Abstract
OBJECTIVE: Low testosterone in men increases the risk for various disorders. Severe sleep restriction (SR) may reduce testosterone, but the effects of long-term short sleep are unknown. This study tested the effects of SR on circulating testosterone in healthy young men. DESIGN: Randomized controlled studies of SR vs habitual sleep (HS) in inpatient (study 1, n=14) and outpatient (study 2, n=13) settings. METHODS: Study 1 involved severe, acute SR (4 hours time in bed [TIB]) vs HS (9 hours TIB) for 5 nights; study 2 consisted of mild, long-term SR (HS 1.5 hours of sleep/night) vs HS for 6 weeks. Plasma testosterone levels were measured at baseline and end point (study 1) or baseline, week 3, and week 6 (study 2) of each phase. Linear model analyses to assess the effects of SR on testosterone were performed separately for each study. RESULTS: Study 1: There were no significant sleep-time interaction on testosterone concentrations (change in testosterone levels during HS = 22.86 ± 163.79 ng/dL; SR = 43.73 ± 159.96 ng/dL, P = .41) and no main effect of sleep duration (P = .13). Study 2: There were a trend for a sleep-time interaction (P = .067) and a main effect of sleep on testosterone concentrations from 6 weeks of SR (P = .0046). Testosterone concentrations were slightly lower but increased over time with SR relative to HS. CONCLUSIONS: Sleep restriction does not adversely affect plasma testosterone levels in healthy young men. Given prior contradicting evidence, confirmatory studies should be done to ascertain the influence of sleep duration and quality on testosterone concentrations in men throughout life.