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Address correspondence to: Ian Janssen, PhD, School of Kinesiology and Health Studies, Queen's University, 28 Division St., Kingston, Ontario, Canada, K7L 3N6
School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, CanadaDepartment of Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada
Division of Preventive Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MassachusettsDepartment of Epidemiology, Harvard School of Public Health, Boston, Massachusetts
Department of Exercise Science and the Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina
Physical inactivity is an important modifiable risk factor for noncommunicable disease. The degree to which physical activity affects the life expectancy of Americans is unknown.
Purpose
This study estimated the potential years of life gained due to leisure-time physical activity in the U.S.
Methods
Data from the National Health and Nutrition Examination Survey (2007–2010); National Health Interview Study mortality linkage (1990–2006); and U.S. Life Tables (2006) were used to estimate and compare life expectancy at each age of adult life for inactive (no moderate to vigorous physical activity); somewhat-active (some moderate to vigorous activity but <500 MET minutes/week); and active (≥500 MET minutes/week of moderate to vigorous activity) adults. Analyses were conducted in 2012.
Results
Somewhat-active and active non-Hispanic white men had a life expectancy at age 20 years that was ∼2.4 years longer than that for the inactive men; this life expectancy advantage was 1.2 years at age 80 years. Similar observations were made in non-Hispanic white women, with a higher life expectancy within the active category of 3.0 years at age 20 years and 1.6 years at age 80 years. In non-Hispanic black women, as many as 5.5 potential years of life were gained due to physical activity. Significant increases in longevity were also observed within somewhat-active and active non-Hispanic black men; however, among Hispanics the years-of-life-gained estimates were not significantly different from 0 years gained.
Conclusions
Leisure-time physical activity is associated with increases in longevity.
Introduction
Concern about the deleterious health effects of a physically inactive lifestyle is at an unprecedented level. Less than half of the adult population meet physical activity guidelines of 150 minutes per week of moderate to vigorous physical activity (MVPA).
The benefits of physical activity usually are expressed by comparing the relative risks of disease and mortality in physically active and inactive groups.
Although these statistical estimates are informative to researchers and practitioners, the general public may not understand or be captivated by them. Another way to express the benefits is to compare the life expectancy of physically active and inactive people. Health messages that focus on life expectancy are easy to understand, and they may motivate inactive people to adopt an active lifestyle.
The five studies addressing this question suggest that physical activity increases life expectancy by 1.3 to 5.5 years. Although they are informative, these studies have important limitations. None were based on representative data sets, four
considered whether the effects vary by age, and none considered racial/ethnic variations. As the effects of physical activity may vary according to these demographic characteristics, and because it is important to have tailored health messages,
age-, gender-, and race/ethnicity-specific data are needed.
Therefore, the primary objective of the present study was to estimate the years of life gained due to leisure-time physical activity for the U.S. adult population. Estimates were provided across the adult life span, for both genders, and in various racial/ethnic groups. A secondary objective was to estimate the hours of life gained at entry into adulthood (age 20 years) per hour of leisure-time physical activity participated in during adulthood.
Methods
Overview of Calculation Method
The years of life gained due to leisure-time physical activity were estimated using the following information: (1) the proportion of varying levels of leisure-time physical activity in each year of adult life obtained from the 2007–2010 National Health and Nutrition Examination Survey (NHANES); (2) the hazard ratio for death associated with varying levels of leisure-time physical activity obtained from the 1990, 1991, and 1995 National Health Interview Survey (NIHS), with mortality follow-up to 2006; and (3) the probability of death during each year of life obtained from the 2006 U.S. life tables. All analyses were conducted in 2012.
Proportion Within Physical Activity Categories
The proportion of the population within three physical activity categories were obtained from the 2007–2010 NHANES, a representative sample of the non-institutionalized U.S. population.
