Physical activity of adult Australians: Epidemiological evidence and potential strategies for health gain

Physical Activity of Adult Australians: Epidemiological Evidence and Potential Strategies for Health Gain* Adrian Bauman I & Neville Owen 2 1Univeristy Of N e w South Wales, 2Deakin University * Paper based on both authors' Keynote Addresses tO the XXth Australian Conference on Science and Medicine in Sport, Canberra, 1996.

Bauman, A., & Owen, N. (1999). Physical activity of adult Australians: Epidemiological evidence and potential strategies for health gain. Journal ofSdence and Medicine in Sport 2 (1): 30-41 Physical activity is now considered a major modifiable factor for preventing and reducing the mortality from cardiovascular disease, diabetes and some cancers, as well as improving musculoskeletal and mental health. Increasing epidemiological evidence conftrms the health benefits of moderate regular physical activity. A dose response relationship remains, with greater benefits derived from increased intensity and duration of physical activity. Clinicians and exercise scientists should consider physical inactivity as important a risk factor as hypertension or elevated serum cholesterol levels. The broader public health objectives are to measure and monitor physical activity levels among all Australians, and to develop interventions to increase regular participation for the whole population. Population Campaigns and behaviour change programs are needed to increase the prevalence of participation in physical activity.

Introduction This p a p e r presents the recent epidemiological evidence for the health benefits of physical activity. In addition, we review the prevalence of participation in physical activity in Australia, and w h a t is known a b o u t the impact of large-scale campaigns. Our purpose is to increase exercise scientists' and clinicians' awareness of the evidence for the health benefits of regular moderate intensity physical activity, and to indicate population-wide approaches to increasing physical activity participation. The health benefits of physical activity have achieved international recognition following the publication of the 1996 US Surgeon General's Report on Physical Activity and Health (United States Department of Health and H u m a n Services [USDHHS] 1996). Despite over a decade of evidence (Powell et al., 1987), the promotion of physical activity and its inclusion in public health approaches to prevention h a s lagged behind other 'established' disease risk factors. Given the high prevalence of inactivity, the population importance of increasing physical activity appears to be at least as important in coronary heart disease prevention as efforts to reduce high cholesterol or high blood pressure (Fletcher, 1995; Blair, 1995). In addition, there are a range of other health benefits which include diabetes prevention and control, aspects of injury and falls prevention, mental health promotion, and a favourable impact on some cancers, especially colon cancer (USSG, 1996). 30

PhysicalActivityof AdultAustralians:EpidemiologicalEvidence...

New Epidemiological Evidence on Physical Activity and Health The quality of epidemiological evidence Most of the epidemiologlcal evidence e m a n a t e s from good quality observational (cohort) studies. Thus, there is little randomised controlled trial evidence, b u t this is the same quality of evidence as for the risks of active smoking, where the health risk is widely accepted. As with exposure to smoking, it would now be very difficult to conduct a controlled trial at the population level, as there would be substantial crossover (from the allocated physical activity group to the controls and vice versa, reducing the power of the study, or increasing the required sample size to unrealistic levels). The strength of the epidemiological evidence for physical activity is enhanced by the consistency of the observed benefits across studies. Despite various m e a s u r e s of exposure (physical activity, fitness, motion sensors), the association between inactivity a n d disease outcomes remains remarkably consistent. Recent studies have adjusted for confounding variables, and demonstrate that the effects of physical activity are independent of other risk factors such as hyperlipidemia, hypertension or obesity. Finally, the reviews of the evidence have shown a greater association between physical activity and health outcomes where the research design and methods are optimal (Berlin & Colditz, 1990; Powell, 1987) further suggesting the relationship is likely to be causal. The overall epidemiological evidence is considered good to excellent, as suggested by the recognition it is now receiving internationally. Physical activity and overall mortality The effects of physical activity on reducing the risk of all cause mortality are consistent and strong (Kampert & Blair, 1996; Lee & Paffenberger, 1997). These associations are generally stronger for m e a s u r e d cardio respiratory fitness t h a n for reported physical activity, particularly for women. Different types of physical activity, even including stair climbing, of at least 20 flights per week, appear to confer a benefit on all cause mortality (Paffenbarger, 1994). The relationship between physical activity and all cause mortality is present for all age groups, and longitudinal data suggest that there is a reduced risk of mortality even amongst adults who adopt physical activity later in life (Blair, 1995; Lindsted, 1991). Furthermore, an increase in physical activity a m o n g middle aged m e n and women appears to confer a subsequent health benefit, within two or three years, in t e r m s of overall risk of death (Paffenbarger, 1993; Blair, 1995). Longitudinal studies among diverse populations s u c h as US college alumni, British civil servants, US Seventh Day Adventist men, Alameda County (California) residents, US railroad workers, Dallas m e n and women, Finnish populations, m e n in the British Regional Heart Study and others have shown that physical activity extends life (USSG, 1996). Recent evidence h a s b e e n provided to suggest a 50% decrease in all-cause mortality a m o n g 41,000 moderately active postmenopausal women, further suggesting a similar protective relationship for women (Kushi, 1997). Effects upon coronary disease incidence and mortality The strongest evidence for physical activity is in the prevention of cardiovascular disease. Studies have repeatedly shown that those who are sedentary have a 1.5 to twofold increase in the risk of incident or fatal cardiovascular events, compared

