The sleep hormone melatonin could be responsible for an increased risk of type 2 diabetes in night shift workers, a study has found.
Scientists in Sweden say new experimental research shows melatonin impairs insulin secretion in people with a common gene variant.
Lead researcher Professor Hindrik Mulder, from Lund University, said: “This could explain why the risk of type 2 diabetes is greater among, for instance, overnight workers or people with sleeping disorders.”
Melatonin helps maintain circadian rhythm, part of the body’s biological clock. Levels of the hormone differ depending on the time of the day – during darkness it increases – and it is used as a sleeping drug or to prevent jet lag.
Professor Mulder added: “A third of all people carry this specific gene variant. 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.”
Back in 2009, the researchers were able to present an extensive gene mapping study showing how the gene variant of the melatonin receptor 1B, which is common in the population, increases the risk of type 2 diabetes.
The gene variant causes the level of the melatonin receptor on the insulin cell surface to increase, which makes the cells become more sensitive to melatonin and impairs their ability to secrete insulin.
They are now looking at the processes in mice and human beta cells and have completed a study of how the effects of drugs are influenced by genetic factors.
It included 23 healthy people and carriers of the gene variant in question and 22 non-carriers. They were given four milligrams of melatonin before bedtime over the course of three months.
Insulin secretion was significantly lower among those who carried the risk gene than those in the control group, the study showed.
It also showed that sugar concentration in the blood was higher among all participants after being treated with melatonin for three months but, it was especially evident in carriers of the risk gene who were unable to increase their insulin secretion.
Professor Mulder added: “It is perhaps therefore less suitable for carriers of the risk gene to work overnight shifts, as the level of melatonin will probably increase at the same time as the effects of the increase are enhanced.
“There is still no scientific support for this theory, but it ought to be studied in the future, on the basis of our new findings.”
The study was published in the scientific journal Cell Metabolism.

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