Eating dinner close to bedtime, when melatonin levels are high, disturbs blood sugar control, especially in individuals with a genetic variant in the melatonin receptor MTNR1B, which has been linked to an elevated risk of type 2 diabetes, according to a new study.
The study, published in Diabetes Care, was led by a team of investigators at Massachusetts General Hospital (MGH), Brigham and Women’s Hospital (BWH), and the University of Murcia in Spain.
The study was described in a news release from Massachusetts General Hospital.
For the randomized crossover study that included 845 adults from Spain, 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 also analyzed each participant’s genetic code within the melatonin receptor-1b gene (MTNR1B) because previous research had linked a variant (called the G-allele) in MTNR1B with an elevated risk of type 2 diabetes.
The team found that melatonin levels in participants’ blood were 3.5-fold higher after the late dinner. The late dinner timing also resulted in lower insulin levels and higher blood sugar levels. (This connection makes sense because insulin acts to decrease blood sugar levels.) In the late dinner timing, participants with the MTNR1B G-allele had higher blood sugar levels than those without this genetic 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,” says lead author Marta Garaulet, PhD, Professor of Physiology and Nutrition in the Department of Physiology at the University of Murcia.
Experiments revealed that the high melatonin levels and carbohydrate intake associated with late eating impairs blood sugar control through a defect in insulin secretion.
The authors note that, for the general population, it may be advisable to abstain from eating for at least a couple of hours before bedtime.