The relationship among physical activity, obesity, and physical function in community-dwelling older women

Preventive Medicine 39 (2004) 74 – 80 www.elsevier.com/locate/ypmed

The relationship among physical activity, obesity, and physical function in community-dwelling older women Jennifer S. Brach, Ph.D., P.T., G.C.S., a,* Jessie M. VanSwearingen, Ph.D., P.T., a Shannon J. FitzGerald, Ph.D., b,c Kristi L. Storti, M.S., d and Andrea M. Kriska, Ph.D. d a

Department of Physical Therapy, School of Health and Rehabilitation Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA b Cooper Institute, Dallas, TX 75230, USA c Department of Kinesiology, Health Promotion and Recreation, College of Education, University of North Texas, Denton, TX 76203, USA d Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15260, USA Available online 9 April 2004

Abstract Background. The relationship between obesity and physical function is not well understood. Physical activity may be a key factor impacting on the relationship between obesity and physical function. Methods. Subjects included 171 community-dwelling women (mean age = 74.3, SD = 4.3) participating in a 14-year follow-up study to a walking intervention trial. Measures of obesity [body mass index (BMI)] and physical activity (Modified Paffenbarger Questionnaire) were collected in 1982, 1985, 1995, and 1999. Physical function was assessed in 1999 using the Functional Status Questionnaire (FSQ) and gait speed. Results. Measures of obesity from 1982 to 1995 and measures of physical activity from 1982 to 1995 were related to physical function in 1999. However, hierarchical regression analysis to predict physical function in 1999 controlling for the presence of chronic conditions indicated that physical activity from 1982 to 1995, and not obesity from 1982 to1995, was an independent predictor of physical function (FSQ: adjusted R2 = 0.09, F = 4.68, P < 0.001; gait speed: adjusted R2 = 18.0, F = 9.41, P < 0.0001. Conclusion. Physical activity appears to be as important if not more important than body weight in predicting future physical function. D 2004 The Institute For Cancer Prevention and Elsevier Inc. All rights reserved. Keywords: Obesity; Physical activity; Physical function

Introduction Obesity is a major problem in the United States and contributes to many negative health conditions. In a recent report, approximately 30% of adults in the United States are obese, defined as having a body mass index of greater than 30 kg/m2. Rates of obesity increase with age, with older adults (i.e., age 60– 74) having the highest rates of obesity [1]. Given that overweight and obesity are strongly related to morbidity and mortality [2– 5], it is a major public health concern in the older adult population.

* Corresponding author. Department of Physical Therapy, School of Health and Rehabilitation Sciences, University of Pittsburgh, 6035 Forbes Tower, Pittsburgh, PA 15260. Fax: +1-412-383-6629. E-mail address: [email protected] (J.S. Brach).

Younger and older adults with greater levels of obesity have poorer physical function [6 – 10], and greater amounts of obesity are predictive of declines in physical function [7,8]. Aging is related to a decline in physical function [11], with older adults who are overweight being at even greater risk for a decline in physical function. A concerted effort to target interventions to this high-risk population of overweight, older persons is needed. In contrast, being physically active is associated with less decline of physical function in older adults [12 – 22]. However, whether physical activity can prevent the decline of physical function in overweight older persons is not known. The purpose of this study is to examine the cross-sectional and longitudinal associations among obesity, physical activity, and physical function over a 17-year time period in community-dwelling older women.

0091-7435/$ - see front matter D 2004 The Institute For Cancer Prevention and Elsevier Inc. All rights reserved. doi:10.1016/j.ypmed.2004.02.044

