Physical Activity and Years of Healthy Life in Older Adults
Physical Activity and Years of Healthy Life in Older Adults: Results from the Cardiovascular Health Study
Calvin H. Hirsch, MD[1], Paula Diehr[2], Anne B. Newman, MD[3], Shirley A. Gerrior, Ph.D [4], Charlotte Pratt, PhD[5], Michael D. Lebowitz, MD[6], Sharon A. Jackson, PhD[7]
for the
Cardiovascular Health Study Research Group
Funding sources: Contracts N01-HC-35129, N01-HC-45133, N01-HC-75150, N01-HC-85079 through N01-HC-85086, N01 HC-15103, N01 HC-55222, and U01 HL080295 from the National Heart, Lung, and Blood Institute, with additional contribution from the National Institute of 0Neurological Disorders and Stroke.
Presented in part at the national meeting of the American Geriatrics Society, May, 2006
ABSTRACT
Objective: To determine the number of years added toassociated with survival and disability-free years by at different levels of physical activity (PA) in older adults from different age groups.
Design: Longitudinal cohort study.
Participants: 5,392 participants of the Cardiovascular Health Study.
Measurements: We assessed the independent contribution of self-reported PA to survival and years with self-reported good or better health over 11 years, and to years free of disability over 6 years. Quintiles of PA, measured in kcal/week, were established for 3 age groups: 65-69, 70-74, and > 74. MultivariateMultivariable linear regression adjusted for a wide array of demographic and health-related variables.
Results: At baseline, participants’ mean age was XX (range: XX-YY), xxxx (XX%) were men, and xxxx (XX%) reported dependence in ( 1 IADL. [RESULTS NEED TO BE UPDATED BASED ON THE EVALUABLE SAMPLE OF 5392.] Survival averaged 9.96 (( 2.34) [Note. This is a standard error. Elsewhere in the paper, the quantity in parentheses represents a standard deviation. I suggest that you present a confidence interval here (9.6-1.96*2.34, 9.6 + 1.96*2.346 here, and explain elsewhere that you mean standard deviation]. years for participants aged 65 to 69 and 8.09 (( 3.31) years for those over age 74. Compared to the least active quintile after adjusting for covariates, PA had no significant impact on survival in the 2 younger age groups. Among participants > age 74, those in the most active quintile lived 1.02 (± 0.22) years longer than those in the least active quintile (p < .001). PA increased disability-free years for ADL, IADL, and mobility in subjects aged > 69. Compared to the least active quintile, disability-free years increased with higher activity and age, but only slightly (≤ 1.01 years).
Conclusions: The increased longevity and years of healthy life conferred byassociated with higher physical activity accrue mostly to persons over age 74.
(250 words)
Key words: Aging, Exercise, Mortality, Activities of Daily Living, Mobility Limitation
INTRODUCTION
It is well-established that a physically active lifestyle is associated with a reduced risk of mortality in middle-aged adults. This mortality benefit appears remarkably stable over time, persisting for 16 years among men and women in the Framingham heart Study cohort and 22 years among male participants of the Harvard Alumni Health Study. (Lee, 1992; Lee 2000; Sherman 1994a) Among the middle-aged, the reductions in mortality correlate in a dose-response fashion with the energy consumed in intense physical activities or with exercise capacity, with negligible benefit from non-vigorous activities, regardless of the net energy expended . (Lee, 1994; Gulati, 2003) Epidemiologic studies focusing on persons over age 65 likewise have demonstrated a reduced risk of mortality in those who are physically active compared to being sedentary.(1-11) Although the studies differ in the ways they assessed physical activity and defined a physically active lifestyle, overall they demonstrate that older individuals need to perform less vigorous physical activity than middle-aged adults to achieve a significant reduction in mortality risk.
