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.

A study found no improvement in glucose tolerance following the administration of two vitamin D doses with an interval of 2 weeks to thirty-seven non-diabetic, vitamin D-deficient adults.

Another study reported a randomised, controlled trial of vitamin D3, three fortnightly doses of 120 000 IU or placebo, in centrally obese Indian men. The subjects were not necessarily insulin resistant, but there was some improvement in postprandial insulin sensitivity following supplementation. A recent systematic review and meta-analysis on the role of vitamin D and calcium in type 2 diabetes conclude that 'there appears to be a relationship' but due to the paucity of data, an understanding of the mechanisms is incomplete.

This study has a novelty in the dosage and the frequency of administration of vitamin D which has not been studied yet. This study will enable to determine the impact of vitamin D replacement on insulin resistance in vitamin D deficient Type 2 diabetic patients and to find any correlation of serum levels of 25 hydroxyvitamin D levels with the degree of insulin resistance.