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Low levels of melatonin linked to diabetes

Low levels of melatonin, a hormone involved in the regulation of sleep, may boost the risk of diabetes, a new study suggests.

Over a 12-year period women, with the lowest levels of melatonin were more than twice as likely to develop type 2 diabetes, compared to those with the highest levels of the hormone, according to a report published in the Journal of the American Medical Association Tuesday.               

While the researchers expected to find some association between melatonin and diabetes risk, they were surprised by the magnitude of what they saw, said the study’s lead author, Dr. Ciaran McMullan, a research fellow at Harvard’s Brigham and Women’s Hospital.

“What we don’t yet know is whether you can change the risk of diabetes by increasing melatonin secretion,” McMullan said.

For the new study, researchers compared 370 diabetic women to 370 women without the disorder. The women came from a larger, ongoing project known as the Nurses’ Health Study. At the beginning of that study, all participants filled out surveys that questioned them about lifestyle habits, including diet, exercise, smoking history, and sleep patterns. The women were also asked to submit a urine sample, which provided a baseline melatonin level. None of the women had type 2 diabetes at the beginning of the study.

Even after the researchers accounted for lifestyle factors, including hours of sleep, women with the lowest melatonin levels were 2.2 times as likely to develop diabetes compared to those with the highest levels.

Although melatonin was found to be a predictor of diabetes risk independent of number of hours of sleep, the hormone does have an impact on the body's daily rhythms, peaking right before a person falls asleep and declining during the night. 

It's unknown whether low melatonin levels actually caused diabetes, but other research suggests that might be the case, McMullan said. Studies have shown that melatonin supplements given to diabetes-prone rats can help stave off the disease, while also improving cholesterol and triglyceride levels. 

Receptors for melatonin are found all over the body, including the pancreas, which makes insulin, he added. The presence of the hormone receptors in the pancreas suggests melatonin might have an impact on insulin production, as well as insulin resistance, McMullan said.

Still, more research is needed before recommending melatonin supplements for people with high blood sugar levels, McMullan said.

It’s entirely possible that the melatonin levels are simply an indicator of how well a person’s internal clock is working, said Dr. Mitchell Lazar, a professor of medicine and director of the Institute for Diabetes, Obesity and Metabolism at the Perelman School of Medicine at the University of Pennsylvania.

“We’ve increasingly realized that aspects of our sleep-wake cycle, our behavioral and circadian rhythms are environmental factors that contribute to the risk for diabetes,” Lazar explained. “For example, it’s been shown in many studies that people on shift work have an increased incidence of diabetes.

“Now it could be that low melatonin causes diabetes, but it could also be possible that diabetes causes low melatonin.”

The melatonin connection to diabetes is important, “but it’s just one piece of the puzzle,” Lazar said.

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