31

Physical Activity of Adult Australians: Epidemiological Evidence...

to those who are at least moderately physically active (Berlin & Colditz,-1990; USSG, 1996). Consistently across studies, the m a x i m u m cardiovascular disease benefit occurred in moving from sedentary or low fitness groups in the population to moderate activity or moderate fitness levels (Blair, 1995; Lakka, 1994). There is evidence of a dose response relationship with more sustained activity conferring greater reduction in the risk of fatal and nonfatal coronary events. There are biologically plausible m e c h a n i s m s for this observation (Haskell, 1994), including some angiographic evidence of reversal of coronary atherosclerosis following prolonged exercise (Hambrecht, 1993). The CHD and all cause mortality benefits of activity are s u m m a r i s e d in Table 1, which s u m m a r i s e s recent epidemiological studies since 1995, following the US Surgeon General's Report. The table shows whether the m e a s u r e m e n t of exposure was by self reported physical activity or used a standardised m e a s u r e of fitness. The outcomes were incident or fatal CHD, or all cause mortality (most of which were CHD). The relationships are expressed in terms of relative risk of the outcome in the least active/least fit, compared to the m o s t active/most fit. Table 1:

Key epidemiological studies since 1995- evidence for health benefits of physical activity upon all cause or cardiovascular mortall~

Author (Year)

Sample size

Design & follow-up

Study Factor

Outcome Factor

Blair 1995

9770 US M

Cohort, 5 yr

fitness

CVD deaths

**

Fried 1998

5885 US adults 65 yrs+, M & F

Cohort, >5 yrs

lifestyle PA self report

all cause deaths

**

Woo 1998

Older Chinese adults 70+ yrs

Cohort 1.5yrs

self report PA index

all cause deaths

**

Kujala 1998 aged 25-64

Finnish twins 17 yrs

Cohort LTPA

self report deaths

all cause ** regular PA

* occasional PA

Morgan K 1997

UK older adults 65 yrs+

Cohort 10 yrs

self report usual PA

survival function

* intermediate PA ** high level PA

Rosengren 1997

7412 middle aged US adults

Cohort 20 yrs

work PA & LTPA

CHD deaths all causedeaths

* *

Leon 1997

MRFtT study 12318 males

Cohort 16 yrs

LTPA

CHD deaths * all causedeaths *

Haapanen 1997

2840 Finnish M&F

Cohort 10 yrs

LTPA

CHD incidence hypertension

** (M), 0 (F) ** (M) 0 (F)

642 older Swedish males

Cohort 25 yrs

LTPA 4 categories

all causedeaths vasculardeaths

* *

Hedblad 1997

Magnitude of association

Legend Measure of exposure: PA physical actMty by self report/interview Fitness: estimate of V02 max or submaximal test data Measure of outcome: CVD, CHD: cardiovascular or coronary heart disease mortality, all cause mortality 32

Magnitude Of association: comparing inactive to physically active group [usually adjusted for other potential confounders] 0 no significant association * **

Odds ratio 1.0-1.5 Odds ratio 1.51-2.0

PhysicalActivity of Adult Australians: Epidemiological Evidence...

