitation and mild physical activity (ADL = 0, cOR = 0.8; ADL 2 1, cOR = 1.2, P =: Q.48). Vigorous physical activity was associated with a lower risk among respondents with an ADL score of zero (cOR = 0.6), but with a higher risk among those with an ADL score equal to or greater than 1 (cOR = 2.6). The stratum-specific ORs were not significantly different depending on whether the data were supplied by the respondent or 3 surrogate. Using unconditional logistic regression to adjust simultaneously for confounding (Table 4), the aOR for respondents with an ADL score of zero was 0.6 (0.4-J.8 95% CI); the aOR for respondents with an ADL score equal to or greater than 1 was 3.2 (1.1-9.8 95% CI). When this analysis was restricted to women and adjusted for ERT (ever/never), the point estimate for women with no limitations became 0.5 ([email protected],95% CI), and the aOR for women with any limitation increased to 5.7 (1. S-25.0 95% CI). Lirnitmg the analv-
Stevens et al. PHYSICAL ACTIVITY
58
TABLE
AEP Vol. 7, No. 1 January 1997: 54-61
AND FALL-RELATED FRACTURES
3. Crude odds ratios (cOR)
and 95% CI between
vigorous
physical
activity,
mild activity, ADL 2 1
ADL = 0
Vigorous activity YES No Mild activity Yes NO
and risk of fracture,
stratified
Cases
Controls
cOR
95% CI
CSSS
Controls
cOR
95% Cl
P-value for heterogeneity
110 263
256 368
0.6
(0.4-0.8)
18 66
8 76
2.6
(1.1-6.2)
0.001”
144 193
271 332
0.9
(0.7-1.2)
15 62
13 67
1.2
(0.5-2.8)
0.48b NS
u& = 10.1. bx:# = 0.5.
sis to 33 men and 126 women who sustained a hip fracture resulted in very similar aORs. Among people with an ADL score of zero, the aOR for hip fracture was 0.6 (0.4-0.9 95% CI); among people with a higher ADL score, the aOR was 4.1 (1.3-12.9 95% CI).
DISCUSSION Overall, vigorous physical activity in this noninstitutionalized elderly population was associated with a lower risk of a fall in the home resulting in a serious fracture, a finding consistent with results from previous studies (17, 20, 38). However, among the subgroup of elderly persons with any limitations in ADL, vigorous activity was associated with a higher risk of serious fracture. No prior studies have reported a differential effect on vigorous activity on the risk of fracture among subgroups of the elderly, a finding that has important implications because exercise increasingly is recommended as a way to improve the quality of life and general health of older persons. Although we observed no risk differences between
4. Adjusted odds ratios (aOR)” for the association between vigorous physical activity and risk of fracture, stratified bv (ADL score TABLE
ADL 5 0
ADL = 0
Vigorous activity Female Age 75-84 285 Low mental status score Quetelet index, Lowest 25% Highest 25%
aOR
95% CI
aOR
95% Cl
0.6 1.3
(0.4-0.8) (0.9-1.8)
3.2 0.6
(1.1-9.8) (0.2-1.5)
1.2 1.3
(0.9-1.6) (0.8-2.1)
0.5 0.3
(0.2-1.2) (0.1-1.0)
2.0
(1.3-3.3)
1.5
(0.7-3.3)
1.4 0.9
(1.0-1.9) (0.6-1.3)
1.5 0.3
(0.7-3.5) (0.1-0.8)
‘Odds ratio adjustedfor sex (M/F), age (65-74, 75-84, 3 85), mental status SCOW (S 12, > 12), and Quetelet index (lowest 25%, middle 50%, highest 25%).
