Sleep and testosterone

What the study did

In 2011, researchers at the University of Chicago published a short report in JAMA on how sleep restriction affects testosterone. Ten healthy men with an average age of 24 completed the study. They were lean and had been screened for sleep and endocrine problems.

The men first slept up to 10 hours a night in the lab. They then spent about a week sleeping around five hours a night, with bedtimes from 12:30 AM to 5:30 AM. At the end of each phase, researchers took blood samples every 15 to 30 minutes for 24 hours.

What it found

• After one week of short sleep, daytime testosterone levels were 10 to 15 percent lower.
• Levels were lowest in the afternoon and evening, between 2 PM and 10 PM.
• The men reported lower mood and vigor, and these worsened as the week of restriction went on.

The authors noted that most of the day's testosterone release in men happens during sleep, and that sleep fragmentation and obstructive sleep apnea have been linked to lower testosterone.

What it does not show

• It was small. Ten men, recruited around a campus. The authors themselves described it as a small convenience sample.
• It tested too little sleep, not extra sleep. It shows that restriction lowers levels. It does not show that sleeping more than you need raises them.
• It studied young, healthy men. The effect in older men or those with chronic mild sleep loss is not answered by this study.

What to do with this

• Aim for a consistent sleep and wake time. Major sleep organizations recommend at least seven hours for adults.
• Keep the bedroom dark, cool, and quiet, and limit alcohol and late caffeine.
• If you snore loudly or are tired despite enough time in bed, ask a doctor about sleep apnea.