TUESDAY, April 2 (HealthDay News) -- Decreased levels of the hormone melatonin may be linked to the development of type 2 diabetes, according to new research.

A study of U.S. women found that those with the lowest levels of melatonin had more than twice the risk of type 2 diabetes compared to women with the highest levels of the hormone. This association held true even after the researchers controlled for other risk factors for type 2 diabetes, such as body weight and dietary habits.

But whether too little melatonin actually causes type 2 diabetes isn't clear. "We found an association between melatonin and type 2 diabetes; what we haven't got from this study is causality," said study lead author Dr. Ciaran McMullan, a research fellow at Brigham and Women's Hospital in Boston. "That's the next step of research."

The findings shouldn't change clinical management. "There's no evidence that taking melatonin will improve someone's chances of avoiding diabetes," McMullan said.

Results of the study, which was funded by the National Institutes of Health, appear in the April 3 issue of the Journal of the American Medical Association.

Melatonin is a hormone most commonly linked to sleep and the body's biological clock. The production of melatonin peaks about three to five hours after you fall asleep in the dark, and almost no melatonin is produced during the day, according to background information in the study. Sleep disruptions can affect melatonin production, as can exposure to more or less daylight, McMullan said.

People with type 2 diabetes, by far the more common form of diabetes, don't make enough insulin or use it properly. Insulin is a hormone needed to convert sugar (glucose) from foods into energy.

Melatonin receptors are found throughout the body, including in the islet cells of the pancreas, which produce insulin. This connection suggests melatonin may also play a role in glucose metabolism, according to the study.

McMullan and his colleagues reviewed data from the U.S. Nurses' Health Study. The researchers found 370 women who developed type 2 diabetes during the study period, from 2000 to 2012. They also selected 370 women without diabetes for comparison. Melatonin levels were obtained through urine samples.