In middle-aged and older adults, regular physical activity also protects against functional decline and the development of disability.(5, 8, 12-19) Consistent with the pathway of disablement hypothesized by Verbrugge and Jette,(20) physical activity’s ability to prevent disability appears to derive from its ability to reduce the development of functional limitations.(8) In an older cohort (median age = 70), Tager et al. showed that high levels of leisure-time physical activity independently protected against the development of severe functional limitations in men. In women, however, their results suggested that physical activity reduces the risk of severe functional limitation by its effect on the proportion of lean body mass to fat mass. (18)
Although higher levels of physical activity reduce the risk of dying and functional decline, compared to staying sedentary, there has been little effort to date to translate the impact of a physically active lifestyle into the actual number of years it can increase survival or years free of functional limitations. Using data from the Framingham heart study, Franco et al. calculated mean life expectancy after age 50 from the hazard ratio for mortality, stratifying by level of physical activity.(21) However, the comparative benefits of physical activity for survival and disability-free years, compared to being sedentary, have not been established in older adults from different age groups. To ascertain this, we utilized 11 years of follow-up data for survival and self-rated health, and 6 years of follow-up data for disability from the Cardiovascular Health Study, a population-based cohort study of men and women aged 65 and older at study entry.
METHODS
Study Cohort
The Cardiovascular Health Study (CHS) is an ongoing, observational, population-based cohort study of persons aged 65 and over recruited from 4 communities in the United States: Sacramento County, California; Allegheny County, Pennsylvania; Forsyth County, North Carolina; and Washington County, Maryland. CHS supplemented the original cohort of 5,201 men and women, which was enrolled between 1989 and 1990, with an additional 687 African-Americans during the 4th study year (1992-1993). Details of the study design are described elsewhere. (3, 22)
Data Collection
Using standardized questionnaires and procedures, trained technicians collected demographic and psychosocial information; data on health habits; a standardized medical history for selected conditions and current medications; objective cardiovascular data; reported and objective measures of physical performance; data on affective state and cognitive functioning; and blood samples for a variety of laboratory analyses performed at the Laboratory for Clinical Biochemistry Research at the University of Vermont. Participants returned for annual clinic visits and underwent telephone interviews 6 months after each visit through 1999. Limited telephone surveillance for study outcomes has continued since 2000. Deaths initially were identified by interview with an informant and listings in obituary columns, and later confirmed by reviewing medical records, death certificates, and the HCFA health care utilization database for hospitalizations. There has been 100% ascertainment of participant mortality.
Variables
Outcome variables: Our outcomes of interest were the average number of additional years of life and years of healthy life (years in good, very good, or excellent health) self-reported healthy life (SRHLYHL), over 11 years of follow-up, conferred byassociated with being physically active compared to being sedentary at study entry. [I strongly prefer years of healthy life and YHL because it’s what I (and a few others) have always used.] Additional outcomes included average additional years free from disability over 6 years of follow-up as a result of physical activity. We defined SRHL as good to excellent versus fair to poor self-reported health. Disability in activities of daily living (ADL) was defined as any reported difficulty walking around the home, getting out of bed, eating, dressing, bathing, or using the toilet. We defined disability in instrumental activities of daily living (IADL) as reported difficulty performing heavy housework, doing light housework, shopping, preparing meals, paying bills, or using the telephone. We defined upper-extremity disability as reported difficulty lifting, reaching, or gripping. Mobility disability was defined as reported difficulty walking ½ mile or ascending 10 steps.
Predictor variable: The principal predictor variable was the energy in kilocalories (kcal) consumed in weekly leisure-time physical activity plus household chores estimated from the Minnesota Leisure Time Activities Questionnaire, which was based on the 2 weeks prior to the baseline visit.(23) [Did we ever consider a combined outcome, for years without any of those problems? I guess it would be hard to explain. But we did do this on a different paper for several measures of balance].
