Abstract and Introduction
Abstract
Objective To study the association of self-reported physical activity level with prognosis in a cohort of patients with coronary heart disease (CHD), with a special focus on the dose–response relationship with different levels of physical activity.
Methods Data were drawn from a prospective cohort of 1038 subjects with stable CHD in which frequency of strenuous leisure time physical activity was assessed repeatedly over 10 years of follow-up. Multiple Cox proportional hazards regression models were used to assess the association of physical activity level with different outcomes of prognosis (major cardiovascular events, cardiovascular mortality, all-cause mortality), with different sets of adjustments for potential confounders and taking into account time-dependence of frequency of physical activity.
Results A decline in engagement in physical activity over follow-up was observed. For all outcomes, the highest hazards were consistently found in the least active patient group, with a roughly twofold risk for major cardiovascular events and a roughly fourfold risk for both cardiovascular and all-cause mortality in comparison to the reference group of moderately frequent active patients. Furthermore, when taking time-dependence of physical activity into account, our data indicated reverse J-shaped associations of physical activity level with cardiovascular mortality, with the most frequently active patients also having increased hazards (2.36, 95% CI 1.05 to 5.34).
Conclusions This study substantiated previous findings on the increased risks for adverse outcomes in physically inactive CHD patients. In addition, we also found evidence of increased cardiovascular mortality in patients with daily strenuous physical activity, which warrants further investigation.
Introduction
Extensive research has established that physical activity is inversely associated with the risk of developing cardiovascular disease in healthy adults. In patients with manifest cardiovascular disease, current clinical practice guidelines recommend encouraging patients to undertake daily moderate intensity physical exercise for secondary prevention. For example, a pertinent US guideline recommends 30–60 min moderate intensity aerobic activity, such as brisk walking, at least 5 days and preferably 7 days per week.
While such recommendations are based on numerous clinical trials clearly showing that exercise-based cardiac rehabilitation improves prognosis in heart disease patients, only a few prospective studies have examined the potential benefit of physical activity in clinical practice under real-life conditions. These consistently found the highest risks for adverse outcomes in the most inactive patients, yet the exact dose–response relationship with different levels of physical activity is still unclear. For example, one study found linear trends towards lower mortality with increasing levels of exercise; another study found a curvilinear association, with the greatest relative mortality differences in those with lower physical activity level and a levelling off of the risk with increasing levels; and another study even showed increased mortality rates in the vigorously active group.
In some disagreement with the tenor of recommendations outlined in clinical practice guidelines, these studies consistently reported substantial benefits of physical activity already at lower levels compared to inactive subjects, but with higher levels not conferring much (if any) additional benefit. Of note, most studies measure or consider physical activity at baseline only, which may lead to an underestimation of the risk in the lowest activity group since physical activity level is likely to decrease with age and thus over time.
In this study, we investigated the association of leisure time physical activity level with prognosis in a cohort of patients with coronary heart disease (CHD). We were especially interested in the dose–response relationship with different levels of physical activity and also took changes in physical activity level during long-term follow-up into account.