those with an ADL score of 1 and those with an ADL score greater than 1, we had relatively few respondents in the latter category. Moreover, ADL score is a crude measure for a wide range of functional limitations. Research is needed to refine the relationships among physical activity, ADL, and falls. This is the first population-based case-control study of fractures due to falls in a geographically defined, noninstitutionalized elderly population. Cases were ascertained through an active population-based surveillance system that used four sources (Fire Rescue, emergency departments, inpatient hospital records, and Dade County medical examiner reports) to identify serious fractures that occurred in the study area. Outcomes were documented using medical records. We consider case ascertainment to be virtually complete for serious fractures. The distribution of serious fractures in this study was similar to that in a comparable population of Tennessee Medicaid enrollees aged 65 and older (which included fractures treated in hospitals and doctor’s offices) (29). However, we observed smaller percentages for fractures of the skull, ankle, tibia/fibula, and foot. Because we could not ascertain the number of fractures that may have been treated in a physician’s office, our findings may not apply to less serious fractures. Although the epidemiology for various fractures differs (38, 39), vigorous physical activity appears to reduce the risk of many fall-related fractures. When this analysis was repeated using 159 hip fracture cases (126 women and 33 men), the ORs were very similar to those seen for all fractures combined. Some of the limitations of this study should be noted. First, the study population in South Miami Beach may not be representative of other community-dwelling elderly populations, which could limit the generalizability of these findings. Second, although the study achieved an overall participation rate of about 67%, comparable to that in similar studies (15, 24, 40, 41), the possibility of selection bias exists for both cases and controls. However, we think that it is un-
PHYSICAL ACTIVITY
likely to account for our findings because the more likely biases would have shifted the point estimate toward the null value. Cases were more likely to have died than controls and to have data reported by a surrogate. This suggests that interviewed caseswere healthier and more likely to be physically active than noninterviewed cases. If the participating caseswere at lower risk for a fall-related fracture than nonparticipants, the point estimate would be biased toward the null value, leading to an underestimate of risk. In addition, controls were harder to locate and more likely to refuse being interviewed than cases. No additional information was available about nonparticipant controls. These controls may have been busier and engaged in more activities outside their homes than participating controls, suggesting that they may have been healthier. If interviewed controls were less healthy and less active than nonparticipants, the ORs would be biased toward the null value and would be conservative estimates. Third, participants with ADL scores of 1 or above may have responded differently from participants without functional limitations to the question about “exercise, heavy housecleaning, or other hard labor.” Some may have considered everyday activities to be vigorous. If so, the true association between vigorous activity and fall-related fractures would be slightly lower than our estimate. A fourth limitation is the classification of physical activity levels among this group of elderly cases and controls. We classified subjects’ participation in vigorous and mild activity based on their response to a single question for each. Cases and controls were considered to be vigorously active if they indicated that in the month before the index date they had done “exercise, heavy housecleaning, or other hard labor three or more times per week.” We used the term hard labor so that respondents would include activities that they might not consider to be exercise. We attempted to minimize recall bias by asking about recent physical activity. Few questionnaires that assessphysical activity have been evaluated among the elderly. However, at least two have shown reasonable reliability and validity among adults 63 to 80 and 60 to 86 years of age, especially for more vigorous activities (42,43). In addition, among adults 60 to 69 years of age in the Lipid Research Clinics Prevalence Study, selfreported responses to two questions about vigorous activity, similar to the one question in the SAFE questionnaire, correlated with physiologic measures of fitness (44). Therefore, although firmer evidence of validity would be desirable, reported information about participation in vigorous physical activity appears to be reasonably accurate for both elderly subjects and younger adults (45). Of greater concern is our measurement of “mild)’ activity. Our study is consistent with others, which generally have found that vigorous activity is associated with a lower risk of hip fractures due to falls (15, 21, 22, 24). It is less clear whether light to moderate activity in the elderly also de-
:;tt,b,erlset d. AND FALL-RELATER Fli \(7-UREc
59
creasesrisk. Based on a single question, we did not find that the number of hours spent on one’s feet was associated with the risk of fracture, regardless of ADL score. Our results differ somewhat from three previous hip fracture studies that specifically examined the influence of standing (25), walking (3), and standing, walking speed, and walking time (24). In a large prospective study, Cummings et al. (25) observed that women who spent less than 4 hours a day on their feet had a 70% higher risk of fracture than women who spent more time on their feet. Among women in Hong Kong, Lau et al. (3) reported a significantly increased risk associated with walking less often than once a day either uphill or carrying a load. Cooper et al. (24) reported that fracture risk increased with shorter standing times and slower walking speeds. They did not observe an association between reduced walking time and increased risk. but, in contrast to Cummings et al. (25), they made no distinction among those who walked more than 60 minutes per day. The number of hours spent on one’s feet may not be associated with fall-related fractures, and orher explanations may account for our findings. Respondent< inay have been unable to estimate or recall accurately the number of hours per day they spend on their feet; this variable may not be a reasonable proxy measure for time spenr walking; or the time reported may reflect a mixture of activities that have dissimilar effects. Such activities could inclucle standing while washing dishes as well as walking slowly or briskly. Additional research that focuses on specific activities is necessary to clarify the association of mild ro moderate types of exercise and fractures.
