Vitamin D supplementation as an adjuvant therapy for patients with T2DM: an 18-month prospective interventional study

Background: Vitamin D deficiency has been associated with impaired human insulin action, suggesting a role in the pathogenesis of diabetes mellitus type 2 (T2DM). In this prospective interventional study we investigated the effects of vitamin D3 supplementation on the metabolic profiles of Saudi T2DM subjects pre- and post-vitamin D supplementation over an 18-month period. Methods: T2DM Saudi subjects (men, N = 34: Age: 56.6 +/- 8.7 yr, BMI, 29.1 +/- 3.3 kg/m(2); women, N = 58: Age: 51.2 +/- 10.6 yr, BMI 34.3 +/- 4.9 kg/m(2);) were recruited and given 2000 IU vitamin D3 daily for 18 months. Anthropometrics and fasting blood were collected (0, 6, 12, 18 months) to monitor serum 25-hydroxyvitamin D using specific ELISA, and to determine metabolic profiles by standard methods. Results: In all subjects there was a significant increase in mean 25-hydroxyvitamin D levels from baseline (32.2 +/- 1.5 nmol/L) to 18 months (54.7 +/- 1.5 nmol/L; p<0.001), as well as serum calcium (baseline = 2.3 +/- 0.23 mmol/L vs. 18 months = 2.6 +/- 0.1 mmol/L; p = 0.003). A significant decrease in LDL-(baseline = 4.4 +/- 0.8 mmol/L vs. 18 months = 3.6 +/- 0.8 mmol/L, p < 0.001] and total cholesterol (baseline = 5.4 +/- 0.2 mmol/L vs. 18 months = 4.9 +/- 0.3 mmol/L, p < 0.001) were noted, as well as a significant improvement in HOMA-beta function (p = 0.002). Majority of the improvements elicited were more prominent in women than men. Conclusion: In the Saudi T2DM population receiving oral Vitamin D3 supplementation (2000 IU/day), circulating 25-hydroxyvitamin D levels remained below normal 18 months after the onset of treatment. Yet, this "suboptimal" supplementation significantly improved lipid profile with a favorable change in HDL/LDL ratio, and HOMA-beta function, which were more pronounced in T2DM females.