Background: The role of vitamin D in people at risk for type 2 diabetes remains unclear. Aim: To evaluate whether the administration of vitamin D reduces the risk of diabetes in people with prediabetes. Data sources: PubMed, Embase, and ClinicalTrials.gov from database inception to December 9, 2022. Study selection: Eligible trials that were designed and conducted specifically to test the effects of oral vitamin D versus placebo on new-onset diabetes in adults with prediabetes. Data extraction: The primary outcome was time to event for new-onset diabetes. Secondary outcomes were regression to normal glucose regulation and adverse events. Prespecified analyzes (both unadjusted and adjusted for key baseline variables) were performed according to the intention-to-treat principle. Data synthesis: We included three randomized trials evaluating cholecalciferol, 20,000 IU (500 mcg) per week; cholecalciferol, 4000 IU (100 mcg) daily; or eldecalcitol, 0.75 mcg daily, versus equivalent placebos. The trials had low risk of bias. Vitamin D reduced the risk of diabetes by 15% (hazard ratio, 0.85 [95% CI, 0.75 to 0.96]) in adjusted analyses, with an absolute risk reduction at 3 years 3.3% (CI, 0.6% to 6.0%). The effect of vitamin D did not differ in the prespecified subgroups. Among participants assigned to the vitamin D group who maintained a mean intra-assay serum 25-hydroxyvitamin D level of at least 125 nmol/L (≥50 ng/mL) compared with 50 to 74 nmol/L (20 to 29 ng /mL) during follow-up, cholecalciferol reduced the risk of diabetes by 76% (hazard ratio, 0.24 [CI, 0.16 to 0.36]), with an absolute risk reduction at 3 years 18.1% (CI, 11.7% to 24.6%). Vitamin D increased the likelihood of regression to normal glucose regulation by 30% (rate ratio, 1.30 [CI, 1.16 to 1.46]). There was no evidence of difference in adverse event rate ratios (kidney stones: 1.17 [CI, 0.69 to 1.99]; hypercalcemia: 2.34 [CI, 0.83 to 6.66]; hypercalciuria : 1.65 [CI, 0.83 to 3.28]; death: 0.85 [CI, 0.31 to 2.36]). Limitations: Studies of people with prediabetes do not apply to the general population. The trials may not have been powered for safety outcomes. Conclusion: In adults with prediabetes, vitamin D was effective in reducing the risk of diabetes. Patients should weigh the benefits and harms of vitamin D supplementation with their doctor. |
Comments
A review of clinical trials found that higher vitamin D intake was associated with a 15 percent lower chance of developing type 2 diabetes in adults with prediabetes. The review is published in Annals of Internal Medicine .
Vitamin D is a fat-soluble vitamin available in or added to some foods, as a supplement, or produced by the body when ultraviolet rays from sunlight hit the skin. Vitamin D has many functions in the body, including a role in insulin secretion and glucose metabolism. Observational studies have found an association between having a low level of vitamin D in the blood and a high risk of developing diabetes.
Researchers at Tufts Medical Center conducted a systematic review and meta-analysis of three clinical trials comparing the impacts of vitamin D supplements on diabetes risk. The authors found that over a three-year follow-up period , new-onset diabetes occurred in 22.7 percent of adults who received vitamin D and 25 percent of those who received placebo, representing a reduction relative risk of 15 percent. According to the authors, extrapolating their findings to the more than 374 million adults worldwide who have prediabetes suggests that inexpensive vitamin D supplementation could delay the development of diabetes in more than 10 million people.
In an accompanying editorial , the authors from University College Dublin and the Food Safety Authority of Ireland, highlight that previous data have shown significant adverse effects for high vitamin D intake. They argue that professional societies that promote vitamin D therapy They have an obligation to advise doctors about the required intake of vitamin D and safe limits. They advise that this very high-dose vitamin D therapy could prevent type 2 diabetes in some patients, but it could also cause harm.