Hispanics, non-Hispanic blacks, and older adults were oversampled, and sample weights were used to produce unbiased estimates. Herein, only non-Hispanic white, non-Hispanic black, and Hispanics were examined; the sample sizes of other racial/ethnic groups were insufficient.
The NHANES physical activity questionnaire asked participants to report the number of days in a typical week and the average duration per day they participated in the following activities for ≥10 consecutive minutes: (1) walking or bicycling for transportation; (2) moderate-intensity sports, fitness, or recreational activities (activities that result in moderate increases in heart rate and breathing); and (3) vigorous-intensity sports, fitness, or recreational activities (activities that result in large increases in heart rate and breathing). Assuming a MET of 4.0 for walking/bicycling, 4.0 for moderate-intensity, and 8.0 for vigorous-intensity activities,
these data were used to estimate the MET minutes/week of MVPA that fell outside of routine activities of daily living and work. Participants were placed into inactive (0 MET minutes/week); somewhat-active (some activity but <500 MET minutes/week); or active (≥500 MET minutes/week) leisure-time physical activity categories.
A total of 500 MET minutes/week of MVPA is equivalent to the public health guidelines for physical activity (e.g., 150 minutes of moderate activity or 75 minutes of vigorous activity or an equivalent combination of the two intensities).
For each gender and racial/ethnic group, and specific to each age, the current study estimated the proportion of individuals who were physically inactive, somewhat active, and physically active. Because of the small number of participants within each 1-year age group, within each gender- and race/ethnicity-specific group, an estimate was made of the probability of being in each physical activity category using separate logistic regression models run on cubic polynomial age terms (age, age2, age3).
Thus, the proportion of participants within each activity category across age was calculated using a smoothing procedure based on moving averages. All logistic models were fit using SAS, version 9.2.
Hazard Ratio for Death Within Physical Activity Categories
To estimate the hazard ratio for death, the data used were from the 1990, 1991, and 1995 NHIS and its linked mortality files. The NHIS is an annual nationally representative cross-sectional survey.
The 1990, 1991, and 1995 cycles were the only pre-2000 cycles that included a questionnaire that could assess adherence to physical activity guidelines. The NHIS mortality files combine the survey data with mortality data from the National Death Index through December 31, 2006. The final-analysis sample consisted of 95,358 adults (aged ≥18 years), of whom 18,568 died, with a total of 912,781 person-years of follow-up. Analyses took into account the sample weights and complex survey design.
The NHIS physical activity questionnaire asked participants to report the frequency with which they participated in 20 common leisure-time physical activities (and two other activities not on that list) over the past 2 weeks, the average duration of activity on each occasion, and the intensity of these activities (moderate: moderate increase in heart rate and breathing; or vigorous: large increase in heart rate and breathing). As explained above for NHANES, the average MET minutes/week of MVPA was calculated for each participant, and they were placed into the same inactive, somewhat-active, and active categories. Age, smoking status (never, former, current), annual household income (<$10,000; $10,000–$19,999; $20,000–$34,999; $35,000–$49,999; ≥$50,000; did not report); and occupational activity were included as confounders in the hazard ratio estimates.
An a priori decision was made to force all of these confounders into the regression models, as they are known correlates of leisure-time physical activity and mortality. For occupational activity, if employed, participants were assigned a MET for their occupation type.
If their major activity was keeping house, participants were assigned an occupational MET of 2.43, the average of nine housework and food preparation activities.
If their major activity was going to school, participants were assigned an occupational MET of 1.91, the average of 13 taking classes and homework activities.
The hazard ratios were generated using Cox proportional hazard models in SAS, version 9.2. Variables in the models were physical activity, age, age2, smoking, income, and occupational MET. Interaction terms between age and physical activity were considered, but because these were not significant, they were not retained. The Schoenfeld residuals indicated that there were no violations of the proportional hazards assumption.
Probability of Death at Each Age and Years-of-Life-Gained Estimate
The 2006 U.S. life tables were used to derive information on the probability of death during each year of life starting at age 18 years.
