Nearly all of us probably get too little sleep, mainly because we are seduced every day by the technology around us. It enables us to generate light at night, provides us with 24-hour entertainment and information through electronic media, and makes it possible for us to have contact with each other whenever we want. Every evening, when our body tells us that it’s time to sleep, we can also do a thousand other things instead.
Sleep & hormones
Too little sleep messes up our hormone balance. It makes our body less sensitive to insulin for example. Dutch researchers recently showed that after just one night of four hours’ sleep, young men’s insulin sensitivity went down by twenty percent [J Clin Endocrinol Metab. 2010 Jun; 95(6): 2963-8.] and that of diabetics by a quarter. [Diabetes Care. 2010 Jul;33(7):1573-7.]
In the latter case, lack of sleep is clinically relevant, so doctors could advise diabetics who react insufficiently to their medicines to get more sleep. “Sleep duration might become another therapeutic target to improve glucoregulation in type 1 diabetes”, the Dutch researchers say.
Sleep & testosterone
Testosterone is also affected by amount of sleep. That’s not so strange, as our bodies make much more testosterone when they’re asleep than when they’re awake. [J Clin Endocrinol Metab. 2005 Aug; 90(8): 4530-5.] We’ve taken the figure below from the study mentioned here. It shows how much testosterone is present in the blood of 22-32 year-old men while asleep and during the rest of the day.
The better men sleep, the higher their testosterone level rises while they are asleep. [J Clin Endocrinol Metab. 2001 Mar; 86(3): 1134-9.]
In the average male over forty, the testosterone level goes down by 1-2 percent per year, but researchers occasionally come across men in their eighties with a testosterone level you’d expect in a young man. Add to that the fact that many older men – but not all men – sleep less and less deeply as they get older, then you automatically think of the idea that Plamen Penev wanted to test in his study: does the testosterone level decrease in older men because they sleep less?
More sleep can double your testosterone level
Penev based his theory on, among other things, research done by Eve Van Cauter, a sleep researcher at the University of Chicago who has celebrity status in the field of endocrinology. Van Cauter discovered early in the 21st century that men in their forties make less testosterone while sleeping than men in their twenties.
Penev measured the amount of testosterone 12 slim, healthy, non-smoking men aged between 64 and 74 had in their blood in the morning. He also got the men to wear a small gadget around their wrist, which enabled him to see how many hours per night the men slept. That varied from 4.5 to 7.5 per 24 hours. The longer the men slept, the figures below show, the more testosterone there was circulating in their blood.
The men that slept the least had a testosterone level of 200-300 ng/dl. That’s a normal amount for men of this age, but it’s on the low side. The men in the study who slept the most had a testosterone level that was twice as high: 500-700 ng/dl. That’s a level you’d expect in healthy young men.
“These findings suggest that complaints of poor or insufficient sleep in otherwise healthy older men can be associated with a more pronounced age-related androgen decline”, writes Penev. “Eliciting such sleep complaints in the physician’s office may facilitate the judicious interpretation of lower testosterone levels in the older male patient.”
Before men consider doing testosterone therapy, they might first measure the amount of sleep they get. And ‘measuring’ is different from ‘guessing’ or ‘estimating’. Most people overestimate the number of hours that they sleep. This was also the case in Penev’s study. The men thought that they slept seven and a quarter hours per day on average, but Penev’s recordings showed that they only slept six hours a day.
Association between sleep and morning testosterone levels in older men.
The circulating testosterone levels of healthy men decline with advancing age. This process is characterized by considerable inter-individual variability, the causes of which are of significant biological and clinical interest but remain poorly understood. Since sleep quantity and quality decrease with age, and experimentally-induced sleep loss in young adults results in hormonal changes similar to those that occur spontaneously in the course of aging, this study examined whether some of the variability in circulating testosterone levels of older men can be related to objective differences in their sleep.
General community and university clinical research center.
Twelve healthy men ages 64 to 74 years.
Three morning blood samples were pooled for the measurement of total and free testosterone. In addition to overnight laboratory polysomnography, wrist activity monitoring for 6-9 days was used to determine the amount of nighttime sleep of the participants in everyday life settings.
MEASUREMENTS AND RESULTS:
The main outcome measures were total sleep time and morning testosterone levels. Sleep time in the laboratory was correlated with the usual amount of nighttime sleep at home (Pearson’s r = 0.842; P = 0.001). Bivariate correlation and multiple linear regression analyses revealed that the amount of nighttime sleep measured by polysomnography was an independent predictor of the morning total (Beta 0.792, P = 0.017) and free (Beta 0.741, P = 0.029) testosterone levels of the subjects.
Objectively measured differences in the amount of nighttime sleep are associated with a significant part of the variability in the morning testosterone levels of healthy older men.
PMID: 17520786 [PubMed – indexed for MEDLINE]