Impact of Health Behaviors on Cardiovascular Risk in Thyroid Cancer Survivors according to Metastasis: A Nationwide Cohort Study

Background: Patients with thyroid cancer receive thyroid-stimulating hormone suppressive therapy and radioactive iodine therapy, which can alter metabolism and affect the association between lifestyle factors and cardiovascular disease (CVD) outcomes. However, it remains unclear how changes in lifestyle relate to CVD risk, particularly according to metastatic status. We investigated the impact of baseline and changing lifestyle behaviors on CVD risk among thyroid cancer patients by metastasis status. Methods: This study was a nationwide cohort study using data from the Korean National Health Insurance Service claims database with the Cancer Clinical Library Database from the Korea Clinical Data Utilization Network for Research Excellence project. Over a mean follow-up of 5.7 years, 99,742 thyroid cancer patients were analyzed. Results: Current smoking increased CVD risk in both no metastasis (NM) group (hazard ratio [HR], 1.77; 95% confidence interval [CI], 1.33 to 2.35) and the local metastasis (LM) group (HR, 1.30; 95% CI, 1.00 to 1.68), but not in those with distant metastasis. Regular activity reduced the risk in the NM group (HR, 0.84; 95% CI, 0.79 to 0.96). Alcohol consumption was not significantly associated with the CVD risk. Sustained smoking showed an increased CVD risk in both NM (HR, 1.95; 95% CI, 1.31 to 2.90) and LM (HR, 1.88; 95% CI, 1.28 to 2.77). Sustained regular physical activity was associated with a lower risk of CVD only in NM (HR, 0.68; 95% CI, 0.53 to 0.87). Conclusion: Sustained smoking increased CVD risk, while regular physical activity was associated with a lower risk of CVD, particularly in those without distant metastasis.