American Diabetes Association

Conference summaries


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

Presented by: Anastassios G. Pittas, MD
Tufts Medical Center, Boston MA, USA
Erin S. LeBlanc, MD, MPH
Kaiser Permanente, Portland, OR, USA
Myrlene Staten, MD
National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, US
for the D2d Research Group
  • Vitamin D is a hormone with multiple actions throughout the body, with the primary function of promoting optimal bone and mineral metabolism.
  • The D2d study aims to provide important information on the role of vitamin D in prevention of type 2 diabetes.
  • The results from this study could have major implications for public health.

Vitamin D is crucial for skeletal health, and its potential benefits on many other health outcomes have been widely studied. Observational studies have suggested that vitamin D may reduce the risk of progression from prediabetes to type 2 diabetes. Vitamin D supplementation has also been shown to have benefits on function of pancreatic beta cells. However, the role of vitamin D supplementation in lowering the risk of diabetes onset has not been examined in a well-designed randomized trial.

  • The multicenter D2d trial investigated whether oral daily vitamin D supplementation can delay the onset of type 2 diabetes among people with prediabetes.

Type of study, patients, and inclusion criteria

  • D2d randomized participants to daily placebo or vitamin D supplementation (4,000 IU).
  • Participants had to meet at least two of three glycemic criteria for prediabetes (impaired fasting glucose level, impaired glucose tolerance, and HbA1c of 5.7 to 6.4%).
  • Participants were asked to refrain from using diabetes-specific or weight-loss medications during the trial and to limit the use of outside-of-trial vitamin D to 1000 IU per day from all supplements, including multivitamins.

Patient population

  • Total number of enrollees: 2,423.
  • Placebo: 1,212.
  • Vitamin D supplementation: 1,211.

Primary outcome measure

  • The primary outcome in this time-to-event analysis was new-onset diabetes.
  • The trial design was event-driven, with a target number of diabetes case onset of 508.

Main findings of D2d

  • By month 24, mean serum 25-hydroxyvitamin D in the vitamin D supplemented group was 54.3 ng/mL (27.7 ng/mL at baseline) vs. 28.8 ng/mL for the placebo group (28.2 ng/mL at baseline).
  • After a median follow-up of 2.5 years, new-onset diabetes occurred in 293 participants in the vitamin D supplemented group and 323 in the placebo group (9.39 and 10.66 events per 100 person-years, respectively).
  • The hazard ratio for vitamin D compared with placebo was 0.88 (95% CI, 0.75 to 1.04; P=0.12) (Figure).
  • The incidence of adverse events was not significantly different between groups.
  • Among people at high risk for type 2 diabetes and not selected for vitamin D insufficiency, oral supplementation with vitamin D at 4,000 IU/day was not associated with a significantly lower risk of diabetes compared to placebo.

Key Messages/Clinical Perspectives

  • Vitamin D does not appear to have a significant effect on the risk of new-onset diabetes in people with prediabetes, although the observed hazard ratio of 0.88 suggests the possibility of a modest benefit of vitamin D supplementation.

Trial: NCT01942694



  1. Pittas AG, Dawson-Hughes MC, Sheenan P, et al. Vitamin D Supplementation and Prevention of Type 2 Diabetes. N Engl J Med. 2019 Jun 7. [Epub ahead of print].

Present disclosure: The presenters has reported that no relationships exist relevant to the contents of this presentation.

Written by: Patrick Moore, PhD

Reviewed by: Marco Gallo, MD

All report

Welcome to the ADA 2019 Highlights

Jose C. Florez, MD, PhD
Chair, ADA Scientific Sessions Meeting Planning Committee
The 79th American Diabetes Association’s Scientific Sessions were held in San Francisco, California from June 7-11, 2019. The meeting was attended by over 15,000 professional attendees from 115 countries, … [ Read all ]



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

Presented by: Anastassios G. Pittas, MD; Erin S. LeBlanc, MD, MPH; Myrlene Staten, MD; for the D2d Research Group


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Oral Semaglutide—The PIONEER Program Trials

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ADA Nutrition Therapy for Adults with Diabetes—2019 Consensus Report

Presented by: Alison B. Evert, MD; Janice MacLeod, MA, RDN, CDE; William S. Yancy, Jr., MD, MHS; W. Timothy Garvey, MD; Ka Hei Karen Lau, MS, RD, LDN, CDE; Christopher D. Gardner, PhD; Kelly M. Rawlings, MS



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Presented by: Julie A. Lovshin, MD, PhD; Jens J. Holst, MD, DMSc; David C. Wheeler, MD


Nonalcoholic Fatty Liver Disease (NAFLD) and Nonalcoholic Steatohepatitis (NASH)—The Overlooked Complications of Type 2 Diabetes

Presented by: Elisabetta Bugianesi, MD, PhD; Zobair Younossi, MD, MPH; Kenneth Cusi, MD


Controversies in the Evaluation and Management of Dyslipidemia in Patients with Diabetes

Presented by: Amy Sanghavi Shah, MD, MS; Dan Streja, MD; Savitha Subramanian, MD; Lisa Tannock, MD


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Presented by: Kamlesh Khunti, MD, PhD, FRCGP, FRCP; Elizabeth Selvin, PhD, MPH; Frans Pouwer, PhD; Sophia Zoungas, MBBS (Hons), PhD, FRACP