Physical activity and risk of thyroid cancer: a systematic review and meta-analysis of prospective cohort studies.

[BACKGROUND] The preventive effect of physical activity on the risk of thyroid cancer remains inconsistent and unclear. We investigated the association between physical activity and the risk of thyroid cancer using a meta-analysis of prospective cohort studies.

[METHODS] A systematic search of PubMed and EMBASE was conducted from inception till December 20, 2024. A pooled relative risk (RR) with its 95% confidence interval (CI) was calculated using an adjusted RR with its 95% CI from each study.

[RESULTS] A total of nine prospective cohort studies (N = 2 764 014 adults; incident thyroid cancer cases, 15 166) were included in the final analysis. In the meta-analysis of all the studies, highest physical activity was not significantly associated with the risk of thyroid cancer (RR, 0.91; 95% CI 0.76-1.09; I = 56.5%), compared with lowest physical activity. Physical activity was statistically significantly associated with a decreased risk of thyroid cancer in the studies conducted in Asia (RR, 0.75; 95% CI 0.64-0.88; I = 4.2%), but not in either Europe or North America. Also, physical activity was statistically significantly associated with a decreased risk of thyroid cancer in the studies published after 2015 (RR, 0.78; 95% CI 0.65-0.93; I = 22.1) and the high-quality studies (RR, 0.81; 95% CI 0.70-0.94; I = 5.2).

[CONCLUSIONS] Physical activity decreased the risk of thyroid cancer in the studies conducted in Asia, published after 2015, and rated as having high methodological quality. Further high-quality prospective cohort studies are warranted to confirm our findings.