The associations in Table 1 and in the USSG report appear strong, irrespective of whether self reported physical activity or objectively measured cardiorespiratory fitness are the exposure measure. Over the past three decades of research, this relationship has appeared consistently across a range of outcomes, including incident coronary heart disease, fatal and non fatal coronary heart disease, and incident and fatal myocardial infarction rates. The recent studies summarised in Table 1 show very similar results to the USSG report. Typically the relative risk between the most active and the least active suggests that there is about twice the risk of all cause cardiovascular incident events or mortality in the least active compared to the most active segments of the populations studied (Berlin & Colditz, 1990; Powell, 1987). Stroke The relationship between physical activity and the prevention of cerebrovascular disease (stroke) is made more difficult due to different pathophysiological mechanisms for stroke. Recent studies have produced some encouraging results, with an inverse association between physical activity and risk of (ischaemic) stroke (Shinton, 1993; Wannamethee, 1992). The mechanism may be protection against blood clot formation and, hence in reducing thrombosis. An alternative protective mechanism may be mediated through the effects of physical activity upon high blood pressure (Fagard, 1994). Effects upon o t h e r cardiovascular risk factors The physical activity and CHD studies show that the effects of physical activity or fitness persist after statistical adjustment for the effects of other cardiovascular risk factors (Powell, 1987; Berlin, 1990; Paffenbarger, 1993). Further, physical activity appears to have a direct role in the improvement of other CHD risk factors (Bauman 1991). These include cross sectional and longitudinal associations with blood pressure, body mass index and HDL/total cholesterol (Young, Haskell 1993). There is some evidence for an effect on high blood pressure, with a meta analysis (Kelley, 1994) suggesting that vigorous physical activity and exercise decrease systolic and diastolic blood pressure by approximately 6-7 ml Hg. Further, there is some evidence that moderate physical activity may produce a greater decrease in systolic blood pressure than high intensity physical activities (USSG, 1996). Physical activity also has a role in improving lipid profiles, particularly the HDL sub fraction (Moore, 1994). More sustained and vigorous physical activity has a place in weight control and weight maintenance, as an adjunct to and independent of dietary restriction (Blair, 1994). Another proposed set of risk factors for acute cardiac events are associated with fibrinolytic activity. In a recent population study in Sweden (Eliasson, 1996) physical activity was associated with increased fibrinolytic activity, providing another putative biological mechanism for the acute health protective benefits of physical activity. Cancer prevention There are n u m e r o u s studies examining the relationship between physical activity and colon cancer. Almost all of the more than 30 studies show a protective effect (USSG, 1996; Slattery, 1997; Colditz, 1997). Recent studies have shown this to extend to preventing precancerous polyps in the large bowel (Neugut, 1996; Slattery, 1997). Plausible biological mechanisms have been proposed, including effects on prostaglandins and antioxidants, reduced intestinal transit time, and a contribution to overall energy balance (Slattery, 1997). 33

