Type 2 diabetes is a metabolic disorder in which liver, muscle and fat cells are insensitive to the hormone insulin and/or insulin is present in insufficient amounts. Insulin controls glucose metabolism in the body. When cells are resistant to insulin, they do not take up excess glucose from the blood and glucose levels in the blood rise. Diets high in fat, a sedentary lifestyle and a genetic predisposition influence a person's risk for developing type 2 diabetes. Recent scientific evidence also suggests a link between disruptions in circadian rhythm, low melatonin levels and increased type 2 diabetes risk.
Circadian Rhythm
Circadian rhythm refers to a 24-hour light-dark cycle that is regulated by the "biological clock" in the brain. Special cells in the eyes detect light levels and in response to lower light these cells send a message to a particular area in the brain, which sends another message to the pineal gland to secrete melatonin. An article published in "Obesity Reviews" reports that several studies demonstrate that people with an altered circadian rhythm have an increased risk of developing type 2 diabetes. Additionally, sleep disorders are more prevalent in people with type 2 diabetes.
Melatonin
The pineal gland in the brain secretes melatonin during periods of darkness, so its concentrations are highest during the night and lowest during the day. Melatonin plays a major role in regulating circadian rhythm. It performs this function by activating specific melatonin receptor proteins on cells in the brain and eye. A study in the March 2006 issue of the "Journal of Pineal Research" reports that melatonin levels are decreased in type 2 diabetic patients.
Melatonin Receptors
A study in the journal "PLOS One" reports that variations in the gene that encodes for the melatonin receptor 1 protein is linked to impaired insulin secretion and glucose metabolism. This study also notes that the melatonin receptor 1 protein is present in insulin-secreting cells and possibly certain genetic variants have a direct effect on insulin secretion.
Melatonin and Insulin
A study in the April 2008 issue of the "Journal of Pineal Research" reports that melatonin stimulates insulin secretion in isolated human islets. The results of this study provide evidence that melatonin regulates insulin secretion.
Melatonin an Antioxidant
Oxidative stress is more pronounced in type 2 diabetics. The cells that produce and secrete insulin are also very sensitive to oxidative stress. Melatonin is a potent antioxidant and has been utilized to treat conditions of oxidative stress. A study in the "Journal of Pineal Research" reports that at doses of 5 mg per day melatonin significantly reduced markers of oxidative stress in elderly patients with type 2 diabetes. It is not currently known if the antioxidant activity of melatonin plays a role in modulating insulin secretion.
References
- "PLOS One"; Polymorphisms within the Novel Type 2 Diabetes Risk Locus MTNR1B Determine β-Cell Function; Harald Staiger et al.; December 2008
- "Journal of Pineal Research"; Melatonin Improves Oxidative Stress Parameters Measured in the Blood of Elderly Type 2 Diabetic Patients; K. Kedziora-Kornatowska et al.; April 2009
- "Journal of Pineal Research"; Diabetic Goto Kakizaki Rats as well as Type 2 Diabetic Patients Show a Decreased Diurnal Serum Melatonin Level and an Increased Pancreatic Melatonin-Receptor Status; E. Peschke et al.; March 2006
- "Journal of Pineal Research"; Function and Expression of Melatonin Receptors on Human Pancreatic Islets; R.D. Ramracheya et al.; April 2008
- "Obesity Reviews"; Epidemiological Evidence for the Links Between Sleep, Circadian Rhythms and Metabolism; J.E. Gangwisch; November 2009
