PROJECT SUMMARY The broad goal of this project is to determine the impact of the sleep fragmentation that characterizes menopause-related sleep disturbance on body fat gain in women. Obesity is highly prevalent in midlife and older women, with rates accelerating markedly after age 40, thereby increasing the likelihood of cardiovascular disease, metabolic syndrome, and diabetes after menopause. During the menopause transition, over 50% of women gain body fat, specifically abdominal visceral adipose tissue, unrelated to chronological aging. Estradiol withdrawal is thought to be responsible for these body composition changes. However, withdrawal of estradiol is unlikely to exclusively explain these changes because body fat gains are not uniform despite universal progression to hypo-estrogenism and because body fat accrues during the menopause transition, when estradiol is still produced intermittently. Experienced by almost half of women during the menopause transition, sleep fragmentation related to hot flashes may contribute detrimentally to these body composition changes. In older individuals, age-related reduction in total sleep time and increase in sleep fragmentation are linked with obesity and an adverse adipokine profile. In human and animal models, experimental sleep restriction and fragmentation induce an adverse metabolic biomarker profile linked with body fat gain and obesity, including suppression of leptin, increase of ghrelin, decrease of adiponectin, and increased hunger and caloric intake. However, the impact of sleep fragmentation characterizing the menopause transition on body fat gain and its metabolic biomarkers is not known. While lower estradiol levels and hot flashes, the primary source of sleep disruption in menopause, have been linked with an adverse adipokine profile in epidemiologic studies, the role of the highly prevalent sleep disruption associated with menopause has not been investigated. This proposal will pair an experimental sleep fragmentation paradigm with an experimental estradiol withdrawal paradigm mimicking menopause in healthy female volunteers to investigate the impact of menopause-related sleep disruption on metabolic and behavioral biomarkers of body fat gain. Forty healthy premenopausal women will be randomly assigned to inpatient sleep studies involving 3 uninterrupted nights followed by 3 experimentally fragmented nights, or the reverse order, during 3 sleep periods: 1) when estradiol is high during the mid-to-late follicular phase, 2) when estradiol is suppressed by a gonadotropin-releasing hormone agonist and hot flashes have not begun, and 3) when estradiol is suppressed and hot flashes have developed. The experimental design will enable the impact of sleep fragmentation (Aim 1), hot flashes (Aim 2), and estradiol withdrawal (Aim 3) on these biomarkers to be isolated from each other. Given the prevalence of sleep disruption during the menopause transition, this proposal will provide pivotal insights into the impact of menopause-related sleep fragmentation, hot flashes, and hormone changes on markers of body fat gain, which will inform health promotion strategies to prevent gains in body fat in midlife women.