European Journal of Cardiovascular Medicine

In the present scenario, Diabetes mellitus type II contributes to the vast burden of morbidity and mortality worldwide and yet is largely preventable and managed by a healthy lifestyle and dietary modifications.^[1] In 2018, there were more than 500 million prevalent cases of type II diabetes mellitus, the incidence increasing at an alarming rate worldwide. Presently, India has 32 million diabetic individuals and predicted to increase to 80 million by the year 2030.^[2]

Diabetes mellitus being a metabolic disorder is characterized by chronic hyperglycaemia due to impaired insulin secretion, peripheral insulin resistance, or both.^[3] To prevent long-term micro- and macro-vascular complications, patients with DM are required to maintain adequate glycaemic control, which is routinely assessed by measuring glycosylated haemoglobin (HbA1c) and fasting blood glucose (FBG) levels.^[4]

Despite being classified as a micronutrient, vitamin D has also been noted to serve several hormonal functions that are proposed to result from its action on vitamin D receptors (VDRs), which are widely expressed on various cell types. ^[3] Vitamin D deficiency can aggravate many diseases and is also linked to predisposition of diabetes and may play a role in the development of diabetes.^[5]

Vitamin D deficiency is highly prevalent in India even though we live in the temperate zone. About 70% of adults in both rural and urban areas were found showing manifestations of vitamin D deficiency.^[4] Indians outstands in the prevalence of both diabetes and Vitamin D deficiency. According to a study, vitamin D levels having been found to be inversely related to glycosylated haemoglobin levels in gestational diabetes mellitus. ^[6] Vitamin D may serve a role in peripheral insulin sensitivity through its action on VDRs expressed on human skeletal muscle and adipose tissue cells. These cells are involved in determining peripheral insulin sensitivity as they are responsible for glucose uptake in response to insulin secretion.^[7]

The present study was taken up with the aim to study the Correlation between serum vitamin D concentration and glycosylated haemoglobin (HbA1c) levels in patients with type II Diabetes mellitus.

It was a hospital-based retrospective study of Type 2 diabetes mellitus patients who had visited the hospital and were on treatment, from October 2023 to February 2024. The data of patients fulfilling the inclusion criteria were recorded. Patients with Type 2 diabetes mellitus (based on criteria of the American Diabetes Association) and without any complications due to diabetes were included in the study. Pregnant females and patients taking Vitamin D or calcium supplements were excluded from the study.

A total of 150 subjects matched the selection criteria. Their demographic characteristics, that is, the age and sex were recorded. Fasting blood sugar (FBS), postprandial blood sugar (PPBS), HbA1c, and Vitamin D levels were noted.

Based on Vitamin D levels, the subjects were divided into three groups: “Normal,” that is, patients with the Vitamin D level > 30 ng/ml, “insufficiency” with Vitamin D level in the range of 20–29 ng/ml, and “deficient state” with Vitamin D ≤20 ng/ml.

Based on HbA1c levels, the subjects were divided into two groups, that is, with HbA1c levels less than 6.5% and ≥6.5%.

The data thus generated were entered into SPSS ver.20. Wherever appropriate Chi-square test, Pearson’s coefficient correlation was used. P < 0.05 was statistically significant.

A total of 150 subjects were selected for the study, of which 74 were male while 76 were female. The subjects were in the age group of 25–75 years and their mean age was 50.02 ± 13.7 years. The mean age of males was 52.7 ± 13.4 years whereas that of females was 47.93 ± 18.5 years.

The mean Vitamin D level of the study subjects was 18.6 ± 5.09. The mean Vitamin D level in males was 19.4 while in females, it was 17.9. Only Eight subjects had Vitamin D level within normal range (i.e., >30 ng/ml). One hundred and ten subjects had a deficient level of Vitamin D (i.e., ≤20 ng/ml), among which two-thirds were female and one thirds were male. The corresponding figures for insufficient Vitamin D (20–29 ng/ml) were 24 and 8 among males and females, respectively. There was a significant association between Vitamin D level and sex of the subjects [Table 1].

A total of 124 patients out of 150 had raised HbA1c levels out of which 96 (78%) had deficient level of Vitamin D [Table 1]. The basic information on blood levels of FBS, PPBS, and HbA1c is mentioned in Table 2.

The “r” value between Vitamin D and HbA1c was – 0.176 suggesting an inverse correlation between the two parameters. There was also an inverse correlation between Vitamin D and FBS

[Table 3]. This indicates that lower the HbA1c level, higher is the Vitamin D level and vice versa.

Table 1: Association of Vitamin D with sex and HbA1c levels (n=150)

Table 2: The mean quantitative variables in patients studied (n=150)

Table 3: Correlation between Vitamin D with fasting blood sugar and glycosylated haemoglobin levels (n=150)

Figure;1 Correlation between Vitamin D levels with HbA1C levels in study group

Figure;2 Correlation between Vitamin D levels with Fasting blood glucose levels in study group

It is essential for patients with Type 2 diabetes mellitus to be aware of high prevalence of Vitamin D inadequacy and its adverse effect on glycaemic control and bone health.

About 74.3% of the patients with Type 2 diabetes mellitus were deficient in Vitamin D. This was more than Ghavan et al. ^[8] The disparity can be explained due to geographical distribution, sun exposure, and dietary habits of the study subjects. The study shows a definite negative correlation between Vitamin D and HbA1c levels. A negative correlation was also seen between Vitamin D and FBS levels in the study group. Similar findings were seen in studies done by Kotwal et al., ^[9] Mehta et al., ^[10] and Mohapatra et al. ^[11] It has been shown in various studies in the past that Vitamin D has a role in control of blood glucose levels and its utilization in the target tissues. Various animal and human studies have established the role of Vitamin D in insulin synthesis and secretion from β cells.^[7] It has been seen that glucose intolerance and insulin resistance are responsible for the development and progression of Type 2 DM. Hence, logically diabetes can be prevented to some extent by providing adequate Vitamin D supplementations, especially to high-risk population.^[12] Vitamin D has also been shown to delay the complications arising due to long-standing DM. Thus, there must be screening of all pre-diabetics and diabetic patients for Vitamin D deficiency. Vitamin D supplementation should be included in standard treatment protocol to prevent the harmful effects of Vitamin D deficiency and progression of DM. The recommended dosage of 4000 IU of Vitamin D to have these benefits is debatable and further studies are warranted in this respect. ^[13] The study has a small sample size; hence, the findings of this study cannot be extrapolated to the whole population. For this, studies with larger sample size are advocated.

There is an inverse correlation between Vitamin D and HbA1C that is also statistically significant, seen in many studies, the present study also shown the inverse correlation between Vitamin D and HbA1C, but it didn’t come statistically significant, may be due to small sample size. Hence present study cannot establish the role of Vitamin D in preventing Diabetes Mellitus, but it is highly recommended for Vitamin D screening in diabetic patients on a regular basis.

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