Impact of Menopause and the Menstrual Cycle on Oxidative Stress in Japanese Women

Although estrogen possesses both pro- and anti-oxidant properties, its overall role in oxidative stress among women remains unclear, particularly since the influence of exogenously administered estrogen during previous studies differed by dose, administration route, and estrogen type. The aim of this study was to elucidate the effects of endogenous estrogen on oxidative stress in women. Thus, we performed a non-interventional observational study of healthy postmenopausal (n = 71) and premenopausal (n = 72) female volunteers. Serum levels of derivatives of reactive oxygen metabolites (d-ROMs, which are collectively a marker of oxidative stress), as well as the biological antioxidant potential (BAP, an indicator of antioxidant capacity), were compared between (1) pre- versus post-menopausal women, and (2) premenopausal women in early follicular versus mid-luteal phases of their menstrual cycles. We found that serum d-ROMs and BAP values in postmenopausal women were significantly higher than those in premenopausal women. Moreover, the d-ROM levels were significantly correlated with serum copper concentrations. However, neither d-ROMs nor BAP values were significantly affected by the menstrual cycle phase, although changes in d-ROMs between the follicular and luteal phases were significantly correlated with copper concentration shifts. These data indicate that postmenopausal hypoestrogenism is associated with elevated oxidative stress, although regular fluctuations of estrogen levels during the menstrual cycle do not influence oxidative stress.