Many people use melatonin as a sleeping aid, but perhaps they should stop. A new Danish study shows that taking melatonin during daytime lowered insulin sensitivity by about 10%, thereby disturbing glucose metabolism.
Melatonin is a natural sleep hormone secreted from the pineal gland in the brain in the absence of light. It promotes sleep, and high levels of melatonin are a starting-point for a good night’s rest.
Melatonin can also be made synthetically, and many people use it as a sleeping aid when a good book, a cup of herbal tea and counting sheep are insufficient.
In Denmark, melatonin is a prescription drug, and doctors increasingly prescribe it to children and to adults older than 55 years, but it is available over the counter in the United States, where melatonin is especially popular because many people think that taking a natural hormone is safe.
However, a new Danish study shows that this conclusion may be somewhat hasty. Melatonin can reduce insulin sensitivity, which is key to developing type 2 diabetes.
“Melatonin benefits the body at the right times of the day, but our results indicate that people should not have high concentrations of melatonin in the body during daytime because it can affect glucose metabolism. People who are already predisposed to developing type 2 diabetes could consider avoiding taking melatonin regularly until more is known about its potential impact,” explains a researcher behind the new study, Julie Støy, physician and PhD, Steno Diabetes Center Aarhus.
The research results have been published in the Journal of Pineal Research.
Melatonin, sleep and the risk of type 2 diabetes are associated
The fact that type 2 diabetes, sleep and melatonin are associated is not novel knowledge . Many studies have shown that disturbing the circadian rhythm increases the risk of developing type 2 diabetes. For example, this applies to people who work night shifts or are active nocturnally for other reasons. Both night work and a misaligned circadian rhythm increase the risk of developing type 2 diabetes, and melatonin could play a role.
“Poor sleep is as strong a risk factor for developing type 2 diabetes as being genetically predisposed by having family members with type 2 diabetes. In addition, genetic studies have also shown that genetic variants in the gene encoding the melatonin receptor predispose to developing type 2 diabetes. Much evidence indicates an association, but we need to find out how this all fits together,” explains Julie Støy.
Gave melatonin to young men and investigated metabolic functions
Julie Støy and colleagues recruited 20 healthy men 20–40 years old for the study. They took four 10-mg capsules of melatonin at 1-hour intervals during the daytime experiments. The researchers investigated how high levels of melatonin affected the concentrations of various endocrine hormones, including corticosteroids, growth hormones and sex hormones. They also examined the body’s fat metabolism, the formation of insulin in response to infusion of glucose and insulin sensitivity.
Melatonin reduced insulin sensitivity by 10%
Taking melatonin and the resulting high concentration of melatonin did not affect the production of various endocrine hormones, including insulin.
Melatonin slightly affected fat metabolism, but the most interesting result was on insulin sensitivity. Taking a large dose of melatonin during daytime reduced insulin sensitivity by about 10%.
“Reduced insulin sensitivity is absolutely key to developing type 2 diabetes, so this reduction is very interesting,” says Julie Støy.
A secondary finding was that melatonin slightly lowers blood pressure, which other researchers have also observed previously.
Investigating long-term effects of melatonin
Julie Støy says that the results are exciting because they indicate a mechanism by which taking melatonin may contribute to some people developing disturbed glucose metabolism
These people may have other risk factors, and taking melatonin to enable them to fall asleep is the last straw before blood glucose rises to a level that is too high.
This finding means that the conclusions may also be clinically relevant: that people with many risk factors for developing type 2 diabetes, such as people with a family history of type 2 diabetes and obesity, should avoid taking melatonin as a regular sleeping aid.
However, Julie Støy also says that caution should be exercised in interpreting the results of a small intervention study with 20 people under controlled laboratory conditions and a dose of melatonin that is substantially higher than what people with sleep disorders use, and because melatonin was taken at a time when the blood concentration of the hormone in daytime is usually very low.
“In view of our results and the steadily increasing prevalence of type 2 diabetes, more research within this field is highly warranted. We induced an acute increase in the melatonin concentration during the day, and this may not correspond to the effect when people take more frequent but smaller doses of melatonin over many days at bedtime to fall asleep. Melatonin can improve sleep quality and thus benefit health, and this may outweigh any possible direct and negative effect of melatonin on insulin sensitivity. We are therefore investigating this in a new study, in which we give people with type 2 diabetes a 10 mg of melatonin every night at bedtime for 3 months. But overall, we currently conclude that taking high doses of melatonin during the day does not seem appropriate,” says Julie Støy.