Timing of physical activity and risk of future cardiovascular disease

Physical activity is beneficial to health. Current guidelines emphasize sufficient moderate-to-vigorous physical activity (MVPA; ≥150 min per week), but do not provide specific guidance on exercise timing.1 Prior observations suggest that exercise timing may influence downstream effects. First, exercise is a powerful modulator of circadian rhythm,2 which has been linked to cardiometabolic disease. Second, many physical activity benefits are mediated by metabolic pathways influenced by circadian rhythm.2 Third, evidence suggests distinct metabolic responses to exercise at varying times of the day.3 Importantly, prior studies have been limited by reliance on self-reported physical activity, modest sample sizes, and a focus on composite outcomes, which may mask disparate associations. Here, among ∼90 000 UK Biobank participants who underwent prospective accelerometer-based physical activity measurement, we quantified the effects of guideline-adherent MVPA across validated categories of exercise timing (e.g. morning, afternoon, and evening), with respect to incidence of atrial fibrillation (AF), heart failure (HF), coronary artery disease (CAD), and cardiovascular mortality.