A Review of the Effect of Vitamin D3 Supplementation on Insulin Response in Adults With Overweight or Obesity
Abstract Objectives There is an inverse association between serum vitamin D and excess body weight, insulin resistance, β-cell dysfunction, and the risk of developing type 2 diabetes (T2DM). Given that inadequate vitamin D is common in adults with overweight or obesity, vitamin D supplementation may improve insulin response. The aim of this review was to investigate whether vitamin D3 supplementation in excess of the Recommended Daily Allowance (RDA: 600 IU/day) improves insulin sensitivity or reduces insulin resistance in adults with overweight or obesity and no prior diagnosis of T2DM. Methods A literature search was conducted using PubMed and CINAHL with the following search terms: ((vitamin D OR cholecalciferol supplement*) AND (overweight OR obes*) AND (insulin resistance OR insulin sensitivity)). The initial search generated 806 unduplicated articles. Filters and exclusions were applied; 171 articles were screened, 40 were reviewed in full-text and 5 randomized control trials published between 2015–2020 met inclusion criteria for the review. Results In all five studies, vitamin D3 supplementation in excess of the RDA for ≥3 months corrected vitamin D status, with no adverse effects, among the majority of subjects. Two studies provided a lifestyle intervention in addition to vitamin D3 at 25,000 and 50,000 IU/week for ≥3 months and significantly (p < 0.001 and p = 0.04 respectively) improved insulin sensitivity in adults with overweight or obesity and vitamin D deficiency. However, no significant effects on insulin response were observed in the other three studies. Conclusions High-dose vitamin D3 was effective in repleting vitamin D status in adults with overweight or obesity and inadequate vitamin D levels, and should be recommended per Endocrine Society clinical practice guidelines. Furthermore, vitamin D3 supplementation in excess of the RDA for ≥3 months combined with a lifestyle intervention may have a beneficial effect on insulin response in adults who are at risk for T2DM. Funding Sources None.