Anastassios G. Pittas, M.D MS Professor Co-Director, Diabetes and Lipid Center; Tufts University School of Medicine

The Vitamin D and Type 2 Diabetes Study Interview with:

Anastassios G. Pittas, M.D MS Professor Co-Director, Diabetes and Lipid Center; Tufts University School of Medicine

Dr. Pittas

Anastassios G. Pittas, M.D MS
Co-Director, Diabetes and Lipid Center;
Tufts Medical Center What is the background for this study? What are the main findings?

Response: Observational studies have consistently reported an association between low blood vitamin D level and development of type 2 diabetes. However, whether vitamin D supplementation lowers risk of developing diabetes is not known. We designed and conducted the Vitamin D and diabetes (D2d) study to answer this question.  We randomized 2,423 people with prediabetes to 4,000 IU/day of vitamin D3 or placebo and followed them for new-onset diabetes with blood tests every 6 months for an average of 2.5 years. About 80% of participants had sufficient vitamin D level at baseline (25-hydroxyvitamin D level >= 20 ng/mL). The trial was designed to show a reduction of 25% or more in diabetes risk with vitamin D.

The study was unable to show a reduction of 25% or more. At the end of the study, there was a 12% reduction in risk of developing diabetes with vitamin D, which missed statistical significance (hazard ration 0.88; 95% confidence interval 0.75 to 1.04). In a small subgroup of participants with vitamin D deficiency at baseline (25-hydroxyvitamin D level < 12 ng/mL) there was 62% reduction in risk of diabetes with vitamin D (hazard ration 0.38; 95% confidence interval 0.18 to 0.80). What should readers take away from your report?

Response: The D2d study was one piece of the vitamin D and type 2 diabetes puzzle. Our overall results are consistent with two other trials (one in Norway and one in Japan) which also showed a remarkably similar reduction in diabetes risk (10-13%) in the entire study population. When considered together with the other two similar (but smaller) trials, vitamin D may have a 10-15% reduction in risk of diabetes among people at risk for type 2 diabetes not selected for vitamin D insufficiency; however, none of the trials were large enough to show this effect size. In the D2d study, the effect of vitamin D was more pronounced among those with vitamin D deficiency at baseline, which is consistent with the concept that the effect of nutrients depends on nutrient status at baseline. What recommendations do you have for future research as a result of this work? 

Response: We are currently examining the effect of vitamin D on insulin secretion and insulin sensitivity in the D2d study. We also plan to combine data from the other two trials to learn more about the effect of vitamin D on diabetes risk, specifically whether there are specific thresholds of vitamin D status that are relevant to diabetes risk. 

I have no disclosures. The study was funded by NIH and ADA. 


The Vitamin D and Type 2 Diabetes (D2d) Study—A Multicenter Randomized Controlled Trial for Diabetes Prevention 

Anastassios G. Pittas, M.D., Bess Dawson-Hughes, M.D., Patricia Sheehan, R.N., M.P.H., M.S., James H. Ware, Ph.D., William C. Knowler, M.D., Dr.P.H., Vanita R. Aroda, M.D., Irwin Brodsky, M.D., Lisa Ceglia, M.D., Chhavi Chadha, M.D., Ranee Chatterjee, M.D., M.P.H., Cyrus Desouza, M.B., B.S., Rowena Dolor, M.D.,  et al.,for the D2d Research Group*

June 7, 2019
DOI: 10.1056/NEJMoa1900906

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Last Updated on June 10, 2019 by Marie Benz MD FAAD