Is there an optimum amount of exercise to prevent heart disease?
Question Does age modify the associations between physical activity and all-cause mortality?
Across all age groups, a dose-response (the more, the better) of physical activity association with reduced all-cause mortality in >2 million individuals with 11-year follow-up
Discussion
In this cohort study with a pooled analysis of more than 2 million adults, we observed that age somewhat modifies the association between meeting the PA recommendations and all-cause mortality. This age-dependent association showed a distinct pattern compared with those observed for other modifiable health factors. Although the mortality risk reduction associated with meeting the PA recommendations either remained stable or slightly increased with age, the benefits related to other health factors diminished as age advanced.
Overall, previous evidence35-41 indicates that the impact of certain modifiable health factors on mortality risk diminishes with age, indicating that their relative importance is lower among older adults compared with younger individuals. This observation could be attributed to selection bias, suggesting that individuals who are biologically more vulnerable to the adverse effects of risk factors may die earlier, leaving a population of older adults who are inherently less susceptible (ie, survivors), thereby decreasing the apparent association between these risk factors and mortality with advancing age. Conversely, extensive research within prospective cohorts that include a large proportion of older adults has consistently highlighted PA as a crucial determinant for enhancing survival later in life.23,42 Furthermore, stratified analyses from these studies have revealed age-dependent associations between PA and mortality. For example, Arem et al23 pooled data from 6 Western cohorts (5 from the US and 1 from Sweden) as part of the National Cancer Institute Cohort Consortium, encompassing 661 137 men and women with a median age of 62 years (range, 21-98 years), and identified a significant interaction (P < .001) across 4 age groups (ie, <50, 50-59, 60-69, and ≥70 years). Similarly, Liu et al42 analyzed data from 467 729 adults across 9 Asian cohorts within the Asia Cohort Consortium, with a mean age of 55 years (range, 48-60 years), and observed that the association between PA and mortality was more pronounced among older participants (≥65 years) compared with younger ones (<55 years and 55-64 years) at baseline (P for interaction = .04).
Differences in the association between PA, as measured in MET-hours per week, and mortality risk became notably more pronounced between younger and older age groups, particularly beyond the 15 MET-hours per week threshold but taking into account that any amount of PA was better than none. Yet, on average, only 25% of adults participate in PA exceeding this level, with engagement in such activities sharply declining from the age of 60 years onward. Consequently, if a larger fraction of older adults were engaged in PA levels beyond 15 MET hours per week, a more substantial reduction in mortality risk could potentially be observed. Several factors contribute to why the mortality benefits of PA may be similar or even greater for older compared with younger adults. First, PA is more associated with certain causes of death,1,13 mainly those affecting the circulatory system,43,44, and heart disease remains the leading cause of death in the elderly.9-12 Second, aging is accompanied by a decline in task performance, mobility, fitness levels, coordination, and exercise economy, suggesting that older adults may reap substantial benefits from PA at lower levels of intensity owing to their reduced capacity for physical exertion.45,46 Third, ample evidence supports PA’s role in mitigating major aging hallmarks, such as genomic instability and mitochondrial dysfunction, thereby underscoring its preventative potential against the physiological processes of aging.47 Fourth, PA is instrumental in slowing the progression of functional impairments and frailty, which are critical factors associated with unhealthy aging and increased mortality risk, by counteracting the decline in physiological reserve and heightened vulnerability to stressors seen in old age. However, the greater association observed in older age groups might also reflect the capacity for doing PA (often considered a vital sign of health at advanced ages), with the somewhat increased association possibly attributable to more residual confounding by health status.33
Global and other PA guidelines do not differentiate recommendations by age; the advised amounts of PA for younger, middle-aged, and older adults are uniformly the same.13 Systematic reviews underpinning these recommendations have consistently demonstrated that meeting these PA levels is associated with a 20% to 30% reduction in mortality risk compared with individuals who do not meet these criteria. Our study introduces new insights, further affirming that the mortality benefits associated with PA not only persist across different age groups but may also slightly enhance with age. From a public health viewpoint, it is crucial to communicate to adults that engaging in an adequate amount of PA remains critically important throughout the lifespan, gaining even greater importance as one ages. Policy actions must be addressed to facilitate and promote desired amounts of PA that can promote PA engagement and sustainability at all stages of adult life. Our results also lend support for the current PA guidelines where adults of all ages are recommended the same amount of PA.
References:
https://health.gov/sites/default/files/2019-09/PAG_Advisory_Committee_Report.pdf
https://health.gov/sites/default/files/2019-09/PAG_Advisory_Committee_Report.pdf
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