PhysicalActivity of Adult Australians: Epidemiological Evidence.,. Several studies have reported a protective effect with respect to breast cancer. A recent large cohort study in Norway showed a 30% decrease in risk of bi-east cancer, particularly among younger women aged less t h a n 45 years (Thune, 1997). Another recent study used a case-control methodology, and showed a protective effect of moderate occupational physical activity upon the risk of breast cancer (Coogan et al., 1997). There are too few studies to m a k e clear statements about uterine cancer or ovarian cancer and physical activity. There are a n u m b e r of studies of physical activity and the risk of prostate cancer in men. Some of these studies show a significant inverse relationship, particularly for older men. A recent cohort study of Iowa m e n showed a marginal protective effect of high levels of activity compared to the sedentary, b u t no dose response relationship nor biological m e c h a n i s m s were proposed (Cerhan, 1997). Overall these findings warrant further epidemiological investigation. Diabetes: primary prevention and control The increasing incidence of Non Insulin Dependent Diabetes Mellitus (NIDDM) is a cause for concern, especially a m o n g older adults, some migrant populations and a m o n g Aboriginal populations. There is good evidence that physical activity has a role in the control of and primary prevention of NIDDM. The most compelling evidence has come from population based cohort studies, where risks of developing diabetes are lower in those who are physically active, even adjusting for body m a s s index (Helmrich, 1994; Manson, 1991). Between a third and a half of new cases of diabetes might be prevented by regular moderate physical activity. Secondary prevention is also important. For those who have diabetes, physical activity m a y improve glucose metabolism, increase insulin sensitivity, and also prevent the increase in atherosclerotic disease a m o n g those with diabetes. A large recent cross sectional study showed that quality of life and mental health was highest a m o n g diabetics who were physically active, after adjustment for other confounding factors (Glasgow, 1997). Arthritis and osteoporosis There is a complex relationship between osteoarthritis and physical activity. In some studies, particularly amongst athletes and sports participants, the risk of osteoarthritis m a y be greater for those who participated at an elite level. The site of the osteoarthritis m a y also reflect joints subject to repeated injuries or over used in sports. For people in the general population with osteoarthritis or rheumatoid arthritis, there is some evidence that moderate activity relieves symptoms, possibly reduces joint swelling, and is associated with improved psycho-social and ftmctional status (Minor, 1991). Osteoporosis is characterised b y decreased bone m a s s and deterioration of bone tissue, leading to increase likelihood of fractures. Physical activity m a y theoretically ameliorate osteoporosis through increasing bone m a s s by being active during adolescence, and by preventing a reduction in bone m a s s during mid life. The development of osteoporosis and subsequent bone fracture has been shown to be associated with physical inactivity (Drinkwater, 1994). Weight bearing activity during adolescence h a s been shown to be important for the development of peak bone m a s s (Welten, 1994). The American College of Sports Medicine (ACSM) position statement on osteoporosis (ACSM, 1995) concluded that fimctional loading through physical activity exerts a positive influence on bone m a s s , b u t the types of programs that m a y be most effective in producing beneficial results are still uncertain.

34

PhysicalActivity of Adult Australians: Epidemiological Evidence...

Participation in physical activity in older adults can help maintain mobility and independence and decrease the risk of injury, fracture or physical impairment (Simonsick, 1993). Regular physical activity can favourably impact on important physical factors predisposing to falls: including balance, muscle strength and osteoporosis (Lord, 1994; 1995). Physical activity also appears to reduce the risk of hip fracture in men. Mental health Mental health benefits of physical activity are based on cross sectional survey associations, as well as on clinical trials where PA has been consistently shown to be associated with lowered levels of stress and anxiety across many studies, and irrespective of the measurements of anxiety and stress used (PetruzeUo, 1991). Physical activity has been associated with better indices of mental health in population studies (Stephens, 1988; Simonsick, 1991), as well as being a recognised and evidence-based treatment for clinical anxiety and depression. In other studies, physical activity is associated with self-esteem, improved mood and measures of well being (McAuley, in Bouchard 1994). Those who are less active or less fit are known to be more anxious a n d / o r depressed (Brill, 1992). The dose, frequency and nature of the relationship between physical activity and mental health remains to be further clarified. Risks of physical activity Two major areas of risk exist for participation in physical activity. The first is the risk of injury, especially muscuoloskeletal injuries. The most frequent set~ngs for these injuries are in competitive sports (overuse injuries) or in untrained sedentary individuals who embark upon sudden vigorous physical activity. The second area of risk is acute cardiovascular events during participation in physical activity. Although the risk of cardiac events is higher among those who are vigorously active, this increase in risk is far outweighed by the net benefit of being active for that individual (i.e. overall individual and community risk is reduced, even for vigorous physical activity participation). This is described in detail elsewhere (Thompson, 1994; Siscovick, 1984).

