Impact of five nights of sleep restriction on glucose metabolism, leptin and testosterone in young adult men.

Plain-language summary

This study set out to see how cutting sleep affects glucose handling and hormones in young men. Fourteen healthy men were kept in a laboratory for two nights of 10 hours in bed, then five nights of only 4 hours, then one recovery night. After the five short nights, glucose, insulin, cortisol and leptin had all risen, and SHBG (sex hormone-binding globulin, a protein made in the liver that binds testosterone in the blood) had dropped, which the authors read as part of the insulin-resistance picture, since insulin can suppress the liver's output of SHBG, and not as a change in usable testosterone. Triglycerides, a blood fat where lower is generally healthier, also fell, which the authors count as fat handling improving even as sugar handling got worse. Total testosterone did not show a significant change, and free testosterone was not measured. Two other studies here, on total sleep deprivation and on weekend catch-up sleep, share an author with this one, so the three are not independent of each other.

Key findings

• Five nights of 4 hours in bed raised glucose and insulin.
• Triglycerides, a blood fat where lower is generally healthier, fell, which the authors count as improved fat handling and the one measure that moved in a good direction.
• Cortisol and leptin rose and SHBG fell. The authors treat the SHBG drop as a marker of insulin resistance, not as proof that free testosterone changed. Free testosterone was not measured.
• Total testosterone did not show a significant change.