Building on previously established benchmarks that the risk of diabetes is higher when the levels of 25-hydroxyvitamin D [25(OH)D] levels are lower among non-Hispanic white individuals, a team from the Division of Endocrinology, Diabetes and Metabolism at Ohio State University in Columbus and colleagues explored the less clear association between diabetes and vitamin D among African American (AA) populations and published their findings in Nutrition & Diabetes.
Lead author Joshua J. Joseph, an endocrinologist and an assistant professor in the Division of Endocrinology, Diabetes and Metabolism at Ohio State, and colleagues explored the association of serum 25(OH)D with incident diabetes among AAs and stratified the study group by detectable 25(OH)D2. And although 25(OH)D2 represents a smaller percentage of total 25(OH)D, it binds the human vitamin D–binding protein less potently than 25(OH)D3 and is thus thought to be more biologically active.
The team collected serum 25(OH)D2 and 25(OH)D3 from AA participants in the Jackson Heart Study from 2000 to 2004, and using a cosinor model, they adjusted for the seasonality of 25(OH)D3. They then combined 25(OH)D3 and 25(OH)D2 to determine total 25(OH)D. Criteria including fasting glucose samples that were 126 mg/dL or greater, glycosylated hemoglobin A1C 6.5% or greater, or if the subjects reported use of medication for the treatment of diabetes were assessed over 12 years among adults without diabetes at baseline. Hazard ratios (HR) were estimated using Cox modeling, and adjustments were made for sex, age, occupation, education, smoking status, alcohol use, levels of physical activity, aldosterone, and BMI.
The researchers reported that among the 3,311 adults (63% female and with a mean age of 53.3 years), 584 participants developed diabetes over a median of 7.7 years after the aforementioned adjustments. In terms of lower risk of diabetes, levels of 25(OH)D 20 ng/mL or greater compared with less than 12 ng/mL were associated with an HR 0.78 (95% CI: 0.61, 1.00). Among subjects with detectable 25(OH)D2 and 25(OH)D3 (n = 1,671), levels of 25(OH)D 20 ng/mL or greater compared with less than 12 ng/mL were associated with a 35% (HR 0.65; 95% CI: 0.46, 0.91) lower risk.
Reinforcing the importance of their work, coauthor Amaris Williams, a postdoctoral scholar in the Division of Endocrinology, Diabetes and Metabolism at Ohio State, commented, “It’s been known for some time that low levels of vitamin D in the blood—measured as 25(OH)D—are associated with an increased risk of diabetes in White populations, but our research strongly suggests that this relationship also holds true for African Americans.” She stated further, “Our MESA-study findings suggest that the inverse association between 25(OH)D and the risk of developing diabetes is similar across races and ethnicities.”
Dr. Joseph concluded, “Our studies suggest that higher levels of vitamin D in African Americans may protect against the development of diabetes.” He further elaborated, “More research is needed to learn whether vitamin D supplementation among individuals with vitamin D deficiency can improve risk for diabetes.”
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