The Need to Understand and Influence the Physical Activity Levels Of Adult Australians Information on the physical activity habits of the population is an essential prerequisite for community wide exercise promotion efforts, for the planning of sport and recreation facilities and for other innovations to support community physical activity. Government expenditure on sport and recreation is significant (estimated to have been some $2,100 million in 1989-90), and such expenditure is often justified, at least in part, by a physical activity and health rationale. Recent research papers and reports using Australian population data have examined the prevalence and trends in physical activity participation during the 1980s and 1990s (Bauman, et al., 1990; National Heart Foundation, 1989; Owen & Bauman, 1992). These research reports have assessed characteristics related to participation (Booth et al, 1993; Commonwealth Department of Sport, Environments, Tourism and Territories 1992, 1995; Owen & Bauman, 1992), and documented the reliability and validity of self-report measures of physical activity used in population surveys (Bauman & Owen, 1991; Booth et al, 1996a,b; Gore et al, 1993), the effectiveness of recent Australian campaigns (Booth et al, 1992; Owen et al, 1995) and the applications of these recent findings for public-health 55

Physical Activity of Adult Australians: Epidemiological Evidence...

intervention strategy and policy development (DEST, 1995; Donovan & 0wen, 1994; Owen, 1994, 1996; Active and Inactive Australians, 1995). Prevalence is ideally assessed from representative population surveys. For example, during the 1980s, surveys asked respondents about their physical activity behaviours during the preceding two weeks (Owen & Bauman, 1992). Self reported physical activity was preferred to more objective physiological methods of assessment such as oxygen uptake estimates, direct/indirect calorimetry or motion sensors, which may not be practical in epidemiological research. These self-reported activity data enabled the construction of a physical activity index which estimated leisure time energy expenditures [Bauman, 1987] . This index was based on the type of activity reported, and the frequency, duration and intensity of that activity within the previous two weeks. The index was categorised into four discrete levels of physical activity. These were: (i) vigorous activity meeting the 'aerobic' criteria of the American College of Sports Medicine, (ii) moderate physical activity; (iii) low level activity; and (iv) sedentary, or physically inactive individuals. The Commonwealth Department of Sport conducted representative population surveys with data from 17053 individuals between 1984 and 1987. The proportions in the different categories of physical activity were: 15% reported vigorous physical activity ('aerobic' category); 19% were moderately active; 36% reported low-intensity or infrequent physical activities (such as gardening, bowling, sailing); and, 30% were totally sedentary. Repeated population surveys conducted in the mid-1980s (Owen & Bauman, 1992) identified characteristics of those least likely to be active. Women, financially and educationally disadvantaged, older adults, and those from a nonEnglish speaking background were least likely to be sufficiently physically active for a health benefit. The most frequently performed moderate-intensity and vigorous physical activities were non-organised forms of activity, including walking, jogging, cycling, swimming, and callisthenics/aerobics classes, as shown in Table 2. National data from the mid 1980s are compared with a more recent survey confmed to NSW in 1996, where more moderate activity such as gardening was also asked. No direct comparisons are possible for trends, b u t non-organised physical activities, in both surveys, were the most frequently reported by Australian adults. Data on trends in physical activity participation in Australia are limited, and trend data should be interpreted with caution if surveys have used different methods and questions. The 1980s prevalences referred to above were derived from surveys conducted by telephone. Similar prevalence rates are apparent from preliminary analyses of questions from the 1 9 8 9 / 1 9 9 0 and 1 9 9 5 / 1 9 9 6 household interview National Health surveys, suggesting limited changes in prevalence since the 1980s (Australian Institute of Health and Welfare, unpublished observations). A recent report of possible increases in reported walking since 1990 may be limited by these methodological constraints (Abraham et al., 1995). It is essential to use standard methods for assessing and monitoring trends in physical activity by self report surveys. A national physical activity monitoring system is urgently needed for this purpose. Recent measurement issues include the need to better assess incidental physical activity, as well as occupational and domestic physical activity levels. This encompasses many of the forms of physical activity at work, at home, and activity in which people take part as they go about their day-to-day lives, generally

36

Physical Activity of Adult Australians: Epidemiological Evidence... Table2:

Most frequent physicalactivities reported by adult AustraliansLPrevelenceof all major physicalactivities in prevfous2 weeks (1984-1987,nationalpopulation samples)comparedwith leadingrep(~rtedmoderate and vigorousactivities in the previousweek. (1996New South Walespopulationsample)

National Australian data 1984-1987 (n=17053) surveyed across all seasons Most frequently Participation Participation reported sport (%) Vigorous (%) Moderate & recreational actMty Walking