For each 1-year age interval within each gender and race/ethnicity group, an estimate was obtained of the probability of death conditional on having lived to the start of that interval. The approach and calculations used to estimate the years of life gained due to leisure-time physical activity is based on the methods developed by Fontaine and colleagues
who provide more details on this approach and the specific formulas used for the calculations.
In the current study, the following calculations were performed within each gender and race/ethnicity group. First, the probability of death in each 1-year age group from the U.S. life tables,
which is unconditional on leisure-time physical activity, was multiplied by an age- and physical activity category–specific adjustment factor. This adjustment factor equaled the hazard ratio for the physical activity category of interest, divided by the sum of the product of the proportion of people in each physical activity category and their respective hazard ratio for mortality. Second, using the adjusted probability of death estimates, the median life expectancy within each physical activity category at each age was estimated. Third, for each age, the years of life gained due to leisure-time physical activity were calculated as the difference between the life expectancy of a person in the inactive category and that for similar people in the somewhat-active and active categories.
Estimate of Hours of Life Gained per Hour of Leisure-Time Physical Activity
The hours of life gained per hour of leisure-time physical activity participated in also were estimated. These estimates were based on the years-of-life-gained estimates for the active category, the remaining life expectancy at age 20 years within the active category, and the amount of leisure-time required to achieve the physical activity guideline every week over the remaining life expectancy (150 minutes/week of moderate or 75 minutes/week of vigorous activity
). Because life expectancy gains at midlife and old age reflect both past and future physical activity, the hours-of-life-gained estimates were calculated only for age 20 years.
Results
Irrespective of gender and race/ethnicity, there was a noticeable difference in the proportion of NHIS and NHANES participants in the active category (Table 1). The hazard ratio estimates for mortality for the three physical categories are in Table 2. Within non-Hispanic white and non-Hispanics, the somewhat-active and active categories had a reduced mortality risk, with hazard ratio values in the range of 0.74 to 0.83 for the somewhat-active category and 0.58 to 0.82 for the active category. Leisure-time physical activity was not associated with a lower mortality risk in Hispanics.
Table 2Mortality risks across the leisure-time physical activity categories within the NHIS
Population subgroup
Unweighted sample Size
Person-years of follow-up
Number of deaths
Physical activity category
Inactive
Somewhat-active
Active
Non-Hispanic white men
31,975
434,290
6575
1.00
0.80 (0.74, 0.87)
0.80 (0.74, 0.85)
Non-Hispanic black men
4,547
59,976
1113
1.00
0.74 (0.59, 0.94)
0.82 (0.67, 0.99)
Hispanic men
3,449
47,292
385
1.00
1.13 (0.79, 1.61)
0.88 (0.65, 1.21)
Non-Hispanic white women
42,195
578,876
8582
1.00
0.83 (0.77, 0.90)
0.75 (0.70, 0.81)
Non-Hispanic black women
8,321
115,513
1483
1.00
0.76 (0.61, 0.94)
0.58 (0.45, 0.75)
Hispanic women
4,871
67,735
430
1.00
1.04 (0.74, 1.47)
1.01 (0.70, 1.46)
Note: Data in the last three columns are presented as hazard are presented as hazard ratio (95% CI) and were adjusted for age, age2, smoking, income, and occupational activity.
Figure 1 illustrates the potential years of life gained for the active category across the adult life span. There were noticeable differences across age, race/ethnicity, and gender. Table 3 presents the years of life gained for the somewhat-active and active categories at ages 20, 30, 40, 50, 60, 70, and 80 years. Somewhat-active and active non-Hispanic white men had an estimated life expectancy at age 20 years that was ∼2.4 years longer than that of the inactive men; this life expectancy advantage decreased to 1.2 years by age 80 years. Similar observations were made in non-Hispanic white women, with a higher life expectancy within the active category of 3.0 years (95% CI=2.2, 3.8) at age 20 years, and 1.6 years (95% CI=1.2, 1.9) at age 80 years.