Analytic approach
For theseThese analyses, we merged data from include both the original and African-American cohorts. [A lot of this seems to be understandable only by CHS people. For others, it is TMI (too much information). We used multivariatemultivariable linear regression to assess the independent contribution of baseline physical activity to each of the outcome measures. Participants were divided into 3 age groups: 65-69, 70-74, and ≥ 75. Physical activity in kcal was divided into age-category-specific quintiles, with participants in the lowest quintile serving as the reference group. Participants were divided into 3 age groups: 65-69, 70-74, and ≥ 75. For each outcome, separate regressions were run for the 3 age groups. As potential confounders, we selected variables that previously had been shown to predict 5-year mortality in the CHS.(24). We also selected variables which had a univariatebivariate association with one or more of the functional outcome measures or which plausibly could contribute to functional impairment. Covariates included demographic and personal characteristics, reported chronic illness such as arthritis, established risk factors for cardiovascular disease (CVD) such as smoking and hypertension, assessed subclinical CVD (e.g., ankle-brachial index, internal carotid wall thickness), inflammatory markers, adjudicated prevalent cardiovascular disease and congestive heart failure, depressive symptoms measured by a 10-item version of the Center for Epidemiological Studies depression questionnaire (CES-D),(25) historical physical activity, and age-gender interaction term, and cognitive function measured by the Digit Symbol Substitution Test(26) plus the Mini-Mental State Examination (MMSE).(27) Because the CHS switched to the 100-item Modified MMSE(28) after the first year, we converted the Modified MMSE back into a 30-point scale to allow the merger of data from the original and African-American cohorts. [TMI?] Baseline scores for SRHL [I usually call this EVGGFP, but I’m ok with SRHL], ADL, IADL, and upper-extremity function, as well as the presence or absence of difficulty walking ½ mile or up 10 steps, were included as covariates in each model. The same covariates were used in all regressions, so that any differences seen in the results for the different outcomes could be attributed to the outcomes themselves, rather than to differences in the covariates selected. Covariates with a non-normal distribution were normalized by log transformation.
The valid N for individual variables ranged from 5729 to 5868. Preliminary regressions using the chief predictor, kcal, plus all selected covariates yielded models with a valid N of 4,399 due to missing values. Eight covariates (income, bioresistance [a measure of lean body mass], low-density lipoprotein, pack-years of cigarettes smoked, calculated renal disease status, fibrinogen, and the Digit Symbol Substitution Test score) each had more than 80 missing values and were not significantly correlated with any outcome measure. [TMI?] Removing them increased the valid N to 5,392. The remaining variables, listed in Table 1, were included as covariates in the regressions reported below.
RESULTS
Table 1 shows the baseline characteristics of the study cohort. African Americans made up 16.4% of the sample. The participants were well-educated with an average of 1.7 years beyond secondary school; 74.4% reported good to excellent health. Among the 5858 participants with evaluable data on functional status, the prevalence of disability was substantially higher among women compared to men. Ten percent of women but only 5.6% of men reported dependence in ( 1 basic ADL. Among women, 30.7% reported dependence in ( 1 IADL, compared to 19.1% of men. More than twice as many women than men reported difficulty walking ½ mile or climbing up 10 steps (17.8% v 8.3%), as well as difficulty reaching, lifting, or gripping (17.8% v 8.3%). [These numbers are identical, which seems a bit coincidental. Was there an error in the tables?] [As I mentioned in my e-mail, I had fixed that but then apparently reverted to an earlier version – I work at chs only 1 day a week, so probably updated this on one of my other computers. Whine whine. Anyway, it works now. Or does it?] The amount of baseline leisure-time and chore-related physical activity ranged from a low of 0 kcal per week to over 13,000 kcal per week, regardless of age group. The mean weekly energy expenditure declined in the older age groups and was consistently lower in women than men (Table 2a). However, within a given quintile of physical activity, the mean and median energy consumed remained relatively stable with increasing age (Table 2).
