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N Engl J Med. 2019 Aug 8;381(6):520-530. doi: 10.1056/NEJMoa1900906. Epub 2019 Jun 7.

Vitamin D Supplementation and Prevention of Type 2 Diabetes.

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From Tufts Medical Center (A.G.P., L.C., P.F., J.N., E.M.V.), the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (B.D.-H.), Brigham and Women's Hospital (V.R.A.), and Harvard School of Public Health (J.H.W.), Boston, and the Spaulding Rehabilitation Network, Charlestown (P.S.) - all in Massachusetts; National Institute of Diabetes and Digestive and Kidney Diseases, Phoenix, AZ (W.C.K.); the Maine Medical Center (I.B.) and the Maine Medical Center Research Institute (C.R.) - both in Scarborough; HealthPartners Institute, Minneapolis (C.C.); Duke University Medical Center, Durham, NC (R.C., R.D.); the University of Nebraska Medical Center and Omaha Veterans Affairs Medical Center, Omaha (C.D.); Baylor College of Medicine, Houston (J.F.), and the University of Texas Southwestern Medical Center, Dallas (P.R.) - both in Texas; MedStar Good Samaritan Hospital, Baltimore (A.G.), MedStar Health Research Institute, Hyattsville (J.P.), and the National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda (M.S.) - all in Maryland; Pennington Biomedical Research Center, Baton Rouge, LA (D.S.H.); the University of Tennessee Health Science Center, Memphis (K.C.J.); Cleveland Clinic, Cleveland (S.R.K.); Stanford University Medical Center, Stanford (S.K.), and the Keck School of Medicine of the University of Southern California, Los Angeles (A.P.) - both in California; Kaiser Permanente Center for Health Research-Northwest, Portland, OR (E.S.L.); the University of Vermont, Burlington (M.R.L.); Northwell Health Lenox Hill Hospital, New York (E.L.); Northwestern University, Chicago (L.M.N.); the Medical University of South Carolina, Charleston (P.O.); Emory University School of Medicine, Atlanta, and the Atlanta Veterans Affairs Medical Center, Decatur - both in Georgia (L.S.P.); AdventHealth Translational Research Institute for Metabolism and Diabetes, Orlando, FL (R.P.); the University of Colorado Denver and the Veterans Affairs Eastern Colorado Health Care System, Denver (N.R.); and the University of Kansas Medical Center, Kansas City (D.R.).



Observational studies support an association between a low blood 25-hydroxyvitamin D level and the risk of type 2 diabetes. However, whether vitamin D supplementation lowers the risk of diabetes is unknown.


We randomly assigned adults who met at least two of three glycemic criteria for prediabetes (fasting plasma glucose level, 100 to 125 mg per deciliter; plasma glucose level 2 hours after a 75-g oral glucose load, 140 to 199 mg per deciliter; and glycated hemoglobin level, 5.7 to 6.4%) and no diagnostic criteria for diabetes to receive 4000 IU per day of vitamin D3 or placebo, regardless of the baseline serum 25-hydroxyvitamin D level. The primary outcome in this time-to-event analysis was new-onset diabetes, and the trial design was event-driven, with a target number of diabetes events of 508.


A total of 2423 participants underwent randomization (1211 to the vitamin D group and 1212 to the placebo group). By month 24, the mean serum 25-hydroxyvitamin D level in the vitamin D group was 54.3 ng per milliliter (from 27.7 ng per milliliter at baseline), as compared with 28.8 ng per milliliter in the placebo group (from 28.2 ng per milliliter at baseline). After a median follow-up of 2.5 years, the primary outcome of diabetes occurred in 293 participants in the vitamin D group and 323 in the placebo group (9.39 and 10.66 events per 100 person-years, respectively). The hazard ratio for vitamin D as compared with placebo was 0.88 (95% confidence interval, 0.75 to 1.04; P = 0.12). The incidence of adverse events did not differ significantly between the two groups.


Among persons at high risk for type 2 diabetes not selected for vitamin D insufficiency, vitamin D3 supplementation at a dose of 4000 IU per day did not result in a significantly lower risk of diabetes than placebo. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and others; D2d number, NCT01942694.).

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