Figure 1Potential years of life gained in the active category across the adult lifespan
The patterns were even more striking in non-Hispanic black women, with as many as 5.5 (95% CI=3.0, 8.0) years of life gained due to physical activity. Significant increases in longevity also were observed within somewhat-active and active non-Hispanic black men; however, among Hispanic men and non-Hispanic women the years-of-life-gained estimates were more variable, and regardless of age, were not significantly different from 0 years gained. Irrespective of age, gender, and race/ethnicity, the years-of-life-gained estimates in the active and somewhat-active groups were similar, and the overlapping 95% CIs indicate that they were not significantly different from each other (Table 3).
The hours of life gained per hour of leisure-time physical activity accumulated during the adult life span were estimated for age 20 years (Table 4). Men aged 20 years were estimated to gain as much as 2.6 hours of life per hour of moderate activity and as much as 5.4 hours of life per hour of vigorous activity. Women aged 20 years were estimated to gain as much as 5.6 hours of life per hour of moderate activity and as much as 11.3 hours of life per hour of vigorous activity.
Table 4Hours of life gained in the active category per hour of moderate and vigorous physical activity
Additional analyses were performed to consider whether using more-conservative MET values to calculate leisure-time physical activity energy expenditure influenced the results (i.e., 3.0 METs for walking/bicycling and moderate activity, 6.0 METs for vigorous activity). This change had a minimal effect on the relationships between leisure-time physical activity and mortality, and the years-of-life-gained estimates did not fall outside of the 95% CIs shown in Table 3. Additional analyses were performed to consider whether the estimates of years of life gained were affected by differences in the proportions of NHIS and NHANES participants in the three activity categories. The maximal effect on this difference on the years-of-life-gained estimates was 0.1 years.
Discussion
Leisure-time physical activity has a meaningful association with life expectancy, at least within the non-Hispanic population, with as much as 5.5 years gained at age 20 years for non-Hispanic black women. The time in life gained due to leisure-time physical activity greatly exceeds the time it takes to accumulate this activity over the adult life span, particularly if the activity is performed at a vigorous intensity. For instance, a non-Hispanic white woman aged 20 years is estimated to gain 3.2 hours of life for each hour of moderate physical activity and 6.4 hours of life for each hour of vigorous physical activity engaged in during adulthood.
The years-of-life-gained estimates for the active category are congruent with the range of 1.3–5.5 years reported in previous studies.
The present study extends these observations by presenting nationally representative estimates and by presenting variations by gender, age, and race/ethnicity, which were quite meaningful. The current study also examined the hours of life gained, at entry into adulthood, for each future hour of leisure-time physical activity participation.
Although the point was not addressed in their original study,
noted, in response to several letters written about their paper, that for male Harvard alumni aged 40–70 years, 2.0–2.5 hours of life were gained per hour of future exercise accumulated to age 80 years. The estimates in the present study for non-Hispanic white men aged 20 years (the population group that most closely approximates Harvard alumni) suggest that 2.6 hours are gained per hour of moderate activity and 5.2 hours were gained per hour of vigorous activity accrued in adulthood. A key benefit of vigorous activity in comparison to moderate activity is that an individual needs to be active for only half as long to expend an appropriate amount of energy (e.g., 500 MET minutes/week). Discrepancies in the life expectancy estimates across studies are likely due to differences in study populations, physical activity questionnaires, and the cut-points used to define the activity groups.
