Effect of Vitamin D Supplementation on Glycemic Control in Patients With Type 2 Diabetes (SUNNY Trial): A Randomized Placebo-Controlled Trial Diabetes Care 2015;38:1420–1426 | DOI: 10.2337/dc15-0323 OBJECTIVE Low vitamin D status has been associated with impaired glycemic control in patients with type 2 diabetes. The purpose of our study was to evaluate the ef- fect of vitamin D supplementation on glycemic control in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS This randomized, double-blind, placebo-controlled trial was conducted in 275 adult patients with type 2 diabetes without insulin treatment. Patients were randomly assigned to receive either vitamin D 3 (50,000 IU/month) or placebo for 6 months. To assess the primary outcome of the study, change in HbA 1c , we performed a linear regression analysis. RESULTS Mean baseline serum 25-hydroxyvitamin D [25(OH)D] increased from 60.6 6 23.3 to 101.4 6 27.6 nmol/L and 59.1 6 23.2 to 59.8 6 23.2 nmol/L in the vitamin D and placebo group, respectively. Mean baseline HbA 1c was 6.8 6 0.5% (51 6 6 mmol/mol) in both groups. After 6 months, no effect was seen on HbA 1c (mean difference: b = 0.4 [95% CI 20.6 to 1.5]; P = 0.42) and other indicators of glycemic control (HOMA of insulin resistance, fasting insulin, and glucose) in the entire study population. Subgroup anal- ysis in patients with a serum 25(OH)D <50 nmol/L or an HbA 1c level >7% (53 mmol/mol) did not differ the results. CONCLUSIONS In a well-controlled group of patients with type 2 diabetes, intermittent high-dose vitamin D supplementation did not improve glycemic control. Type 2 diabetes, characterized by peripheral insulin resistance and pancreatic b-cell dysfunction, represents a worldwide epidemic with significant comorbidity and mortality due to microvascular and macrovascular complications (1). Although therapies for type 2 diabetes have improved over the last few decades, new insights for the prevention and management of type 2 diabetes remain necessary due to the increased prevalence of the disease. 1 Department of Internal Medicine, Medical Cen- ter Alkmaar, Alkmaar, the Netherlands 2 Department of Clinical Chemistry, Medical Cen- ter Alkmaar, Alkmaar, the Netherlands 3 Amsterdam Rheumatology and Immunology Center, VU University Medical Center, Amsterdam, the Netherlands 4 Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, the Netherlands 5 Department of General Practice, DIAZON, Alkmaar, the Netherlands 6 Department of Internal Medicine/Endocrinology, VU University Medical Center, Amsterdam, the Netherlands Corresponding author: Suat Simsek, s.simsek@ mca.nl. Received 13 February 2015 and accepted 22 April 2015. Clinical trial reg. no. NTR3154, www.trialregister.nl. © 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. Yvonne H.M. Krul-Poel, 1 Sanne Westra, 1 Edwin ten Boekel, 2 Marieke M. ter Wee, 3 Natasja M. van Schoor, 4 Hans van Wijland, 5 Frank Stam, 1 Paul T.A.M. Lips, 6 and Suat Simsek 1,6 1420 Diabetes Care Volume 38, August 2015 CLIN CARE/EDUCATION/NUTRITION/PSYCHOSOCIAL