Survival in the 11 years after baseline averaged 9.96 (( 2.34) [as I mentioned above, the 2.34 is a standard deviation. You should say so, perhaps right here, because a lot of people would present the standard error using this notation]. years for participants aged 65 to 69 and 8.09 (( 3.31) years for those aged 75 and older (Table 3). Over 11 years of follow-up, years with reported good to excellent health averaged 2.21 to 2.66 years less than mean survival, depending on age group. Over 6 years of follow-up, older participants on average had fewer disability-free years than younger participants. The study cohort had fewer mean years free of IADL disability than ADL disability, with the disparity widening slightly with age (0.71 years for those 65-69, 0.97 years for those 75+). On average, study participants experienced slightly fewer years free of mobility impairment than upper-extremity impairment, and this difference increased with age, from 0.13 year for those 65-69 to 0.46 year for the oldest age group.
The outcome measures were highly associated with exercise variables in the hypothesized direction. However, adjusting for the covariates decreased the apparent benefit of exercise by nearly a year, on average. In the following we present only the adjusted outcomes. [I think this is interesting and cautionary].
Higher baseline levels of physical activity among individuals aged 65-69 did not significantly improve either survival or years with reported good to excellent health over 11 years of follow-up, compared to those in the least active quintile (Figures 1a and 1b). A similar lack of impact was observed for the 70-74 age group, except for persons in the most active quintile. However, among participants aged 75 and older at study entry, additional years of life and healthy life [here you do refer to years of healthy life. I am happy.] increased monotonically with increasing levels of physical activity. After adjustment for covariates, the most active individuals at baseline lived an average of 1.02 years longer and experienced an average of 1.23 more years of self-reported healthy life than their inactive peers.
Greater physical activity enabled all 3 age groups to achieve longer independence in IADLs than those in the least-active quintile during 6 years of follow-up, after adjusting for covariates (Figure 2a). For the 65-69 group, the relationship between higher levels of physical activity and additional years of IADL independence was asymptotic, peaking at 0.42 ( 0.11 additional years. The 70-74 and > 74 age groups experienced linear increases in years free of IADL dependence as a function of increasing levels of physical activity, with gains of 0.72 ( 0.12 and 0.78 ( 0.13 years, respectively, for the most active seniors. Relative to the least active quintile, higher levels of physical activity yielded fewer additional years free of ADL dependence than IADL independence, after adjustment for covariates, and did not yield significant gains in either of the 2 highest activity levels in the 65-69 group (Figure 2b). The gains in ADL-free years, relative to the least active quintile, rose with increasing levels of physical activity among participants over age 69, but were highest in the oldest age group.
Figure 2c demonstrates a generally linear trend, for each age group, in the gain of years free of mobility impairment with higher activity quintiles, compared to the least active quintile. The relative gains in years of mobility independence, which were small and mostly statistically insignificant in those aged 65-69, became larger with each successive age group. The most active quintile in the 70-74 and ( 75 age groups respectively experienced 0.65 ( 0.14 and 1.01 ( 0.14 more years of mobility independence than the least active quintile of their respective age groups. In contrast to mobility independence, the benefits of physical activity for years free of upper-extremity dependence were essentially confined to the most active seniors in the oldest age group (Figure 2d).
DISCUSSION
Our study suggests that the survival advantage conferred byassociated with physical activity in persons over age 65 accrues primarily to persons of advanced old age (75+) who expend more than 1000 kcal per week in physical activity. The lack of association between physical activity and survival in the young-old may reflect, in part, their low overall mortality rate. While performing moderate to intense physical activity in advanced old age could be construed simply as a marker of robust health leading to greater survival, our adjustment for an extensive array of personal and health characteristics casts doubt on such an explanation. The threshold of approximately 1000 kcal/wk in physical activity for a statistically significant survival benefit is consistent with the results of Manini et al. (7), who assessed energy expenditure in high-functioning community-dwelling adults over age 69 and followed them for an average of 6.2 years. Active energy expenditure (AEE) between 521 and 770 kcal/day (measured by double-labeled water) was associated with a 35% lower mortality risk, compared to individuals with an AEE < 521 kcal/day. An AEE of 521-770 kcal/day corresponded to an average of 1204 kcal/wk derived from reported physical activity. By contrast, analysis of data from the Study of Osteoporotic Fractures (SOF) cohort study (7553 women, mean age 76.9) revealed a lower threshold of 163-503 kcal/week to achieve a significant reduction in mortality. SOF also did not find a clear dose-response effect on mortality risk reduction with increasing activity quintiles. The lower threshold activity may have been due, in part, to the use of different methodology to assess physical activity (4).