The years-of-life-gained estimates for leisure-time physical activity compare favorably to estimates for obesity and other behavioral risk factors. At age 30 years, the active non-Hispanic men and women in the present study gained 2.0–5.4 years. Fontaine and colleagues
estimated that, at age 30 years, moderately obese (BMI= 33) whites lose 2 years of life, whereas moderately obese blacks do not lose any years. Other findings suggest that at age 30 years, vegetarian men and women have a 1.5-year longer life expectancy than nonvegetarians.
has examined the relationship between physical activity and mortality within Hispanics. In that study of Puerto Rican men, mortality risk was reduced with increasing physical activity such that the most-active quartile had a 45% reduction in risk. The current authors can only speculate as to why there was no association between leisure-time physical activity and mortality within the Hispanics in the current study.
It is possible that physical activity does not benefit Hispanics to the same extent as it does other ethnicities, although this is not supported by studies examining the effect of physical activity on other health outcomes.
Perhaps most of the physical activity of Hispanics is occupational in nature, and therefore not captured by the current study, which focused on leisure-time activity. However, including occupational activity as a covariate had only a slight effect on the relationship between leisure-time physical activities and mortality risk, and occupational activity was not an independent predictor of mortality in Hispanics (data not shown). The Hispanic category includes a mixture of ethnic groups, each of which varies considerably. Finally, because the types of leisure-time physical activity assessed in NHIS reflect conventional American behaviors, the activity of Hispanics may have been under-reported because it was not assessed in a culturally sensitive manner.
The present study was not void of limitations. First, the calculations assumed that people's leisure-time physical activity is constant over time. Second, the leisure-time physical activity measures were self-reported, and such reports are prone to social-desirability and recall biases.
Assuming that these biases are nondifferential, the hazard ratios for mortality and the estimates for years of life gained in the active groups would have been underestimated.
Third, the leisure-time physical activity questionnaires used in NHIS and NHANES changed over time. Therefore, there were comparability issues for the physical activity measures in these two surveys that may have had a subtle impact (≤0.1 years) on the years-of-life-gained estimates. Fourth, the relatively small sample size of non-Hispanic blacks and Hispanics resulted in imprecise estimates within these groups. Finally, dietary intake, obesity, and alcohol were not controlled for, as data on these variables were not collected in all NHIS cycles.
Conclusion
It is hoped that the findings of the current study can be used by clinicians and the public health community to develop effective messages on the importance of physical activity. Simple messages on changes in life expectancy are more easily understood than relative risk estimates and might influence physical activity behaviors.
the longevity estimates were presented as the years of life gained due to activity rather than the years of life lost due to inactivity. Finally, because it is important to tailor messages to the individual,
the gender-, age-, and race/ethnicity-specific estimates should be used when developing messages for individual patients and clients.
The current study shows that leisure-time physical activity has a meaningful association with longevity. Although adhering to a physically active lifestyle over the life span is a substantial time investment, this is a sound investment that is likely more than compensated for by the years of life gained. In fact, non-Hispanics can expect to gain 2.3–5.6 hours of life for every hour of moderate physical activity, and 5.2–11.3 hours of life for every hour of vigorous physical activity they accumulate during adulthood.
IJ and VC had full access to the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Funding for this project was provided by the Heart and Stroke Foundation of Ontario. IJ was supported by a Canada Research Chair. VC was supported by a CIHR Frederick Banting and Charles Best Doctoral Award. PTK is supported, in part, by the Louisiana Public Facilities Authority Endowed Chair. IML is supported, in part, by a grant from the NIH (CA154647).
IJ has received honoraria, speaker fees, and consulting fees from several nonprofit and government organizations that have an interest in physical activity and health. SNB serves on the scientific advisory boards of Technogym, Alere, Jenny Craig, Clarity, and Santech. He also receives honoraria and speaker fees from numerous government and commercial organizations. In the past 5 years, he has received research funding from the NIH, Department of Defense, Coca Cola, and Body Media. IML has served on the scientific advisory board of Virgin HealthMiles. She has received honoraria from several nonprofit and government organizations. In the past 5 years, she has received research funding from the NIH and Dow Corning.
No other authors reported financial disclosures.
References
Office of Surveillance Epidemiology and Laboratory Services of the Centers for Disese Control and Prevention
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