A study published in the Journal of the American Medical Association (JAMA) shows that inadequate secretion of melatonin is associated with an increased risk of type 2 diabetes. The risk was more than double in those with the lowest levels.
Melatonin (N-acetyl-5 methoxytryptamin) is naturally produced by the pineal gland from tryptophan, an essential amino acid present in food and supplements.
Melatonin levels are directly linked to the sleep/wake cycle and in particular to alternating light and dark. Melatonin, levels of which are between 5 and 15 times higher during sleep than during the day, maintains the body’s circadian rhythms. In general, melatonin production starts at around 9.00pm, peaking in the middle of the night between 1.00am and 3.00am, before becoming undetectable by 9.00am.
Melatonin supplementation is therefore often used to prevent or treat sleep problems and insomnia.
Melatonin and diabetes
Biologically, melatonin receptors are found in the pancreas, and insulin receptors in the pineal gland. Ingesting melatonin has been shown in animals to be protective against diabetes and to even improve the lipid profile (cholesterol and triglycerides). Some longitudinal human studies have also found a link between low plasma melatonin and metabolic syndrome and diabetes.
« This is the first time a link has been established between nocturnal melatonin secretion and risk of type 2 diabetes.”
A review of data from the US Nurses’ Health Study, published in the JAMA, has just confirmed findings from animal studies and limited clinical studies showing that the lowest nocturnal melatonin levels are associated with a risk of diabetes twice that of the highest levels.
Researchers identified 370 women of the same age and ethnicity who had developed type 2 diabetes, and 370 other women from the same cohort with no sign of disease.
From data collected since the beginning of the study in 2000, they compared morning urine samples, specifically the 6-sulfoxymelatonin (melatonin’s major metabolite)/creatinine ratio, in order to estimate melatonin secretion.
They observed that melatonin secretion varied considerably between participants, the highest levels being almost five times higher than the lowest.
Those subjects with diabetes had low nocturnal melatonin levels compared with healthy participants. According to the researchers, low nocturnal melatonin secretion increased the risk of developing diabetes by 2.17 times. Conversely, sensitivity to insulin, a key hormone in regulating blood sugar and weight, was greater among women with the highest levels of melatonin.
This link was established after taking into account other factors known to promote diabetes such as obesity, family history and lifestyle (diet, physical exercise, smoking and sleep duration).
The authors estimate that “while the effects of endogenous melatonin on glucose metabolism in humans are unknown, animal data and human gene studies suggest that low melatonin secretion, or reduced cell signalling, can alter insulin sensitivity and promote type 2 diabetes”.
Dr Ciaran McMullan, one of the review’s researchers, hoped that “this study would lead to other research into the effects of melatonin secretion on the body and the role of this hormone on glucose metabolism and risk of diabetes”. He added that “additional studies are needed to determine to what degree the increase in endogenous melatonin secretion (through prolonged exposure to nocturnal darkness) or exogenous melatonin from supplementation could increase insulin sensitivity and reduce incidence of type 2 diabetes”.
This new review thus highlights considerable data suggesting the effects of poor sleep. The connection had already been made with cardiovascular health (HTA, heart failure) and this now confirms such a link for diabetes ..,
McMullan CJ, Schernhammer ES, Rimm EB, Hu FB, Forman JP. Melatonin secretion and the incidence of type 2 diabetes. JAMA. 2013 Apr 3;309(13):1388-96.