Swimming is generally considered an excellent form of exercise, and indoor swimming is common, especially in winter. However, there is evidence that swimming in a chlorinated indoor pool can cause respiratory irritation or genotoxicity in some people.A recent study suggests another possible consequence: altered levels of hormones in boys.The study population consisted of 199 primarily white boys aged 14-18 years who swam regularly in indoor and/or outdoor chlorinated pools, and 162 similar boys who swam most frequently in an indoor pool disinfected with copper-silver ioniza-tion (but also swam at times in indoor or outdoor chlorinated pools). The authors compared serum levels of several testicu-lar hormone biomarkers between the two groups: inhibin B, total and free testosterone, sex hormone-binding globulin, luteinizing hormone, follicle-stimulating hormone, and dehydroepiandrosterone sulphate.The boys who swam the most in indoor chlorinated pools had concentrations of inhibin B and total testosterone about 20% lower than those of boys who swam in the pool disinfected with copper-silver ioniza-tion, and the former were about 3 times more likely than the latter to have abnormally low concentrations of these hormones. The effects were more pronounced for exposure before age 7 than before age 10 (after which no significant changes were seen), and adverse effects were associated with swimming as little as 30 minutes every 2 weeks.
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