Stephen J.LurieMD, PhD, Senior EditorIndividualAuthorJody W.ZylkeMD, Contributing EditorIndividualAuthor
To the Editor: Dr Lee and colleagues1 suggested that even low-level exercise appears protective against CHD. Unfortunately, association studies cannot clarify whether the exercise causes these improved outcomes. As the authors point out, although the intensity of activity was much less than the reported activity in most earlier studies, the group differences observed were substantial and significant. The results of Lee et al also show no trend to improved outcomes for progressively more vigorous activity; although there was a significant but small trend toward benefit from increased energy expenditure, the group that expended 600 to 1499 kcal/wk actually had better outcomes than the group that expended 1500 kcal/wk and greater (Table 2). People older than 65 years who participated in social and productive activities, usually involving minimal physical activity, have been found to have significantly lower mortality over 13 years than nonparticipators,2 and the magnitude of mortality reduction was quite similar to the reductions of CHD noted by Lee et al. This near absence of dose-benefit relationship weakens the cause-effect hypothesis.
Lesser GT. Intensity of Physical Activity and Risk of Coronary Heart Disease. JAMA. 2001;285(23):2973-2974. doi:10.1001/jama.285.23.2973