Regular Melatonin Use May Lead to Type 2 Diabetes, Study Shows

Melatonin is a hormone that our bodies naturally produce. It helps regulate our circadian rhythm so that we can stay awake during the day and fall asleep at night. However, many people also take extra melatonin as a supplement to help them fall asleep faster and stay asleep longer if they struggle with insomnia.

Until recently, it was believed that melatonin was not only helpful for sleep but also completely safe to use. However, recent evidence suggests that this might not be the case—on either count.

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New research has uncovered that melatonin doesn’t appear to work as well as people assume it does. Meta-analyses of melatonin use show that people who take it fall asleep only about four minutes faster than people taking a placebo, and they sleep only about 10-15 minutes longer on average.

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But despite the lack of evidence that melatonin is useful, many people are still comfortable taking it—and many doctors are still comfortable recommending it—simply because it has always been believed to be safe. However, new research shows that taking melatonin might be less safe than we believe it is.

Marta Garaulet and Jingyi Qian from the Medical Chronobiology Program at Brigham and Women’s Hospital, Boston, were the lead authors of the study, which was published in the journal Trends in Endocrinology and Metabolism. Along with researchers from Harvard, MGH, and the Broad Institute, they investigated the contradictory data surrounding melatonin supplementation and found that it can impair glucose tolerance, leading to type 2 diabetes.

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More specifically, those people who took melatonin during the day experienced impaired glucose tolerance. Those who took the supplement in the evening did not see the same result unless they also tended to eat late in the evening. It appears, therefore, that melatonin affects the body’s glucose and insulin response to meals.

Standard doses of melatonin were also found to cause “plasma melatonin levels to remain 10-fold higher than physiological peak levels even 6 [hours] after administration, which could result in elevated melatonin levels the following morning.” This suggests that taking a melatonin supplement at night and then eating early in the morning could impair glucose tolerance and contribute to the development of diabetes.

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Garaulet and Qian also believe there may be a genetic element at play. Those people who have a mutated MTNR1B gene often have higher fasting blood glucose levels and are therefore at higher risk of developing type 2 diabetes. Again, melatonin use seems to increase this risk, particularly when people ate at times when their melatonin was high, such as at night or early in the morning.

“We have shown that consuming a late versus an early dinner, which was associated respectively with high and low melatonin concentrations, impairs glucose tolerance in MTNR1B risk allele carriers but not in noncarriers,” the study states.

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Of course, this doesn’t mean that melatonin supplementation doesn’t work for everyone or that you shouldn’t ever consider trying it. It just means that you should be extra cautious about it, watching out for the early warning signs of type 2 diabetes and talking to your doctor about the risks and benefits of the supplement. You should also be aware that it might not be the cure-all for your insomnia, so stop taking it if it doesn’t seem to do much for you.

If you do decide to take melatonin supplements, you can mitigate the glucose impairment by making sure you’re not eating near the time that you take your supplement. Don’t eat in the evenings or very early in the morning, and only take melatonin at night.

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