Inverse U-shaped Association between Sleep Duration and Semen Quality: Longitudinal Observational Study (MARHCS) in Chongqing, China.

Plain-language summary

This study looked at how sleep duration relates to semen quality and reproductive hormones in young men. It recruited 796 male college students in Chongqing, China and followed up 656 of them a year later, collecting semen and blood each time. Sleeping more than 9 hours went with clearly lower readings, a 21.5% smaller semen volume and a 39.4% lower total sperm count. Sleeping 6.5 hours or less pointed the same way, but those estimates were not clear cut and were wide enough to include no difference at all. The best readings sat at 7 to 7.5 hours a night, men who moved toward that range over the year improved on both measures, and the overall curve held independently of sleep quality and was reproduced in a separate group of 1,346 men. Sleep duration showed no relationship at all with reproductive hormones.

Key findings

• Semen volume and total sperm count were highest at 7 to 7.5 hours of sleep a night, and fell away on both sides of it.
• Sleeping more than 9 hours was the clear-cut half: 21.5% less semen volume and 39.4% lower total sperm count.
• Sleeping 6.5 hours or less pointed the same way, but neither estimate was clear cut and both were wide enough to include no difference.
• Men who shifted their sleep toward 7 to 7.5 hours over the year improved on both measures.
• Sleep duration showed no relationship with reproductive hormones.