Despite the fact every year millions of people discover they have type 2 diabetes, we still don’t know exactly what causes the disease. Now researchers in the US suggest it may be linked to the amount of melatonin a person secretes: in a JAMA study published online this month they show participants who secreted the least melatonin into the bloodstream during sleep had double the risk of developing type 2 diabetes.

Melatonin is a hormone that helps to control other hormones and our day-night cycle or circadian rhythm. It is made in the pineal gland in the brain and secreted into the bloodstream, peaking at night.

The up and down cycle of melatonin secretion (high at night, low during the day) is critical for a good night’s sleep. When this is disrupted, we experience disturbed sleep.

First author Ciaran McMullan, a researcher in the Renal Division and Kidney Clinical Research Institute at Brigham and Women’s Hospital in Boston, says in a statement that:

“This is the first time that an independent association has been established between nocturnal melatonin secretion and type 2 diabetes risk.”

He and his colleagues hope their findings will spur others to examine what factors affect our melatonin levels and how melatonin interacts with glucose metabolism and risk for diabetes.

For their study, they used data from a subset of 740 women taking part in the Nurses’ Health Study, one of the largest and longest running investigations of factors that influence women’s health.

370 of the women developed diabetes between 2000 and 2012, and the other 370 were matched controls who remained healthy over that period.

All the women in the subset had given urine and blood samples in 2000.

When they compared the data on the two groups, the researchers found participants with low levels of night-time secretion of melatonin had about twice the risk for developing type 2 diabetes than those whose blood samples showed they had high levels of night-time melatonin secretion.

“Women in the highest category of melatonin secretion had an estimated diabetes incidence rate of 4.27 cases/1000 person-years compared with 9.27 cases/1000 person-years in the lowest category,” they write.

Even when they took into account well-known risk factors for type 2 diabetes, such as body mass index, family history for diabetes, and a range of lifestyle factors such as exercise, diet, smoking and sleep duration, the team found the link with low melatonin was still significant.

In their conclusions they note:

“Lower melatonin secretion was independently associated with a higher risk of developing type 2 diabetes. Further research is warranted to assess if melatonin secretion is a modifiable risk factor for diabetes within the general population.

Grants from the National Institutes of Health funded the study.

Another US study published in October 2012 in the journal Sleep, suggests that the less sleep teenagers get, the higher their chance of developing insulin resistance, a metabolic condition that increases a person’s risk of developing type 2 diabetes.

Written by Catharine Paddock PhD