Low estradiol levels in women of reproductive age having low sleep variation

Abstract

Higher exposure to light at night per se and through decrease in sleep duration and night shift work may suppress serum melatonin levels, which in turn may increase the reproductive hormone levels. High levels of steroid hormones, especially estrogens, may be associated with an increase of the breast cancer risk. This study investigated whether variation in the sleep duration during one entire menstrual cycle corresponds to variation in estradiol levels in healthy, urban women of reproductive age. Ninthy five regularly menstruating women ages 24-36 collected daily saliva samples for one entire menstrual cycle and recorded the number of hours of sleep per night (sleep duration). Saliva samples were analyzed for concentration of 17-ß estradiol (E2). We documented, after adjustments for sleep duration, a positive relationship between the sleep variation (coefficient of variation in sleep duration - sleep CV) and estradiol levels in women of reproductive age. Mean levels of E2 differed significantly in women from the lowest sleep CV quartile in comparison to other quartiles (p<0.001). The low sleep variation group, that is the women who sleep regularly, had mean E2 levels 60% lower than other groups. These results suggest that sleep variation significantly correlates with E2 levels, while sleep duration does not show a statistically significant relationship. According to the breast cancer development hypothesis, increasing the lifetime exposure to endogenous estrogens could result in higher risk of breast cancer.