Association between serum 25-hydroxyvitamin D, hemoglobin A1c and fasting blood glucose levels in adults with diabetes mellitus

Abstract

In the present study, the aim was to investigate the association between serum 25-hydroxyvitamin D concentration and measures of glycemic control including hemoglobin A1c (HbA1c) and fasting blood glucose (FBG) in adult patients with diabetes mellitus (DM) from the north of Jordan. Another aim was to compare serum levels of 25-hydroxyvitamin D between patients with good glycemic control and patients with uncontrolled DM. This was a cross-sectional study that included 261 participants with DM. The concentration of 25-hydroxyvitamin D was measured using electrochemiluminescence immunoassay, HbA1c was measured using turbidimetric inhibition immunoassay and FBG was measured using the hexokinase method. Data regarding other clinical variables were obtained from medical records or by self-reporting. Participants with good glycemic control exhibited significantly higher levels of 25-hydroxyvitamin D compared with participants with uncontrolled DM (P=0.03). Participants with sufficient vitamin D status (>30 ng/ml in serum) exhibited significantly lower HbA1c level compared with participants with deficient vitamin D (<20 ng/ml) status (P=0.02). Correlation analysis determined significant inverse correlations between 25-hydroxyvitamin D levels and HbA1c and FBG levels (r=-0.23 and -0.17, respectively, both P<0.01). There were also significant correlations between duration of DM and HbA1c and FBG levels (both r=0.21, P<0.01). HbA1c level was also inversely correlated with participants' age (r=-0.19, P<0.01). Further multiple linear regression analysis revealed an inverse significant association between HbA1c and 25-hydroxyvitamin D levels (F=12.95, R²=0.48, P<0.01) but did not identify a similar association between FBG and 25-hydroxyvitamin D levels. These findings may encourage further research to identify if vitamin D supplementation may improve measures of glycemic control, and how vitamin D may affect glucose homeostasis in patients with DM.

Keywords: diabetes mellitus; glycemic control; hemoglobin A1c; vitamin D.

Figure 1.

Association between serum 25-hydroxyvitamin D, HbA1c and FBG levels in adults with diabetes mellitus. (A) HbA1c and FBG levels in participants according to vitamin D status. HbA1c level in participants with sufficient vitamin D (>30 ng/ml) was significantly higher than the level in participants with deficient vitamin D (<20 ng/ml). There was no significant difference in HbA1c level between participants with insufficient vitamin D (20–30 ng/ml) and participants with either sufficient or deficient vitamin D. In addition, there was no significant difference in FBG level between participants with sufficient, insufficient or deficient vitamin D. Data is expressed as mean ± standard deviation. (B) Significant correlation between HbA1c and FBG levels and significant inverse correlations between 25-hydroxyvitamin D and HbA1c and FBG levels. *P=0.02. HbA1c, hemoglobin A1c; FBG, fasting blood glucose.