Low levels of melatonin, a hormone that helps regulate sleep cycles, may predict a person's type 2 diabetes risk.

Type 2 diabetes risk has long been linked to sleep abnormalities, and a new study conducted at Brigham and Women's Hospital (BWH) in Boston finds that low melatonin secretion is associated with increased risk for the disease. The study was published in the April 3 issue of the Journal of the American Medical Association.

Melatonin, produced by the brain's pineal gland and released into the bloodstream, plays a major role in regulating the body's daily circadian rhythm. The hormone's levels typically peak several hours after a person falls asleep, and decline until waking.

The sleep/wake cycle is related to many important bodily functions, and previous research suggested that melatonin has a role in glucose metabolism, a process that malfunctions in diabetics. According to the BWH team's background information, melatonin receptors exist in the pancreas, which produces insulin. Genetic mutations in melatonin receptors have been associated with insulin resistance and type 2 diabetes risk, and sleep deprivation has been linked to increased insulin resistance.

"This is the first time that an independent association has been established between nocturnal melatonin secretion and type 2 diabetes risk," said study coauthor Dr. Ciaran McMullan, of BWH's Renal Division and Kidney Clinical Research Institute, in a statement.

"Hopefully this study will prompt future research to examine what influences a person's melatonin secretion and what is melatonin's role in altering a person's glucose metabolism and risk of diabetes."

The study analyzed biological data from 370 women with type 2 diabetes and 370 non-diabetic women matched for age and race, all part of the Nurses' Health Study. Participants provided urine and blood samples in 2000, and researchers then tracked them over the next decade to see how many developed type 2 diabetes.

Results showed that participants with the lowest levels of nocturnal melatonin secretion had more than double the risk of developing type 2 diabetes compared with those who had the highest levels of nocturnal melatonin. Even after taking into account other type 2 diabetes risk factors like genetics, body mass index, and lifestyle factors like diet, exercise, and sleep duration, low melatonin secretion was still a significant risk factor.

25.8 million Americans have diabetes, according to the 2011 National Diabetes Fact Sheet, at an annual cost of $245 billion in medical expenses and lost productivity.

The researchers plan to investigate whether low melatonin secretion can directly cause type 2 diabetes, and what mechanisms might be at work. If there is a causal effect, melatonin supplements or more tightly controlled sleep routines might decrease insulin resistance and type 2 diabetes risk.

"Insufficient sleep, poor sleep quality, including sleep apnea, and irregular sleep-wake cycles such as those that occur in shift work have all been linked to an increased risk of type 2 diabetes," said sleep researcher Eve Van Cauter of the University of Chicago to USA Today.

"Good regular sleep habits and avoiding light exposure in the wee hours will help to produce melatonin and may reduce the risk of developing type 2 diabetes."