In a recent study published in the journal JAMA Network Open, researchers investigated the independent associations between sedentary behaviors and light-intensity physical activity (LPA) with healthy aging. Previous studies have shown that replacing sedentary behaviors with improved sleep quality or moderate-to-vigorous physical activity (MVPA) may improve individuals' odds of healthy aging (reaching the age of 70 years while being devoid of chronic ailments, mental health conditions, loss of physical function, or subjective memory impairment). However, the effects of LPA on healthy aging have never been systematically evaluated.
Study: Sedentary Behaviors, Light-Intensity Physical Activity, and Healthy Aging. Image Credit: Studio Romantic / Shutterstock
Using a sizeable female cohort (N = 45,176) with substantial follow-up (over 20 years), the current study highlights that while every two hours of daily television watching (sedentary behavior) resulted in a 12% reduction in odds of healthy aging, replacing this behavior with two hours of LPA increased these odds by 6% across all four domains of healthy aging. Notably, in individuals receiving less than seven hours of sleep daily, replacing even one hour of television time with sleep or MVPA achieved similar improvements in the probability of a long and healthy old age.
Live long AND prosper – is global aging a boon or a cause for concern?
Extending human lifespan remains one of the highlights of modern medicine – advances in medical research and public accessibility have increased the average global lifespan from 45 years in 1850 to almost 80 years today. In the past 60 years alone, reports estimate that medical improvements have resulted in an unprecedented 23-year increase in global life expectancy. While these figures are commendable and noteworthy, they have unexpectedly given rise to a novel concern – more than 8.5% of the world's population is aged 65 years or older, with this percentage expected to rise to 20% by 2050.
Unfortunately, evolutionary processes, particularly natural selection, progress at much longer timescales, resulting in old age (beyond the age of reproductive output) being oftentimes associated with adverse health effects, including chronic diseases, mental health disorders, cognitive decline, and physical impairments. Research estimates that only 10-35% of adults above 69 achieve 'healthy aging,' the ideal state of individuals' being devoid of age-related health concerns. Identifying approaches to achieve this ideal state is thus the need of the hour, with modifiable health behaviors (sleep duration and quality, physical activity, and sedentary behaviors) comprising the primary targets of ongoing research.
"Twenty-four–hour behaviors can be divided into sleep behavior, sedentary behavior (SB), light-intensity physical activity (LPA), and moderate- to vigorous-intensity physical activity (MVPA), which are important modifiable factors for health. Among them, MVPA has been associated with increased odds of healthy aging and sleep duration has been shown to have an inverted U-shaped association with healthy aging, with 7 hours daily sleep associated with the highest odds of healthy aging."
Isotemporal modeling MVPA has been shown to improve age-related health outcomes; sedentary behaviors are observed to have the opposite effect. Unfortunately, on average, MVPA comprises only 4% of adults' waking time in modern society, while sedentary behaviors comprise 60% or more. The transition from sedentary behaviors to LPAs is easier to achieve than a direct switch from the latter to MVPAs, particularly in elderly individuals. Unfortunately, the benefits of LPA in healthy aging have hitherto remained untested.
About the study
In the present long-term cohort study, researchers aim to evaluate the independent associations of LPA and sedentary behaviors with healthy aging to elucidate the benefits of replacing the latter with LPA, sleep, or MVPA in aging populations. The study adheres to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines. The study cohort was derived from the Nurses' Health Study (NHS) and included participants above 50 years without a prior medical history of major chronic diseases at baseline (1992). The follow-up period was 20 years, and the final assessment was conducted from January to March 2022.
The primary outcome of interest was survival to age 70 without the development of health-associated concerns, particularly across four health domains – chronic diseases, cognitive impairment, loss of physical function, or mental health disability.
"We included 3 SBs, 2 LPAs, MVPA, and sleep duration. Of these, we considered time spent sitting watching television as our primary exposure, because among the various surrogates for SB, time spent television watching is most strongly associated with adverse health outcomes."
Data collection was comprised of medical, anthropometric, and sociodemographic records from the NHS database. Pre-validated health questionnaires were employed to record the duration and intensity of participants' physical activity, sleep, and sedentary behaviors (collectively, 'exposures'). The isotemporal substitution model was used to compare measured exposures and their subsequent outcomes, with models corrected for age, ethnicity, education, marital status, family medical conditions, and known health risk factors (e.g., smoking).
Study findings and conclusions
After verifying study inclusion requirements, 45,176 participants were included in the analyses (mean age = 59.2 years), of which 3,873 (8.6%) participants achieved healthy aging. Study findings reveal that sedentary behaviors, particularly time spent watching television while seated, significantly worsened the odds of healthy aging by an average of 12% for every additional two hours spent in the activity. In contrast, LPA was associated with increased odds of healthy aging by a factor of 6% for every two hours of the behavior.
"Participants with longer television watching time were older, less educated, more likely to smoke or drink alcohol, more likely to have hypertension and high cholesterol, and more likely to have higher BMI and calorie intake and lower diet quality, compared with those who spent less time watching television"
Replacing television watching with any physical activity was observed to reverse the negative trend of the former on healthy aging, with the degree of benefit observed dependent on the intensity of physical activity pursued. Notably, replacing television watching with sleep produced similar benefits for individuals presenting less than seven hours of daily sleep.
These findings complement previous research calling for increased population-wide physical activity and reduced sedentary behaviors (prolonged television watching was observed to be the worst). Given that LPAs are more accessible to achieve than MVPAs for individuals (particularly those above the age of 50) unfamiliar with physical activity, this study may form the basis for future interventions targeting optimal health at older ages.
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