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Methods A randomized controlled trial to examine the effects of walking on measures of bone in postmenopausal women was conducted from 1982 to 1985 in Pittsburgh, PA [23 – 25]. Women who volunteered and who met the following four baseline criteria were eligible for the randomized controlled trial: (1) aged 50– 65 years, (2) at least 1 year after cessation of menses, (3) abstention from estrogen replacement therapy, and (4) no physical limitations that might preclude walking. Two hundred twenty-nine white, postmenopausal women were randomly assigned to either a walking intervention or a control group. At the end of the trial, women in the walking group had significantly higher levels of physical activity assessed both subjectively and objectively [25]. In 1995, a follow-up telephone interview was administered to the cohort of women who participated in this clinical trial to determine the effects of the walking intervention on physical activity levels and health status a decade later [26]. In 1999, the surviving women from the original clinical trial were asked to return to the clinic for a comprehensive evaluation including measures of heart disease, bone density, body composition, physical activity levels, health status, and functional status. Of the original 229 women who participated in the randomized controlled trial, 171 women completed the clinic visit in 1999, 17 participated in phone interviews only (14 had complete phone interviews and 3 had incomplete phone interviews), 20 were deceased, 8 too sick to participate, 10 were lost to follow-up, and 3 refused to participate. Therefore, measures of obesity (BMI), physical activity, and physical function were available on 171 women. This research was approved by the University of Pittsburgh Institutional Review Board and informed consent was obtained from all participants before their participation in the study. Physical activity Physical activity levels were measured at four time points (1982, 1985, 1995, and 1999). Self-reported physical activity was measured using a modified version of the Paffenbarger Questionnaire at all of these time points [27]. In 1982 and 1985, the physical activity questionnaire included items that measured the number of blocks walked and the amount of physical activity from sport/leisure activities over the past week. In 1995 and 1999, the physical activity questionnaire included items that measured the amount of physical activity from walking for exercise and sport/leisure activities. In 1995 and 1999, total activity was calculated for the week averaged over the past year. The women were classified as being more or less active using physical activity levels determined by questionnaire. The women were classified based upon whether they reported participating in 1000 kcal/week of physical activity, which is representative of participating in 30 min of moderate physical

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activity on most days of the week (i.e., the Surgeon General’s recommended level of physical activity) [28,29]. In 1999, physical activity was also measured using a pedometer. The participants were asked to wear the pedometer for seven consecutive days and to record in a diary the number of steps taken on each day. The number of steps taken in the seven day period was averaged to achieve a single measure of physical activity (i.e. mean number of steps per day). Physical function In 1999, physical function was measured using both selfreport and performance-based measures. Self-report The Functional Status Questionnaire (FSQ) was used as the self-report measure of function [30]. The questions of the FSQ inquire about the amount of difficulty a person has completing a task during the past month. The two activities of daily living (ADL) sections of the FSQ, basic activities of daily living and instrumental activities of daily living, were selected for examination. The basic ADL section includes questions about difficulty with eating, dressing, bathing, and mobility tasks. The instrumental ADL section includes questions about difficulty walking several blocks, climbing stairs, doing housework, shopping, using public transportation, and doing vigorous activities. Scores on the basic ADL and instrumental ADL sections of the FSQ range from 0 to 100 with lower scores representing greater difficulty. Scores on the basic ADL and instrumental ADL sections were combined for a summary ADL score that could possibly range from 0 to 200, with higher scores representing better physical function. The ADL and instrumental ADL subscales of the FSQ have demonstrated internal consistency (a = 0.65– 0.82) in a sample of greater than 1000 ambulatory patients between the ages of 19 and 96 (60% of the sample was 60 years of age or older) [30]. In a sample of older adults, the FSQ has also been shown to exhibit construct and convergent validity by comparison to health status measures such as reported bed disability days and restricted activity days [31]. Performance-based Gait speed was used as a performance-based measure of physical function. Gait speed was measured using an instrumented walkway, the GaitMat IIk analysis system [32]. The GaitMat IIk is an automated gait analysis system based on the opening and closing of pressure sensitive switches when the participant walks on a 4-m-long walkway. In addition to the 4-m-long walkway, there are initial and final 1-m sections to allow for acceleration and deceleration of the participant. Gait speed was determined by dividing the distance traversed in meters by the time in seconds between the first and last switch closure. A gait speed of 1.2– 1.3 m/s is considered normal for adults [33,34].

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Obesity Body mass index (BMI) was used as the measure of obesity. Height and weight were measured at each of the clinic visits (1982, 1985, and 1999). In 1995, the participant self-reported their height and weight as part of the phone interview. Body mass index was calculated using the measures of height and weight (weight in kilograms/height in meters squared). Using BMI, the women were classified as being underweight (BMI < 18.5 kg/m2), normal weight (BMI between 18.5 and 24.9 kg/m2), overweight (BMI between 25.0 and 29.9 kg/m2), or obese (BMI z 30 kg/m2) [35].

Presence of chronic conditions A structured interview was used to assess the women’s health status. The women were asked if they were ever told by a physician that they had a list of medical conditions including such conditions as heart disease, liver disease, lung disease, arthritis, diabetes, and neurologic conditions. The number of chronic conditions reported was added to create an index of chronic conditions.