CONCLUSION The presence of any limitation in ADL stgnificantly modified the effect of vigorous physical activity. Vigorous activity was associated with a significantly lower risk of a serious fall-related fracture among subjects with no limitations but a higher fracture risk among those who have any limitations in ADL. Although some studies have suggested that mild or moderate exercise such as walking may reduce fracture risk, we did not find evidence to support this contention. However, the impact of light to moderate activity is difficult to assess.Studies better designed to categorize and measure types of light and moderate activities are needed to evaluate the benefit of these activities. Further research in elderly populations is required to determine the effects of specific types of exercise, such as walking, on the risk of fall-related fractures. If moderate activities can be shown to be beneficial in reducing falls, it would have important implications for future prevention efforts. Finally, our results suggest that for healthy elderly persons, an exercise program could effectively decrease the risk of fall-related fractures. For persons who have any limita-
Stevenset al.
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PHYSICAL
ACTIVITY
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FALL-RELATED
AEP Vol. 7, No. I Janury 1997: 54-61
FRACTURES
tions in ADL, more individualized programs may be needed to minimize the risk of fall injuries.
17. Gehlsen strength,
GM, Whaley and flexibility.
MH. Falls in the elderly: Part II. Balance, Arch Phys Med Rehabil. 1990;71:739-741.
We would like to thank the following members of the Study to Assess Falls among the Elderly (SAFE): Principal investigator, Richard W. Sattin, MD; administrative director, Albert0 Ros, MS; project directors, Carolee A. DeVito, PhD, MPH, and Phyllis A. Wingo, PhD, MS; project coordinators, Deborah A. Lambert, RN, MS, Edmond F. Maes, PhD, Juan G. Rodriguez, MD, MPH, and Judy A. Stevens, MS, MPH; Field coordinators, Sandra Bacchelli, MD, MPH, Ramon E. Barea, MSS, Michael A. Green, Donna L. Ragland, Michael Rybolowik, and Lance Simpson; administrative coordinators, Albert N. Brasile, MA, Harvey F. Davis, MPH, and Arthur V. Schletty; project associates, Christine M. Branche-Dorsey, PhD, MSPH, Sharon T. Clanton, Owen J. Devine, MS, Gitta A. Kastner, ART, Jean A. Langlois, Sc.D., James M. Mendlein, PhD, David E. Nelson, MD, MPH, Philip H. Rhodes, MS, Suzanne M. Smith, MD, MPH, Pamela M. Stack, Richard J. Waxweiler, PhD, and David F. Williamson, PhD
19. Lord SR, Caplan GA, Ward JA. Balance, reaction time, and muscle strength in exercising and nonexercising older women: A pilot study. Arch Phys Med Rehabil. 1993;74(8):837839.
