Sleep Duration Is Associated With Testis Size in Healthy Young Men

Study Objectives: Sleep is increasingly recognized to influence a growing array of physiological processes. The relationship between sleep duration and testis size, a marker of male reproductive potential, has not been studied. Methods: This was a preliminary cross-sectional analysis of the baseline data from 92 healthy men (mean +/- standard deviation, age 33 +/- 6 years, body mass index [BMI] 24.7 +/- 6.1 kg/m(2)), of whom 66 underwent at-home actigraphy and 47 underwent in-laboratory polysomnography. Sleep duration and architecture were measured by actigraphy and polysomnography, testicular volume by Prader orchidometer, total testosterone by liquid chromatography tandem mass spectrometry, free testosterone by equilibrium dialysis, and luteinizing hormone and follicle-stimulating hormone (FSH) by immunochemiluminometric assay. Results: Sleep duration was correlated with testicular volume (r = .31, P = .046) and with FSH (r = -.30, P = .035), and rapid eye movement sleep was correlated with FSH (r = .44, P = .006). The significance of these findings did not change after adjustment for age and BMI, and were confirmed nonparametrically by resampling. A putative inverse U-shaped relationship between testicular volume and sleep duration was observed by polynomial regression (P = .049), but not with resampling (P = .068). Conclusions: There is a positive linear and a possible inverse U-shaped relationship between sleep duration and testis volume. Longitudinal or interventional studies manipulating sleep are required to better define causality, and ultimately to establish how much sleep is needed to maximize male reproductive potential.