Data analysis One-way analysis of variance for normally distributed data and Kruskal –Wallis test for non-normally distributed data were calculated to test for differences in physical function and physical activity between the groups defined by BMI (normal weight, overweight, and obese). Two women were considered underweight (i.e., BMI V 18.5 kg/m2) and were excluded from these analyses since being underweight can be a result of poor health and can limit physical function [36]. Post hoc analysis (Scheffe test) was used to determine group differences [37]. To examine the role physical activity plays in the association between obesity and physical function, physical function was examined after stratifying the women by groups defined by both BMI and physical activity level. One-way ANOVA with post hoc analysis (Scheffe test) was used to compare physical function between the four groups: (1) normal weight, active; (2) normal weight, inactive; (3) overweight/obese, inactive; and (4) overweight/obese, active.

For the longitudinal analyses, the women were classified as always overweight, never overweight, or sometimes overweight using BMI measures from 1982, 1985, and 1995. Women who had a BMI z 25 kg/m2 in 1982, 1985, and 1995 were classified as always overweight. Women who had a BMI < 25 kg/m2 in 1982, 1985, and 1995 were classified as never overweight. Women who had a BMI z 25 kg/m2 in one or two of the following time periods 1982, 1985, or 1995 were classified as sometimes overweight. Similar classifications were constructed for physical activity: always active reported z1000 kcal/week in 1982, 1985, and 1995; always inactive reported <1000 kcal/week of activity in 1982, 1985, and 1995, sometimes active, reported z1000 kcal/week of activity in 1982, 1985, or 1995. To identify which factors (BMI, 1982 – 1995 and physical activity, 1982– 1995) best predicted physical function in 1999, hierarchical linear regression was used. A series of models were created to examine the contribution of body weight and physical activity to the prediction of physical function. Two series of models were examined, the first series of models had FSQ score, representing physical function, as the dependent variable, and the second series of models had gait speed, representing physical function, as the dependent variable. In both series of models, weight (always overweight, sometimes overweight, never overweight) was the independent variable in model one. In model two, physical activity (always active, sometimes active, or never active) was the independent variable. In model three, both weight and physical activity were entered into the model as independent variables. All models were adjusted for age and chronic conditions.

Results The mean age of the women was 74.3 (SD = 4.3) years. On average, the women reported minimal difficulty with ADL and IADL (mean FSQ = 189.5, SD = 17.4) and the women walked at a near normal gait speed (mean = 1.11 m/s, SD = 0.22) [33,34]. Sixty-one percent of the sample was considered overweight or obese as indicated by a BMI z 25 kg/m2. Cross-sectional analyses (1999) Physical activity and physical function differed among the BMI groups (Table 1). Women who were normal weight

Table 1 Cross-sectional analysis of obesity, physical activity, and physical function in 1999 Normal weighta mean (SD) Modified Paffenbarger Questionnaire (kcal/week) Pedometer (steps/day) Functional Status Questionnaire (0 – 200) Gait speed (m/s)

*

1641 (1207) n = 64 6754 (3547)* n = 63 195.4 (9.1)* n = 64 1.20 (0.18)* n = 64

Overweighta mean (SD)

Obesea mean (SD)

P value

1195 (1366) n = 63 4997 (2496) n = 60 185.5 (21.6) n = 62 1.08 (0.23) n = 62

1045 (1148) n = 42 4150 (2626) n = 40 187.6 (16.4) n = 41 1.05 (0.21) n = 41

0.04 <0.0001 0.002 0.0005

a Normal weight = BMI 18.5 – 24.9 kg/m2; overweight = BMI 25 – 29.9 kg/m2; obese = BMI z 30 kg/m2. * Indicates group that is different ( P < 0.05) from all others in post hoc analyses.

