Vitamin D supplementation increases insulin sensitivity, beta-cell function
Taking 5,000 IU of vitamin D per day may improve insulin sensitivity and beta-cell function for those with prediabetes or type 2 diabetes, according to findings published in the European Journal of Endocrinology.
“Since low vitamin D status is highly prevalent worldwide, the potential role of vitamin D supplementation in improving glucose homeostasis generated great enthusiasm among scientists and clinicians,” Claudia Gagnon, MD, clinician researcher at the Centre Hospitalier Universitaire (CHU) de Québec-Université Laval in Québec City, Canada, and colleagues wrote. “However, randomized controlled trials of vitamin D supplementation have shown inconstant effects on measures of insulin sensitivity, insulin secretion and [beta]-cell function.”
Ninety-six participants (mean age, 58.7 years; 38.5% women) took part in a placebo-controlled, double-blind study at CHU de Québec-Université Laval. A daily regimen of either 5,000 IU of vitamin D3 or placebo was randomly assigned to the participants, who were all aged at least 25 years and had newly diagnosed type 2 diabetes or were considered at high risk based on waist circumference and insulin resistance indicators. All participants had a baseline serum 25-hydroxvitamin D level of 55 mmol/L or less.
The researchers assessed peripheral insulin sensitivity via M-value, which was obtained from a 2-hour hyperinsulinemic-euglycemic clamp at baseline and at 6 months from study enrollment, which took place from January 2013 to October 2016. The researchers also evaluated hepatic insulin sensitivity, whole-body insulin sensitivity, beta-cell-function and insulin secretion while participants took part in a 75-g 2-hour oral glucose tolerance test.
The average M-value for participants in the treatment group was 3.97 mg/kg/min at baseline and 4.88 mg/kg/min at 6 months vs. measures of 4.15 mg/kg/min and 4.12 mg/kg/min at baseline and 6 months, respectively, for those in the placebo group (P = .009), although the researchers noted results from those with prediabetes and type 2 diabetes primarily drove these findings. For those with prediabetes, taking vitamin D yielded a 1.25 mg/kg/min improvement in insulin sensitivity compared with a 0.56 mg/kg/min decrease in insulin sensitivity for those taking placebo (P = .015). Participants with type 2 diabetes experienced a 1.46 mg/kg/min increase in M-value after 6 months, which was higher than the 0.08 mg/kg/min increase for those taking placebo who had type 2 diabetes (P = .03).
The researchers observed no significant difference in M-values between vitamin D and placebo treatment between participants without prediabetes or type 2 diabetes. In addition, they wrote that other measures of insulin sensitivity and secretion failed to exhibit a significant difference between vitamin D and placebo regimens in all participants.
“The discordant effects of vitamin D supplementation that we observed on insulin sensitivity ... suggests that vitamin D acts mainly on peripheral insulin sensitivity,” the researchers wrote.
Although there was no observed effect of vitamin D on these other measures of insulin sensitivity, the researchers noted an increase in the disposition index for those in the vitamin D group after 6 months compared with a decrease in the placebo group (P = .039).
“Another notable finding of our study is the significant beneficial effect of vitamin D supplementation on disposition index, a measure of beta-cell compensatory capacity, with stability in the control group and improvement in the treatment group,” the researchers wrote. “Preservation of beta-cell function is important, as it was shown to predict reduced diabetes risk.” – by Phil Neuffer
Disclosures: Gagnon reports she has received research funding from the Food and Health Programmatic grant program from the Canadian Institutes of Health Research. Please see the study for all other authors’ relevant financial disclosures.