At first glance it's hard to see a connection between sleep hormones and type 2 diabetes.
New research from Sweden's Lund University, however, found that melatonin impaired insulin secretion in certain people.
Melatonin and insulin are both hormones. Insulin regulates the blood sugar. Melatonin levels vary throughout the day depending on light levels. The hormone increases at night and helps to promote sleep.
"This could explain why the risk of type 2 diabetes is greater among, for instance, overnight workers or people with sleeping disorders,” senior author, Hindrik Mulder, MD, PhD, said in a press release.
Dr. Mulder and his team used gene mapping to identify people who have a gene variant that can be affected by melatonin.
Previous research showed that a gene variant on melatonin receptor B1 increases the risk of type 2 diabetes. The gene variant increases the effect of the melatonin receptor on insulin cells. As a result, the cells become less sensitive to insulin, which increases the risk of elevated blood sugar.
The study included 45 people. Of the participants, 23 were healthy but carried the gene variant. The remaining 22 were non-carriers.
All study participants were about the same age and had the same body mass index (BMI). BMI measures body fat with a calculation comparing height to weight. A BMI above 30 increases the risk of type 2 diabetes.
Each patient took four milligrams of melatonin before going to bed for three months.
Dr. Mulder and the research team found that those who carried the risk gene had significantly lower insulin secretion.
All of the study participants had an increase in blood sugar after three months of melatonin treatment. Those with the carrier gene, however, were much more likely to have higher blood sugars.
Previous research showed that people who work night shifts have an increased risk of type 2 diabetes.
"A third of all people carry this specific gene variant,” Dr. Mulder said in the press release. “Our results show that the effect of melatonin is stronger in them. We believe that this explains their increased risk of developing type 2 diabetes.”
The study was published in the May issue of Cell Metabolism.
Funding for the study was provided by multiple sources, including the European Foundation for the Study of Diabetes, the Swedish Research Council, the Swedish Diabetes Foundation, the Novo Nordisk Foundation and the European Research Council.
None of the authors reported a conflict of interest.