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Table 2 Mean (SD) physical function by physical activitya and weight groups: cross-sectional analysis, 1999 Normal weight BMI 18.5 – 24.9 kg/m2

Functional Status Questionnaire (0 – 200) Gait speed (m/s)

Overweight/obese BMI z 25 kg/m2

Inactive n = 25

Active n = 39

Inactive n = 59

Active n = 45

192.6 (11.8) 1.17 (0.15)

197.2 (6.3) 1.22 (0.19)

182.5 (21.9)** 1.02 (0.23)**

191.5 (14.6) 1.13 (0.19)

P value*

0.0001 <0.0001

a

Inactive = reported <1000 kcal/week of physical activity on the Modified Paffenbarger Questionnaire in 1999; Active = reported z1000 kcal/week of physical activity on the Modified Paffenbarger Questionnaire in 1999. * P value for ANOVA to test difference between groups. ** Indicates that the overweight/obese inactive group is different ( P < 0.05) from all others in post hoc analyses. Normal weight inactive, normal weight active, and overweight/obese active had similar scores on the Functional Status Questionnaire and similar gait speeds.

were more active based on the physical activity questionnaire and the pedometer and had better physical function as measured by the FSQ and gait speed than the overweight and obese women. Post hoc analyses revealed that the overweight and obese women had similar levels of physical activity and physical function, therefore, these groups were combined for all further analyses. Physical function was examined after stratifying the sample by weight and activity level. Women who were normal in weight were more likely to be active than women who were overweight/obese (61% and 43% were active, respectively). We found significant differences in

FSQ score and gait speed for the four groups of women, normal weight active, normal weight inactive, overweight/ obese inactive, and overweight/obese active (Table 2). Post hoc analyses using the Scheffe test revealed that the overweight/obese inactive group reported more ADL difficulty and walked slower than the normal weight active and normal weight inactive groups. The overweight/obese active group reported similar levels of ADL difficulty, as measured by the FSQ, and walked at a similar gait speed as the normal weight active and normal weight inactive groups. Adjusting for age did not significantly change the findings.

Fig. 1. Weight and physical activity in 1982, 1985, and 1995 and disability in 1999. Weight classifications: Always overweight, body mass index (BMI) z 25 kg/m2 in 1982, 1985, and 1995; Never overweight, BMI < 25 kg/m2 in 1982, 1985, and 1995; Sometimes overweight, BMI z 25 kg/m2 in 1982, 1985, or 1995. Physical activity classifications: Always active reported z1000 kcal/week in 1982, 1985, and 1995; Never active reported <1000 kcal/week of activity in 1982, 1985, and 1995; Sometimes active reported z1000 kcal/week of activity in 1982, 1985, or 1995 (* indicates bars where n < 10).

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Table 3 Hierarchical multiple linear analysis predicting physical function as measured by the Functional Status Questionnaire and gait speed in 1999 from physical activity and body mass index (BMI) from 1982 to 1995, adjusting for age and the presence of chronic conditions (n = 156) Model 1

Model 2

Model 3

Beta

Beta T

Beta

T

T

Dependent variable—Functional Status Questionnaire BMI (1982, 1985, 1995) 3.25 2.17* – – Physical activity – – 4.93 2.58* (1982, 1985, 1995)

2.58 4.26

1.71 2.20*

Dependent variable—gait speed (m/s) BMI (1982, 1985, 1995) 0.04 2.43* – – Physical activity – – 0.07 3.15* (1982, 1985, 1995)

0.03 0.06

1.91 2.75*

Functional Status Questionnaire—Model 1: adjusted R 2 = 0.06, F = 4.51, P < 0.005; Model 2: adjusted R 2 = 0.08, F = 5.19, P < 0.002; Model 3: adjusted R 2 = 0.09, F = 4.68, P < 0.001. Gait speed—Model 1: adjusted R 2 = 0.14, F = 9.61, P < 0.0001; Model 2: adjusted R 2 = 16, F = 11.14, P < 0.0001; Model 3: adjusted R 2 = 18.0, F = 9.41, P < 0.0001. * P < 0.05.

Longitudinal analyses (1982 –1999) Physical activity participation from 1982, 1985, and 1995 as reported on the questionnaire was related to physical function in 1999 (Fig. 1). Women who reported >1000 kcal/week of physical activity in 1982, 1985, and 1995 (i.e., always active) and who had a BMI < 25 in 1982, 1985, and 1995 (i.e., never overweight) reported less difficulty with ADL and walked faster than women who were inactive or who were overweight/obese at any of the time points. Women who were never active and always overweight reported the greatest amount of ADL difficulty and walked at the slowest gait speeds. Women who were always active but always overweight reported less ADL difficulty than women who were never active and never overweight. To identify which factors (weight and physical activity) best predicted physical function in 1999, hierarchical linear regression was used. After controlling for age and the presence of chronic conditions, both weight (model 1) and physical activity (model 2) were significant independent predictors of physical function (i.e., FSQ score and gait speed) in 1999 (Table 3). When both weight and physical activity were simultaneously entered into the model (Model 3), physical activity was the only significant independent predictor of physical function (i.e., FSQ score and gait speed) in 1999 (Table 3). Age, presence of chronic conditions, weight, and physical activity accounted for 9% of the variance in FSQ score and 18% of the variance in gait speed in 1999. First-order interactions between the presence of chronic conditions and body weight and physical activity were not significant.

