J Res Med Sci. 2013 Jan;18(1):47-51.
Hoseini SA, Aminorroaya A, Iraj B, Amini M.
Department of Internal Medicine and Endocrinology, Isfahan Endocrine and Metabolism Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
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.
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Note: 12 weeks is just barely long enough to restore vitamin D levels, but not make any changes.
Probably if this test had gone on for a few more weeks a significant decrease would have been observed in the insulin sensitivity index.