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

## TL;DR

Swimming in pools may reduce the risk of breast and colorectal cancer, despite exposure to potentially harmful disinfection byproducts.

## Contribution

This study is the first to show a protective association between swimming pool attendance and cancer risk in a large multicase-control setting.

## Key findings

- Lifetime swimming pool attendance was linked to a 5% lower risk of breast and colorectal cancer.
- Swimming outside summer months was associated with reduced breast and colorectal cancer risk.
- Swimming pool attendance was linked to increased prostate cancer risk.

## Abstract

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.