10

32

Swimming Callisthenics, aerobics Cycling Jogging Football Jail] Golf Tennis Squash other sport

5 5

13 8

3 4 2 0 2 2 2

7 6 6 6 6 2 2

NSW adult physical activity survey (n=3392) surveyed in July 1996 l~/pos of Activity

Participation (%) Vigorous

walking exercise 15 /recreation Swimming 3.5 Gym work, weights, 11.5 aerobics classes Cycling 2.6 Jogging, running 6.2 Soccer,football 6.5 Golf n.a. Tennis 6.2 Digging, heavy work 2.5 Gardening, n.a. lawnmowing

Participation (%) Moderate

33 1.4 1.7 1.0 n.a 0.7 5.3 n.a. 1.4 32.7

n.a. not availableor not categorisedas moderate or vigorous in the survey

using large skeletal muscle groups. Incidental activity can involve using stairs instead of lifts or escalators, riding a bicycle rather t h a n driving a car to do minor errands, or choosing not to use energy-saving implements for domestic tasks. Improvements in the measurement of these phenomena will contribute to a better understanding of physical activity that enhances public health.

EffOrtS to Increase Participation in Physical Activity at the Level of the Whole Population There are a range of methods to increase physical activity in Australia, ranging from individual counselling, group programs, worksite and school programs, and whole population campaigns. A recent review found few examples of national efforts and public education campaigns (King, 1991). In Australia, national physical activity campaigns were conducted by the National Heart Foundation of Australia (NHF) in 1990 (Exercise: make it part of your day; Booth, Bauman, Oldenburg, Owen & Magnus, 1992) and 1991 (Exercise: take another step; Owen, Bauman, Booth, Oldenburg & Magnus, 1995). The campaigns were informed by social-learning and social-marketing models, and each emphasised walking as the main activity. The media campaigns were supported through media news coverage and through local level community-based promotional activities and events. These Australian campaigns provided an opportunity to examine the effects of serial national mass-media campaigns to promote physical activity. The 37

Physical Activity of Adult Australians: Epidemiological Evidence...

evaluation of the 1990 campaign (Booth et al., 1992) found increases in the prevalence of reports of walking following the campaign. Changes were most marked in older people, a n d occurred across most socio-economic groups, Awareness of the campaign message increased significantly from before the first campaign to after that campaign (46% to 71%). Changes in awareness and in reported walking for exercise and in readiness to exercise reported in 1990 were not found following the 1991 Campaign (Owen et al., 1995). The limitations of m a s s m e d i a in changing health-related behaviours have been discussed elsewhere (Redman et al., 1990). Future campaigns are planned through the Active Australia framework, with a m u c h longer timescale, and an integrated whole-of-government approach to programmatic activity.

Making use of Research and Making a Difference to Public Health In s u m m a r y , there is significant potential for population health gain if more Australians became physically active. This potential gain is of the same magnitude as other population health efforts to control hypertension or elevated cholesterol levels, and only slightly less likely to impact u p o n health t h a n tobacco control. The relative importance of physical activity is now identified, both in physical activity reviews (USSG, 1996) and in general reviews of the major contributors to mortality, where improvements in physical activity are recognised as a major contributor to health. Despite this extensive body of data, physical activity h a s been under-recognised and h a s received less attention as a public health imperative t h a n have other modifiable health risks. The challenge is to translate this new evidence into policy and programs at the population level. The long t e r m objective is to implement integrated and multisectoral strategies that increase physical activity, in collaboration with partners from beyond the health sector (Bauman, Bellew et al., 1996). These include recreation-sector professionals, educators, and those in u r b a n planning, transport, environmental design and local government. An important current investment by the health sector through the Australian Institute of Health and Welfare is the establishment of standardised population-level physical activity monitoring systems and the support of well-designed evaluations of m a n y of the programs and campaigns now emerging u n d e r the "Active Australia" banner. Repeat population surveys will provide evidence of the effectiveness of these strategies. Increases in the prevalence of physical activity across the whole Australian population will be the key outcome indicator.

Acknowledgments ABS National Health survey 1995/6; NSW Health Physical Activity survey 1996.

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