Lifetime Swimming Pool Attendance and Cancer Risk: Findings from the Multicase-Control Study in Spain (MCC-Spain).

Swimming in pools involves inhalation and skin absorption of potential carcinogenic disinfection byproducts (DBPs) as well as physical activity, which is protective for some cancer sites. We evaluated the association between lifetime pool attendance and the risk of breast, colorectal, and prostate cancer in a multicase-control study that recruited 4,941 hospital-based cancer cases (1,724 breast, 2,111 colorectal, 1,106 prostate) and 4,039 population-based controls in Spain (2008-2013). Lifetime swimming pool attendance in summer (as a surrogate of outdoor pools) and the rest of the year (as a surrogate of indoor pools), socio-demographics, and lifestyle were ascertained in face-to-face interviews. Cancer risk associated with pool attendance markers was estimated using linear mixed-effect models, adjusting for covariates with recruitment area as a random effect. Participants reporting lifetime pool attendance compared to those who did not showed lower odds of breast and colorectal cancer (approximately 5% lower risk). Swimming more than 10 times/month did not increase the protective association. For breast and colorectal cancer, only pool attendance outside the summer months was associated with a lower risk, whereas it was associated with increased prostate cancer risk. Findings suggest that lifetime swimming in pools may reduce breast cancer and colorectal cancer risk despite DBP exposure. These novel findings require replication.