Type 2 DM is associated with several macrovascular and microvascular complications which lead to high morbidity and mortality. It’s more important to achieve good glycemic control which helps in reducing the complications associated with DM. To achieve good glycemic control and to decrease the complications of DM, diabetes patients should follow strict dietary control, regular exercise, adherence to medication, and regular monitoring of glucose levels. [1]. As worldwide commonly used markers for monitoring glycemic control include fasting blood sugar (FBS), postprandial blood sugar (PPBS), glycosylated haemoglobin (HbA1c).

In addition to these markers, fructosamine, glycated albumin, and 1, 5‑anhydroglucitol are also used as markers of glycemic control. [2]. Vitamin D is a fat-soluble vitamin that is synthesized from 7‑dehydrocholesterol in the skin upon exposure to ultraviolet B rays of sunlight. 1,25‑dihydroxycholecalciferol which is the active form of Vitamin D plays an important role in the maintenance of calcium homeostasis by binding to its receptors on its target tissues which include bone, kidney and intestine. In addition to its role in maintaining bone health, Vitamin D has several important extra skeletal biochemical functions in the body, including its role in type 1 and type 2 DM. [3]. Vitamin D was shown to be associated with type 2 DM through its effects on insulin secretion, insulin sensitivity and systemic inflammation, which are the three major mechanisms underlying the development of type 2 DM. [4].

Data from cross-sectional as well as longitudinal studies suggest that Vitamin D deficiency has a causal role in type 2 DM. [5,6]. Moreover, a high prevalence of Vitamin D deficiency in diabetes patients has also been reported earlier. [7‑9]. Owing to its effects on insulin sensitivity, Vitamin D is suggested to have a presumptive role in glycemic control. However, studies exploring the relationship between Vitamin D levels and glycemic control in type 2 diabetes patients reported varied findings. [10‑12]. In this background, we were interested to evaluate the association between serum Vitamin D levels and Hba1c l in patients with type 2 DM.

The study was conducted during the period from Jan 2019 to Dec 2019 in SVMCH&RC –Pondicherry.

Table 1 Age/sex distribution of the study population

In our study, we had the youngest patient with 18years and the oldest patient with 78years. In the present study, we had maximum patients in the age group between 41 to 50 years as similar to various other studies. In our study male was 68% with females were 38%.

Table 2 HbA1c distribution of the study population

In the present study, we estimated HbA1c for the identification of glycemic control which is to be identified as the most appropriate method. We identified a wide range with the lowest as 6.6% to 12.8% being the highest value. A maximum of 52% was in the range of 7.1 to 8% which is identified as fair control.

Table 3 (a) Distribution of vitamin D levels among the study population

Table 3(b) Vitamin D levels among the study population

In the present study, we estimated vitamin D levels in all subjects and categorization was done as <20 and more than 20 ng/dl.48% of patients had vitamin D levels below 20ng/dl.

We did not find a statically significant correlation between HbA1C and 25(OH) D, similar to other previously published studies. [17,18,19,20,21,22]. However glycemic control was not associated with vitamin D when we controlled for confounding factors, as verified by Luo et al. and Al-Shoumer et al. [23,24]. In a study done by Figenia Kostoglou-Athanassiou et al observed, lower 25(OH) D3 levels were observed in diabetes mellitus type 2 patients than in non-diabetic controls. Vitamin D was shown to be associated with beta-cell function and insulin sensitivity in individuals at risk for DM and thus might play a role in the pathogenesis of type 2 DM. [25]. However, in a recent multicenter, randomized control trial [26]. It was reported that supplementation with 4000 IU/day of Vitamin D3 increased Vitamin D levels but did not lower the risk of DM compared to placebo after a median follow‑up of 2.5 years. Since the physiological role of Vitamin D in pancreatic beta-cell function and insulin sensitivity is well appreciated, and considering that almost 48% of the diabetes patients in the present study are Vitamin D deficient, it is suggested that Vitamin D levels are measured in these patients to identify hypovitaminosis D. Although it is not clear whether Vitamin D supplementation improves glycemic status, improvement in Vitamin D levels in diabetes patients might help in improving the overall health of the individuals along with an increase in Vitamin D levels. Simple measures such as dietary changes and lifestyle modifications along with Vitamin D supplementation may help in achieving normal Vitamin D levels in DM patients. All the measurements in the diabetes patients in the present study were done at a single time point which forms a limitation of the present study. Considering the beneficial role played by Vitamin D on glucose homeostasis, the relationship between Vitamin D levels and glycemic control needs to be explored in further large, well-controlled studies with higher population and multicentric.

In conclusion, we have identified a negative correlation concerning vitamin D levels when compared with HbA1c statically. Since the physiological role of Vitamin D in pancreatic beta-cell function and insulin sensitivity is well appreciated, and considering that almost 50% of the diabetes patients in the present study are Vitamin D deficient, it is suggested that Vitamin D levels improve the glycemic status in type 2 diabetes mellitus patients.