Introduction: Type 2 diabetes is a major public health problem. Recent epidemiological evidence also points to a potential association of vitamin D insufficiency with adverse metabolic risks, including that for type 2 diabetes.
Subjects and method: A double-blind randomized placebo-controlled trial was carried out. Seventy subjects with type 2 diabetes, age 30-75 years old, were randomly assigned in a double-blind fashion to two groups. One group received two capsules of calcitriol (0.25 μg 1,25-dihydroxy cholecalciferol per each capsule) per day. The second group received placebo tablets. At the beginning, middle and the end of the 12 week supplementation trial, serum glucose, insulin, calcium and phosphorous, HbA1c and 25(OH) vitamin D were measured.
Results: There was no significant difference between two groups at baseline. At the end of the study, fasting plasma glucose increased in the control group (p=0.038), while it remained unchanged in calcitriol group. Level of insulin and HbA1c increased significantly in both groups (p=0.013 and 0.0004 in treatment and control group). Regarding insulin resistance indices, there was a significant change in HOMA-IR and QUICKI in both groups (p=0.023 and 0.002 in treatment and 0.001 and <0.001 in control group respectively). Insulin secretion as assessed by HOMA-%β, remained relatively unchanged in the control group, while it increased significantly in the treatment group at the end of study (p=0.009).
Conclusion: Vitamin D supplementation attenuated the increase in glycemia, and increased insulin secretion, but had no effect on insulin resistance.