Insufficient sleep is a major public health concern [1], particularly among older adults [2-5] and is linked to adverse health outcomes including metabolic dysregulation, obesity, and type 2 diabetes mellitus [6-13]. Correlational studies suggest that insufficient sleep increases risk for diabetes and obesity [11, 15, 16], while interventional laboratory studies show that just a few days of sleep restriction can cause decreased glucose tolerance and insulin sensitivity [6, 12, 17, 18], as well as changes in metabolic and inflammatory hormone signalling [21-25]. However, this data comes almost exclusively from experiments in which healthy younger adults underwent relatively short exposures to sleep loss (1-7 days), and the field still lacks well-controlled in-lab studies which assess the time course of physiological changes in response to prolonged sleep restriction in older adults. Such studies are needed to address whether metabolic impairments continue progressively over weeks of sleep loss, or are eventually counteracted by allostatic adaptation. Relatedly, evidence suggests that circadian disruption, which typically accompanies sleep curtailment, has metabolic consequences that are distinct from [10, 22, 23] and may augment and interact with the effects of [24] sleep restriction. Finally, there is data to suggest that metabolic consequences of sleep restriction and circadian disruption can be reversed or ameliorated by sleep extension and circadian re-entrainment [10, 12, 29], though it is not yet understood how the extent of said recovery may vary with its timing and duration relative to sleep loss or circadian disruption. Therefore the proposed experiment will study the time course of changes in glucose tolerance, insulin sensitivity and related metabolic/inflammatory markers in healthy older adults exposed to three weeks of sleep restriction, in an inpatient setting, carefully controlling for effects of diet, exercise, and circadian disruption. Research training wil consist of data collection from the proposed study as well as data analysis (from proposed and previous studies), manuscript writing, presentation of results at meetings, and design of future projects based on findings. Academic training will comprise formal and informal coursework and attendance at seminars on topics of endocrinology and metabolism, aging research, sleep and circadian rhythms research, statistics and principles of clinical research, and research ethics. Mentorship training will be received via regular meetings with the sponsor and co-sponsor and through established training programs at the Brigham and Women's Department of Sleep and Circadian Disorders.