18. Lord SR, Sambrook PN, Gilbert C, et al. Postural stability, fractures in the elderly: Results from the Dubbo Osteoporosis ology Study. Med J Austr. 1994;160(11):684-691.
MC, et al. The effects of exercise 20. Province MA, Hadley EC, Hombrook on falls in elderly patients-A preplanned metaanalysis of the FICSIT trials. JAMA. 1995;273(17):1341-1347. 21. Paganini-Hill A, Chao A, Ross RK, Henderson BE. Exercise and other factors in the prevention of hip fracture: The Leisure World study. Epidemiol. 1991;2:16-25. 22. Wickham CA, Walsh K, Cooper C, et al. Dietary activity, and risk of hip fracture: A prospective 1989;299(6704):889-892.
1. Brummel-Smith 16(2):377-393.
K.
Falls
2. Kanis JA, 1992;13(suppl
Pitt FA. l):S7-15.
in
the
aged.
Epidemiology
3. Lau EM, Donnan SP. Falls and hip fracture Pub Health. 1990;104(2):117-121.
Primary
of
Care.
osteoporosis.
1989; Bone.
in Hong Kong Chinese.
4. Mayo
NE, Komer-Bite&y N, Levy AR. Risk factors for fractures due to falls. Arch Phys Med Rehabil. 1993;74(9):917-921.
5. Boonen S, Dequeker J, Pelemans W. Risk factors for falls as a cause of hip fracture in the elderly. Acta Clin Belg. 1993;48(3):190-194. 6. Tinetti, ME, Speechley elderly persons living 1988;319(26):1701-1707.
M, Ginter in the
SF. Risk factors community. N
7. Sattin RW. Falls among older persons: A public Ann Rev Public Health. 1992;13:489-508.
for falls among Engl J Med.
health
perspective.
8. Aloia JF, Cohn SH, Ostuni JA, Cane R, Ellis K. Prevention of involutional bone loss by exercise. Ann Intern med. 1978;89:356-358. 9. Smith EL, Reddan W, Smith PE. Physical activity ities for bone mineral increase in aged women. erc. 1981;13:60-64.
and calcium modalMed Sci Sports Ex-
10. Krolner B, Toft B, Nielsen SP, Tondevold E. Physical exercise as prophylaxis against involutional vertebral bone loss: A controlled trial. Clin Sci. 1983;64(5):541-546. 11. Chow R, Harrison JE, Notarius C. Effect of two randomized exercise programmes on bone mass of healthy postmenopausal women. Br Med J. 1987;295:1441-1444. 12. Dalsky GP, Stocke KS, Ehsani AA, et al. Weight-bearing training and lumbar bone mineral content in postmenopausal Ann Intern Med. 1988;108:824-828.
exercise women.
13 Michel BA, Lane NE, Bloch DA, Jones HH, Fries JF. Effect of changes in weight-bearing exercise on lumbar bone mass after age fifty. Ann Med. 1991;23(4):397-401. 14. Prince RL, Smith M, Dick IM, et al. Prevention of postmenopausal osteoporosis: A comparative study of exercise, calcium supplementation, therapy. N Engl J Med. and hormone-replacement 1991;325:1189-1195. 15. Jaglal SB, Dreiger N, Darlington G. Past and recent physical and risk of hip fracture. Am J Epidemiol. 1993;138:107-118.
activity
16. Judge JO, Lindsey C, Underwood M, Winsemius D. Balance improvements in older women: Effects of exercise training. Phys Ther. 1993;73(4):254-265.
calcium, physical study. Br Med J.
23. Lau E, Donnan S, Barker DJ, Cooper C. Physical activity and calcium intake in fracture of the proximal femur in Hong Kong. Br Med J. 1988;297:1441-1443. 24. Cooper C, Barker DJ, Wickham and calcium intake in fracture Med J. 1988;297:1443-1446.
