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Vitamin D supplementation does not improve insulin sensitivity, insulin secretion
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Insulin sensitivity and insulin secretion were not changed with vitamin D supplementation in adults with type 2 diabetes and vitamin D deficiency, suggesting that therapeutic vitamin D3 supplementation does not improve glucose homeostasis, according to study findings published in Diabetes Care.
Hanne L. Gulseth, MD, PhD, of the department of endocrinology, morbid obesity and preventive medicine and the Hormone Laboratory at Oslo University Hospital, and colleagues evaluated 62 adults (mean age, 55.7 years) with type 2 diabetes (mean diabetes duration, 10 years; mean HbA1c, 7.8%; mean BMI, 31.9 kg/m2) and vitamin D deficiency randomly assigned to a single dose of 400,000 IU oral vitamin D3 or placebo for 6 months to determine the efficacy of vitamin D supplementation on insulin sensitivity and insulin secretion. Participants receiving vitamin D supplementation received an additional 200,000 IU D3 after 4 weeks if serum 25-(OH)D was less than 100 nmol/L.
Mean serum 25-(OH)D levels increased from 30 nmol to 96.9 nmol and 73.2 nmol after 4 weeks and 3 months, respectively, in the vitamin D group; no significant change in mean serum 25-(OH)D was observed in the placebo group. Serum 25-(OH)D was higher in the vitamin D group compared with the placebo group (53.7 nmol/L vs. 38.2 nmol/L; P < .001) after 6 months. Over the study period, total exposure to 25-(OH)D was 1,870 nmol/L in the vitamin D group and 1,090 nmol/L in the placebo group each week (P < .001). The target serum 25-(OH) of at least 100 nmol/L after 4 weeks was reached by 48.5% of the vitamin D group.
Researchers observed no significant differences between the two groups for insulin sensitivity or glycemic control. Over the study period, no significant changes were observed in insulin secretion, fasting levels of insulin or C-peptide.
There were no important safety issues tied to vitamin D administration whereas four serious adverse events occurred in the placebo group.
“The findings complement and support those of other randomized trials that reported no significant effect of vitamin D supplementation on important glucose regulatory mechanisms, like insulin secretion and insulin action, in subjects with only moderate or no vitamin D deficiency,” the researchers wrote. “At present, we suggest that a high bolus dose of vitamin D supplementation is not recommended for this purpose.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
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