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VITAMIN D HOMEOSTASIS AND DIABETES MELLITUS
There are 285 million people worldwide living with diabetes. 90 – 95 % of these have type 2 diabetes. This number is expected to reach 439 million by 2030. Impaired glucose tolerance or insulin resistance, is even higher. Diabetes, of any type, makes people’ s lives hard and its care is very costly. Patients need lifelong treatment and treatment of its side effects like hypertension, hyperlipidaemia and its acute and chronic complications and its sequelae.
Genetic and environmental factors are the leading causes of diabetes. Environmental factors have been estimated to be responsible for 60-90 % of type 1 diabetes and and type 2 diabetes. Scientists have recently began to investigate the association of vitamin D to diabetes, which is considered as an enviromental factor. However, there is a huge controversy on this issue.
The vitamin D receptor( VDR) is present not only in classical target tissues such as bone, kidney and intestine, but also in many other nonclassical tissues, for example, in the immune system( T and B cells, macrophages, and monocytes), in the reproductive system( uterus, testis, ovary, prostate, placenta, and mammary glands), in the endocrine system( pancreas, pituitary, thyroid and adrenal cortex), in muscles( skeletal, smooth, and heart muscles) and in brain, skin, and liver.
Some scientists argue that decreased vitamin D homeostasis plays a role in the development of type 2 diabetes. Active Vitamin D-1,25 cholecalciferol- is a modulator of pancreatic endocrine function; insulin synthesis and secretion, it also prevents beta cell dysfunction and decreases inflammation. That’ s why, altered vitamin D homeostasis plays a role in the development of type 2 DM. The mechanisms responsible could include effects on insulin resistance, beta-cell dysfunction, the degree of
inflammation, and endothelial dysfunction( Figure 1). According to a clinical study, when 25( OH) D concentrations are found in great amounts in serum, fasting plasma glucose levels were low, because Vit D regulates insulin secretion from beta cells. Furthermore, using the hyperglycemic clamp; which is a method for quantifying insulin secretion and resistance; 25( OH) D levels were positively correlated with insulin sensitivity index.
It is also argued that in the case of hypovitaminosis D, the body perceives insulin as an antigen and destroys it, which means hypovitaminosis increases autoimmunity.“ So major questions still to be answered are whether increasing vitamin D status to the maximum seen in healthy people would reduce the risk of diabetes, the severity of the disease or its complications, including cardiovascular disease.” 7
Another report shows that hyperglycemia is reduced by prolonged vitamin D supplementation for osteomalacia in established Type 2 DM. Though, short-term supplementation has been ineffective. Furthermore, there were no beneficial effects of supplementation in Type 2 diabetes subjects who were already vitamin D replete.
1 Christy S Maxwell and Richard J Wood.“ Update on vitamin D and type 2 diabetes,” in Nutrition Reviews, Vol. 69( 5), p. 291.
2 Chander P. Arora.“ Role of vitamin D in modulating gestational diabetes.” in Biopolymers and Cell, 2011, 27: 2, p. 85