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Dinner Time, Melatonin and Genetics: Their Impact on Blood Sugar

A team of investigators at Massachusetts General Hospital, Brigham and Women’s Hospital, and the University of Murcia in Spain have conducted a clinical trial to look for connections between blood sugar control and the timing of meals relative to sleep.

The randomised study included 845 adults from Spain where each participant fasted for eight hours and then for the next two evenings had first an early meal, and then a late meal, relative to their typical bedtime. The investigators analysed each participant’s genetic code within the melatonin receptor-1b gene (MTNR1B) as previous research had linked the G-allele variant in MTNR1B with an elevated risk of type 2 diabetes.

The team found that melatonin levels in participants’ blood were 3.5 x higher after the late dinner. The late dinner timing also resulted in lower insulin levels and higher blood sugar levels. In the late dinner timing, participants with the MTNR1B G-allele variant had higher blood sugar levels than those without this generic variant.

“We found that late eating disturbed blood sugar control in the whole group. Furthermore, this impaired glucose control was predominantly seen in genetic risk variant carriers, representing about half of the cohort,” said Marta Garaulet, PhD, Professor of Physiology and Nutrition, Department of Physiology, University of Murcia, and lead author of the study.

The experiments revealed that the high melatonin levels and carbohydrate intake associated with late eating impairs blood sugar control through a defect in insulin secretion.

“We decided to test if late eating that usually occurs with elevated melatonin levels resulted in disturbed blood sugar control. In natural late eaters, we simulated early and late dinner timings by administering a glucose drink and compared effects on blood sugar control over two hours. We also examined differences between individuals [that] were carriers or not carriers of the genetic variant in the melatonin receptor,” said Richa Saxena, PhD, a principal investigator at the Centre for Genomic Medicine at Massachusetts General Hospital.

The authors state that for the general population, it may be advisable to abstain from eating for at least a couple of hours before bedtime.

“Genotype information for the melatonin receptor variant may further aid in developing personalised behavioural recommendations. Notably, our study does not include patients with diabetes, so additional studies are needed to examine the impact of food timing and its link with melatonin and receptor variation in patients with diabetes,” added Saxena.

Funding for the study was provided by the National Institutes of Health, the Spanish Government of Investigation and the Seneca Foundation.

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