Effect of soy isoflavone supplementation on markers of oxidative stress inmen and women

Dietary intake of soy has been linked with decreased cancer risk, and the a ctive compounds in soy that have been identified include the isoflavones ge nistein and daidzein. Since these compounds have antioxidant properties, we examined levels of oxidative damage in blood of six women and six men befo re and during soy supplementation using Novasoy tablets. Blood samples were obtained at weekly intervals for 3 weeks from the women taking 50-mg isofl avones once daily and the men taking 50-mg isoflavones twice daily. Plasma levels of genistein and daidzein increased after supplementation with maxim al levels occurring at 2 weeks for the women while levels in men kept incre asing over the 3 weeks of study. There was wide variation between individua ls in the levels of isoflavones achieved. Mean levels of 5-hydroxymethyl-2' -deoxyuridine (5-OHmdU) in DNA from nucleated blood cells decreased after I week of supplementation in the women, with a decrease of 47% in mean 5-OHm dU levels after 3 weeks. In men, mean 5-OHmdU levels did not decrease until after 3 weeks of supplementation, at which there was 61% decrease. Mean pl asma levels of 8-isoprostanes were not changed appreciably in either men or women. These pilot results suggest that soy isoflavone supplementation dec reases levels of oxidative DNA damage in humans, and this may be a mechanis m behind the cancer-preventive effects of soy isoflavones. (C) 2001 Elsevie r Science Ireland Ltd. All rights reserved.