Sleep duration and biomarkers of fecundity in young men: a cross-sectional study from a population-based cohort.

Plain-language summary

This study looked at whether sleep duration affects markers of male fertility in young men. It analyzed 1,055 Danish men who reported their sleep habits and gave semen and blood samples, with testicle size also measured. Men sleeping outside the recommended 6 to 9 hours a night had slightly higher testosterone, a slightly higher free androgen index (the share of testosterone available for the body to use) and slightly more sperm with immature DNA, but all three differences were small and none of them was clear cut, so this study on its own does not establish any of them. The shape of the pattern was the more interesting result: both short and long sleep sat on the same side, and semen volume tracked with sleep in a straight line.

Key findings

• Men sleeping outside 6 to 9 hours had 5% more sperm with immature DNA, though that difference was not clear cut.
• They also had 3% higher testosterone and a 6% higher free androgen index (the share of testosterone available for the body to use), and neither difference was clear cut either.
• Both short and long sleep sat on the same side of each of those markers, so the pattern bends in both directions rather than running one way.
• Semen volume and SHBG (sex hormone-binding globulin, a protein that binds testosterone and holds it out of use, so a higher level leaves less testosterone free and usable) both tracked with sleep duration in a straight line, and the share of normally shaped sperm followed an upside-down u.