REFERENCES
falls and Epidemi-
C. Physical activity, muscle strength, of the proximal femur in Britain. Br
25. Cummings SR, Nevitt MC, Browner WS, et al. Risk factors for hip fracture in white women. Study of Osteoporotic Fractures Research Group. New England J Med. 1995;332(12):767-773. 26. DeVito CA, Lambert DA, elderly: Community-based 1988;36:1029-1035.
Sattin RW, et al. Fall injuries among the surveillance. J Am Geriatr Sot.
27. Sattin RW, Lambert Huber DA, DeVito CA, et al. The incidence of fall injury events among the elderly in a defined population. Amer J Epidemiol. 1990;131(6):1028-1037. 28. The Commission on Professional and Hospital tional Classification of Diseases. 9th ed. Clinical Arbor, MI: The Commission; 1980.
Activities. IntemaModification. Ann
29. Griffin MR, Wayne AR, Fought RL, Melton LJ III. Black-white differences in fracture rates. Am J Emidemiol. 1992;136(11):1378-1385. 30. Ainsworth Phys Activ
B. Gender differences J. 1993;2( l):l-16.
in physical
activity.
Women
Sport
31. Katz S, Ford AB, Moskowitz RW, et al. Studies of illness in the aged. The Index of ADL: A standardized measure of biological and psychosocial function. JAMA. 1963;185:914-919. 32. Folstein MF, Folstein SE, McHugh PR. Mini-mental method for grading the cognitive state of patients Psychiatr Res. 1975;12:189-198.
state: A practical for the clinician. J
33. Kramer M, German PS, Anthony JC, et al. Patterns of mental disorders among the elderly residents of eastern Baltimore. J Am Geriatr Sot. 1985;33:236-245. 34. Schlesselman JJ. Case-Control New York: Oxford University
Studies; Design, Press; 1982.
Conduct,
Analysis.
35. Breslow NE, Day NE. Statistical Methods in Cancer Research. V. 1. The Analysis of Case-Control Studies. Lyon: International Agency for Research on Cancer; 1980. 36. Mantel N, Haenszel W. Statistical aspects of the analysis of data from retrospective studies of disease. J Nat1 Cancer Inst 1959;22:719-748. 37. Nelson HD, Nevitt MC, Scott JC, Stone KL, Cummings SR. Smoking, alcohol, and neuromuscular and physical function in older women. JAMA. 1994;272(23):1825-1831. 38. Cummings SR, Kelsey JL, Nevitt MC, et al. Epidemiology of osteoporosis and osteoporotic fractures. Epidemiol Rev. 1985;7:178-208. 39. K&y JL, Browner WS, Se&y DG, Nevitt MC, Cummings SR. Risk factors for fractures of the distal forearm and proximal humerus. Am J Epidemiol. 1992;135:477489.
40. Hetzog AR, Rogers WL. Age and response rates to interview sample surveys. ] Gerontol. 1988;43(6):S200-205. 41. Kreiger N, Gross A, Hunter G. Dietary factors and fracture in postmenopausal women: A case-control study. Intl J Epidemol. 1992; 21(5):953-958. 42. Dipietro L, Caspersen CJ, Ostfeld AM, et al. A survey for assessing phystcal actwty among older adults. Med Sci Sports Exert. 1991;628-642.
43. Voorrips LE, Ravelli ACJ, Donglemens PCA 1)eurenhcrg I’, Van Staveren WA. A physical activity questionnaire fbr the elderly. Med Sci Sports Exert 1991:23:974-979. 44. Haskell WL, Taylor HL, Wood I’D, et al. Srrenr~xt:. physical actiwty, treadmill exercise test performance and plasma high-densny Iipoprotein cholesterol. Circulation. 1980;62(suppl IV):Si-61 45. Jacob DR, Ainsworth BE, Hartman TJ, Leon AS. A s~multimeous evaluation of 1C commonly used physical acttvir\ qwstuxmatireS. Med Sci Sports Exert. 1993;25:81-91.