The effects of oral vitamin D on insulin resistance in pre‑diabetic patients

Background: some epidemiological and interventional studies have shown the role of vitamin d on insulin secretion and resistance. a previous study in our center showed that intramuscular vitamin d decreases insulin sensitivity in pre‑diabetic patients. we investigated the role of oral vitamin d on the insulin sensitivity index and insulin resistance in pre‑diabetic patients. materials and methods: in a randomized clinical trial, we divided 45 people with pre‑diabetes aged 47.4 ± 6.6 (range 33-61) years into three groups: group a subjects treated with 50,000 iu oral vitamin d and 500 mg calcium carbonate (n = 21), group b subjects treated with a single 300,000 iu intramuscular vitamin d and 500 mg calcium carbonate (n = 9), and group c subjects treated with 500 mg calcium carbonate alone (n = 15). serum 25‑hydroxyvitamin d [25(oh) d] was measured at baseline. if it was less than 75 nmol/l, 50,000 iu vitamin d was given weekly, and if serum 25(oh) d was more than that, vitamin d was administered every 2 weeks. before and after 12 weeks of treatment, a 75‑g glucose tolerance test was performed. we used paired t‑test and analysis of variance (anova) to analyze the data. p values less than 0.05 were considered significant. results: mean (sd) of serum vitamin d increased from 77.5 ± 39.2 to 118.8 ± 56.3 nmol/l (p = 0.009) in group a and from 80 ± 36 to 102.8 ± 43.3 nmol/l (p = 0.053) in group b, and decreased from 44.8 ± 18.3 to 34.6 ± 13.9 nmol/l (p = 0.06) in group c. insulin sensitivity index (matsuda) decreased from 11.4 ± 3 to 9.9 ± 3.2 (p = 0.046) in group a, but in comparison with other groups, it was not significant. conclusion: oral vitamin d had no effect on insulin sensitivity in pre‑diabetes patients in 12 weeks treatment. a randomized double‑blind study with a longer duration of treatment is suggested to investigate the effect of vitamin d on insulin resistance.