Discussion Our findings that obesity is related to physical function in older women confirms the results of previous research [7– 10]. The fact that physical activity is related to physical function has also been shown [12 – 22]. Interestingly, in this study, overweight and obese older women who are active have levels of physical function similar to that of older women who have normal weight. Therefore, physical activity appears to be as important if not more important than body weight in predicting physical function. Our findings support the idea that ‘‘fitness’’ is more important to health outcomes than ‘‘fatness’’ [38,39]. It appears that fitness may be more important to health outcomes than body weight as is evident from the recent research that has shown that unfit lean men were at greater risk for all-cause mortality and cardiovascular disease mortality than men who were fit and obese [38]. Researchers have also shown that independent of changes in body weight, improvements in cardiovascular fitness are related to a decreased risk of cardiovascular disease [39]. Our research is unique in that our outcome of interest is physical function and not cardiovascular disease, diabetes, or mortality. Our research is also different in that we examined physical activity instead of physical fitness. LaCroix et al. [19] examined the association among smoking, alcohol consumption, physical activity, and body mass index to maintaining mobility in late life. They found that regular physical activity was associated with a 40% decreased risk of losing mobility, where as obesity was associated with a 20–40% increased risk of losing mobility. They also concluded that physical activity and not BMI appears to have the greatest potential to reduce disability in late life [19]. Both obesity and physical activity may affect physical function through their relationship with chronic conditions. Both obese and inactive persons are at higher risk for chronic conditions such as heart disease and osteoarthritis and the presence of these chronic conditions is also related to impaired physical function [40 – 44]. Physical activity may prevent impairments in physical function by preventing the chronic conditions related to impaired physical function. In addition, physical activity is related to strength, balance, and aerobic capacity, all important factors in the preservation of physical function [13]. The long-term follow-up and high participant retention are two major strengths of this investigation. We were able to determine the vital status of 219 of the participants (96% of the original sample) and we had complete physical function measures on approximately 75% of the original sample. This research is unique in that the women were followed for an extended period of time, 17 years, compared to previous studies, which have examined the short-term association among physical activity, obesity, and physical function [8,10,22]. One limitation of this research is the relatively homogenous sample of woman. Most of the participants were of upper social economic status and Caucasian as determined at

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the initiation of the randomized trial in 1982. The homogenous nature of our sample does limit the generalizability of our findings. However, the similarity of the participants could also be viewed as a strong point, in that the number of potential confounding factors such as race or social economic status was reduced. The outcome of interest, physical function, was not measured at the initiation of the original clinical trial (1982 –1985). Therefore, it is unclear if the women had any limitations in physical functioning that may have prevented them from being physically active. However, it is reasonable to assume that the women were free of functional limitations at the start of the trial since they were not eligible to participate unless they were free from limitations that would preclude them from exercising. In the women who were overweight/obese, the women who were physically active had better physical function than those who were inactive. The results suggest that interventions focused on behavioral changes such as increasing physical activity may be beneficial to the prevention of decline of physical function in older adults. Given that both unintentional [7,45] and intentional [46 – 48] weight loss may be detrimental to health in older persons, it may be best to focus on increasing physical activity rather than weight loss. Obesity and physical inactivity are prevalent problems in the United States, especially in older adults. Twenty-five percent of the people between the ages of 60 and 69 are obese and 17% of the people over 70 are obese [1]. Physical inactivity is an even larger epidemic with 30–35% of men and women 65–74 years of age and 38–50% of mean and women 75 years of age or older reporting no participation in leisure-time physical activity [29]. Given the benefits of physical activity to health and the prevalence of inactivity among older adults, it may be advantageous to switch some of the focus of the public health efforts to promoting physical activity.

Acknowledgments This study was funded by a grant from the National Institute on Aging (Grant AG14753). At the time this work was completed, Jennifer S. Brach was funded in part by the National Institutes of Health (Public Health Service Grant TG32AG00181), the Foundation for Physical Therapy, and the Geriatric Section of the American Physical Therapy Association.

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