Effect of Escalating Oral Vitamin D Replacement on HOMA-IR in Vitamin D Deficient Type 2 Diabetics

Pakistan stands at seventh spot amongst the world having patients suffering from Type 2 Diabetes Mellitus (T2DM) with the prevalence of approximately 6.9 million in 2007.

Among the risk factors for the development of T2DM, there is a growing evidence that deficiency of vitamin D is an independent risk factor for its development and poor glycemic control. Vitamin D plays a significant role not only in secretion of insulin from the beta cells of pancreas but it also helps in decreasing the insulin resistance at the level of target cells.

Vitamin D has received an enormous attention recently. A report from Australia indicated 1 in 3 Australians are Vitamin D deficient. Reports from Pakistan have also demonstrated Vitamin D deficiency. The study conducted by Haroon Khan et al had 562 (76.2%) females while 175 (23.8%) were males. Mean age of respondents was 36.3 years (age range 15-75 years. Females had significantly lower mean Vitamin D levels (56.2%) compared to males (15.3%).

25(OH) Vitamin D is the circulating form of vitamin D which is measurable in the blood. Vitamin D insufficiency has been defined as serum 25-hydroxyvitamin D (25(OH) D) levels below 30 ng/mL and it is common among patients with T2DM. Many studies have revealed that Vitamin D3 (calcitriol) has a role in the synthesis and the secretion of insulin by receptor mediated molecular mechanisms.

Moreover Vitamin D functions are not limited to skeletal health benefits and may extend to preservation of insulin secretion and insulin sensitivity. Studies have revealed the association between vitamin D deficiency and changes in blood glucose and insulin levels as well as sensitivity of the target tissues to insulin .Cross-sectional data provide some evidence that circulating 25-hydroxyvitamin D (25(OH) D) is inversely associated with insulin resistance, although direct measurements of insulin sensitivity are required for confirmation. Available prospective studies support a protective influence of high 25(OH) D concentrations on type 2 diabetes mellitus risk. Vitamin D receptor gene polymorphisms and vitamin D interactions with the insulin like growth factor system may further influence glucose homeostasis. The ambiguity of optimal vitamin D dosing regimens and optimal therapeutic concentrations of serum 25(OH) D limit available intervention studies.