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.

Although previous studies have demonstrated that royal jelly (RJ) may have estrogenic properties and prevent postmenopausal bone loss, the underlying mechanisms are not fully understood. This animal study aimed to investigate the effects of specific fatty acids of RJ, 10-hydroxy-2-decenoic acid (10H2DA) and 10-hydroxydecanoic acid (10HDAA), in ovariectomized rats. Ten-week-old female Wistar rats were divided into the Baseline, Sham, Ovx, Ovx + 10H2DA, and Ovx + 10HDAA groups. Rats in the Baseline group were sacrificed immediately, whereas those in the other groups were subjected to either a sham operation or bilateral ovariectomy. The animals in the Ovx + 10H2DA and Ovx + 10HDAA groups were fed diets containing 10H2DA and 10HDAA, respectively. Twelve weeks after surgery, the rats were sacrificed, and indices of bone mass and bone mechanics were analyzed. Femoral bone mineral density was significantly lower in the Ovx group than in the Sham group (p < 0.01). Administration of 10H2DA or 10HDAA did not ameliorate bone loss after ovariectomy. In addition, administration of these fatty acids diminished femur bone stiffness in ovariectomized rats (p < 0.01 and p < 0.05, respectively). These findings suggest that the favorable effects of RJ may not be exerted solely by 10H2DA or 10HDAA. However, these effects may be exhibited in combination with other RJ constituents.