Insulin Sensitivity Not Affected by Vitamin D Supplementation in T2D

No between-group differences for factors such as glycemic control, endogenous glucose production, and insulin sensitivity were found.

Patients with type 2 diabetes mellitus (T2DM) had no significant change in insulin sensitivity or secretion after vitamin D supplementation, according to a recent study published in Diabetes Care.

Hanne L. Gulseth, MD, from the Department of Endocrinology and Morbid Obesity and Preventive Medicine at Oslo University Hospital, Norway, and fellow researchers performed a 6-month randomized, double-blinded, placebo-controlled trial with 62 men and 25 women with T2DM who received oral vitamin D3 (400,000 IU) or placebo.

“The main advantage of giving the vitamin D supplementation as 1 or 2 high doses only was to secure 100% compliance with the medication, as all interventional medication was taken under supervision,” the researchers wrote.

“Moreover, all subjects got a rapid and significant increase in 25(OH)D concentrations, which may be important to obtain the possible beneficial effects of 25(OH)D in nonskeletal tissue because local 1α-hydroxylation is suggested to demand a concentration of at least 75 nmol/L.”

The participants’ mean age was 55.7±9.5 with a body mass index of 31.9±4.9 kg/m2, a glycated hemoglobin level of 7.8%±1.4% (62 mmol/mol), and a mean baseline serum 25(OH)D of 38.0±12.6 nmol/L. After 4 weeks, patients with serum 25(OH)D at <100 nmol/L received an additional 200,000 IU D3.

The majority of participants used glucose-lowering medication (only 10 did not), and 27 were treated with insulin. In addition, 63% of patients used statins, 61% used blood pressure-lowering medications, and 32% used aspirin. Macro- and microvascular complications were reported in 8% and 16% of patients, respectively.

At 4-week follow-up, serum 25(OH)D increased to 96.9±18.3 nmol/L; at 3 months, serum 25(OH)D increased to 73.2±13.7 nmol/L, which increased to 53.7±9.2 nmol/L after 6 months. Patients in the vitamin D group had serum 25(OH)D levels of 1870±192 nmol/L per week compared with 1090±377 nmol/L per week in the placebo group (P <.001).

The researchers found there were no between-group differences for factors such as glycemic control, endogenous glucose production, and insulin sensitivity (P =.52), and there was no significant change in first-phase insulin secretion after vitamin D supplementation (P =.10).

No safety issues were noted, but there were 4 serious adverse events 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.”

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Gulseth HL, Wium C, Angel K, et al. Effects of vitamin D supplementation on insulin sensitivity and insulin secretion in subjects with type 2 diabetes and vitamin D deficiency: a randomized controlled trial [published online May 3, 2017]. Diabetes Care. doi: 10.2337/dc16-2302