Changes in Physical Activity and Cardiovascular Disease Risk in Cancer Survivors: A Nationwide Cohort Study.

Background: Cancer survivors face an elevated risk of cardiovascular disease, with physical inactivity after cancer treatment potentially worsening this risk. Objectives: The aim of this study was to investigate the association between physical activity before and after a cancer diagnosis and the risk for heart disease. Methods: A nationwide cohort of 269,943 cancer survivors (mean age 56.3, 45.7% men) was evaluated for physical activity adherence 2 years before and after diagnosis. The primary outcomes were the incidence of myocardial infarction (MI), heart failure (HF), and atrial fibrillation. Subdistribution HRs (sHRs) and 95% CIs were calculated using Gray's method, accounting for death as a competing risk. Results: Over a follow-up period of 1,111,329.28 person-years, compared with those who remained inactive, persistent physical activity was associated with a 20% reduction in MI risk (sHR: 0.80; 95% CI: 0.70-0.91) and a 16% reduction risk in HF risk (sHR: 0.84; 95% CI: 0.78-0.90). Initiating physical activity after a cancer diagnosis was linked to an 11% lower risk for MI (sHR: 0.89; 95% CI: 0.79-0.99) and a 13% lower risk for HF (sHR: 0.87; 95% CI: 0.82-0.93). Being active only before diagnosis was associated with a 20% lower risk for MI (sHR: 0.80; 95% CI: 0.71-0.91) and a 6% lower risk for HF (sHR: 0.94; 95% CI: 0.88-1.00). No association was observed between physical activity and atrial fibrillation risk. Associations varied by primary cancer site. Conclusions: These findings underscore the importance of maintaining physical activity for cardiovascular health in cancer survivors and suggest that physical activity before a diagnosis may offer enduring protection against ischemic heart disease and cardiac dysfunction.