One of the more interesting findings in the epidemiology of exercise, enabled by the development of lightweight accelerometers to measure daily activity, is that even very modest levels of movement and exertion have a significant correlation with health outcomes in later life. People who cook, walk a little, and tinker in the garden have meaningfully lower mortality rates than those who do not, and the effect scales through different degrees of this sort of low-level exercise. The important question to ask here is whether or not physical activity causes health benefits. The alternative explanation is that people who are healthier and more robust naturally tend to be more active. Human data usually doesn't allow for any inspection of causation, as opposed to the discovery of correlations, but animal studies have definitively shown that exercise causes improved health - although it doesn't appear to extend overall life span to any meaningful degree.
Despite impressive declines in age-standardized coronary heart disease (CHD) mortality rates since the 1960s, cardiovascular disease (CVD) remains the leading cause of death in the United States and globally. More than half a million older American individuals die of CVD annually. Physical activity (PA) is a key candidate for reducing CHD risk in older women. The long-standing, prevailing paradigm in PA research is that moderate to vigorous PA (MVPA) for at least 150 minutes per week is needed to prevent CVD in adults. However, a meta-analysis of 9 epidemiologic studies found reduced risks of CHD associated with levels of self-reported MVPA (≥3 metabolic equivalent tasks [METs]) that were lower than the recommended guidelines.
Light PA at intensity levels of 1.5 to 3.0 METs is poorly measured by self-reported questionnaires because they fail to capture light movements performed habitually throughout the day. Recent reports reveal that light PA measured by accelerometry is associated with reduced risks of total and CVD mortality, as well as favorable levels of CVD risk factors. In this prospective cohort study of older women, light PA measured by accelerometry was associated with a dose-responsive, independent reduced risk of incident CHD and CVD events. The highest quartile of light PA was associated with a 42% reduced risk of myocardial infarction or coronary death and a 22% reduced risk of incident CVD events compared with the lowest quartile of light PA. These reduced risks persisted after multivariable adjustment that included physical functioning and other measures of health status, even though some covariates may themselves be altered by PA and thus dilute the associations.