Although reported exercise behavior before age 65 was not associated with any study outcomes in our multivariatemultivariable models, we did not have information on exercise for the years immediately preceding enrollment for participants older than 65 at study entry. [This reminds me that we (or at least I) once discussed one more set of regressions where we remove all the variables that might conceivably be in the causal pathway --- just in case some readers think we over-controlled. Maybe that is just too complicated. I don’t recall if we decide *not* to do this.] Consequently, we were unable to determine whether the survival benefit of physical activity was driven by a long-term, cumulative effect on health or by a more near-term effect. In the Study of Osteoporotic Fractures, 7553 women underwent 2 assessments approximately 6 years apart and were followed for an additional 6.7 years. The investigators found that staying or becoming active produced was associated with similar reductions in the hazard rate ratios for all-cause and cardiovascular mortality, after adjusting for age, smoking, BMI, self-reported health, and a variety of comorbidities. Conversely, becoming sedentary was equivalent to remaining sedentary in conferring an increased risk of dying (4). The Gregg study, too, is prone to selection bias, in that persons who changed their level of exercise were likely to have done so because of their health. Although restricted to women, the results suggest that current, not past, physical activity in old age confers survival benefit, and that this survival benefit attenuates over the span of a few years once an individual becomes inactive. By contrast, our analysis, as well as results for women (but not men) from the Framingham Study, have shown that a single assessment of physical activity in persons aged 75 and older can predict a lower risk of mortality as far out as 10 to 11 years(10). A major confounder in interpreting epidemiological studies of exercise and mortality in the elderly is the lack of information on the variability of exercise behavior following activity assessment and the role of this variability in determining the longitudinal effects of exercise on mortality.
A striking finding of our study was the manner in which the effect of baseline physical activity on the number of years with reported good health closely paralleled the effect on actual survival. [I do think this is a striking finding, and have even written a paper about it – unpublished to date. However, most people will think that this is obvious, because YHL are limited by YOL – can’t be healthy and dead. Maybe remove this sentence? FYI, my manuscript is at if you care.]Poor self-rated health (SRH) has been shown to be a robust predictor of mortality in older persons, even after adjustment for comorbidities (29). In turn, physical activity has been shown to correlate significantly with SRH in middle-aged and older adults, as well as in persons with chronic illness and disability (30-32). Using logistic regression, Leinonen et al. observed that a decline in physical activity, but not baseline physical activity, predicted a decrease in SRH [a new name for this variable? I usually called in evggfp, but ok with me to do something different, just be consistent] over 5 years in a Finnish cohort of 75-year-old men and women (33). [there is probably self-selection bias in this paper too, right?] More research is required to explore the inter-relationships between physical activity and other known determinants of self-rated health.
Although muscle strength declines with age, it may remain above the threshold for an effect on physical performance among sedentary young-old adults. With advancing age, this threshold has a greater likelihood of being crossed (34), enabling the relative benefits of a physically active versus sedentary lifestyle on the development of disability to become manifest. We have previously shown in the CHS cohort that weekly physical activity expressed in kilocalories independently correlates with gait speed and the time to complete 5 chair stands (35), measures that are directly related to quadriceps strength (34, 36). As with survival, we could not determine in the present analysis whether the protective effect of baseline physical activity on disability-free years occurred as a result of cumulative physical activity throughout old age, or whether the effect was more proximal. Christensen et al. analyzed the impact of inactivity on mortality among 387 survivors of the Glastrup (Denmark) 1914 age cohort (13). After adjustment for gender, smoking, and household composition, physical inactivity at age 70 predicted disability at age 75, whereas cumulative physical activity between ages 50 and 70 did not.
