Diabetes mellitus:
Vitamin D deficiency has been observed in the onset of diabetes (type 1 and 2) in world populations (51). The active form of vitamin D (calcitriol) after binding with its receptor (VDR) plays an important role in insulin secretion and the insulin sensitivity in the targeted cells (52).
Some observational studies in Pakistani population showed vitamin D deficiency in type 2 diabetic subjects (53, 54). A case control study conducted in a district headquarter hospital Gujranwala, Punjab found that vitamin D levels were significantly lesser in diabetic patients as compared with control group but both groups had vitamin D levels less than 20 ng/mL (55). In another study, vitamin D levels were found negatively associated with blood glucose levels of type 2 diabetic patients in Karachi (56). Similarly, another study showed that 62% of type 2 diabetic patients had elevated levels of HbA1c and poor glycemic control along with vitamin D deficiency (57). A study was conducted by our group found that vitamin D levels were negatively correlated with random blood sugar and HbA1c levels in the diabetic patients. However, vitamin D levels were not significantly different between good and poor glycemic control subjects (58).
Elevated levels of HbA1c represent poor glycemic control and it is a common modality in type 2 diabetic patients (59). A study showed positive association of vitamin D deficiency with poor glycemic control in Pakistani population (60).
A randomized clinical trial was conducted to evaluate the effects of vitamin D administration to improve glycemic control in type 2 diabetic patients at a tertiary care hospital in Lahore, Punjab (61). Patients were divided in to two groups. One group was administered only Metformin 500 mg after dinner while, second group was administered 200,000 IU of vitamin D along with 500 mg Metformin after dinner for six months of period. The result showed improvement in vitamin D levels in the group administered with vitamin D and metformin, but HbA1c levels were not found significantly different after six months between two groups.
Vitamin D deficiency has also been studied with the relevance of dyslipidemia in type 2 diabetic patients (62). A study conducted to evaluate the role of statin use with vitamin D levels showed no significant association with dyslipidemia. But a significant negative association was found between total cholesterol and vitamin D levels suggesting an important impact of vitamin D levels with hypercholesterolemia in the type 2 diabetic patients (63).
Microvascular complications in diabetes such as retinopathy, neuropathy and nephropathy have been associated with vitamin D deficiency in world populations (64). The results of meta-analysis revealed that vitamin D deficiency is associated with the onset of diabetes neuropathy in Caucasians and Asian populations (65). Microvascular complications are prevalent in Pakistani population and Vitamin D deficiency was found to be associated with diabetic retinopathy in type 2 diabetic patients of Peshawar, KPK (66).