Unlike its effect on years free of impaired mobility, physical activity did not significantly increase years free from upper-extremity impairment until after age 74, and only in the those in the 2 uppermost activity quintiles. [NEED RESULTS ON AGE-STRATIFIED PREVALENCE OF UE DYSFXN.] These observations could reflect better preservation of upper-extremity than lower-extremity function in advanced old age. The type of exercises, like weight lifting, that would benefit lifting, reaching, and grasping may not require a greater expenditure of energy per se, but might only occur as part of more overall intensive exercise regimens. The selection of activities in the CHS activity questionnaire could also bias against showing a benefit for upper-extremity function. Of the 17 activities, 7 emphasize lower-body exercise (eg, walking, hiking), 8 involve mixed upper- and lower-body activity (eg, swimming, gardening), and only 2 reflect mostly upper-body activity (bowling and raking).
Some studies are restricted to healthy people. A strength of our study is that it refers to persons in a general population (subject to their having enough baseline data). We also account for death when looking at the other non-survival outcomes, by looking at the number of years in which there are good outcomes.
Conclusions
In cross-sectional analysis, the mean leisure-time energy expenditure declines in successively older age groups, but when stratified by quintile of activity, the mean energy expenditures of seniors over age 74 are similar to those of seniors aged 65-69. [this weird statement is a function of my having given you tables using the non-age-specific quintiles. You’ll see that it’s no longer true.] A single measurement of physical activity predicts survival and years with self-reported good health up to 11 years later, as well as years free of disability up to 6 years later. After adjustment for demographic and health characteristics, the extra survival and years of healthy life within an age group conferred byassociated with leisure-time physical activity (compared to being sedentary) are proportionate to the amount of physical activity, are generally not statistically significant until after age 74, and are modest even at the highest weekly energy expenditures. Relative to sedentary older adults, seniors who are physically active also have more disability-free years for ADL, IADL, mobility, and upper-extremity function. With the exception of upper-extremity function, extra disability-free years can be observed before age 75 with less weekly energy expenditure than required to show a survival benefit. The absolute gain in disability-free years is small, even for the most active seniors.
This study has several important limitations. Although we controlled for an extensive array of health-related variables, physical activity may still be a marker for unmeasured good health. That is, it may not be exercise that makes older individuals healthier, but rather that being healthy allows older individuals to exercise. Because the CHS does not have accurate estimates of pre-baseline physical activity, we were unable to determine whether taking up exercise in old age confers the same benefit for survival and disability-free years as always being active.
ACKNOWLEDGEMENTS
The research reported in this article was supported by contracts N01-HC-35129, N01-HC-45133, N01-HC-75150, N01-HC-85079 through N01-HC-85086, N01 HC-15103, N01 HC-55222, and U01 HL080295 from the National Heart, Lung, and Blood Institute, with additional contribution from the National Institute of Neurological Disorders and Stroke. A full list of participating CHS investigators and institutions can be found at .
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[1] (Corresponding author) Depts. of Medicine and Public Health Sciences, Div. of General Medicine, University of California, Davis Medical Center, PSSB-2400, Sacramento, CA 95817. Ph: 916-734-7005; Fx: 916-734-2732. E-mail: chhirsch@ucdavis.edu
[2] (Alternate corresponding author) Dept. of BioStatistics, University of Washington, Seattle, WA 98195. Ph: 206-543-8004; Fx: 206-543-3286 E-mail: paula@pdiehr@u.washington.edu
[3]j€‚?Ž Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA
[4] Human Nutrition Research and Extension, US Dept. of Agriculture, Washington, DC
[5] Div. of Epidemiology and Clinical Applications, National Heart, Lung, and Blood Institute, Bethesda, MD
[6] Depts. of Medicine and Public Health Sciences, Univ. of Arizona, Tucson, AZ
[7] Div. for Heart Disease and Stroke Prevention, Centers for Disease Control and Prevention, Atlanta, GA
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