Measuring vitamin D binding protein (VDBP) may be important for accurately determining vitamin D deficiency, especially among African Americans, reports a team of researchers led by the National Institute on Aging, NIH, in the November 21, 2013 issue of the New England Journal of Medicine.
Vitamin D deficiency is more commonly diagnosed among African Americans than in white Americans. However, the poor skeletal-bone health associated with vitamin D deficiency is less common in this population—African Americans generally have higher bone density and lower risk for fragility fractures than white Americans. This suggests that the vitamin D deficiency as it is currently diagnosed is likely inaccurate. With this study, researchers were able to evaluate the potential role of VDBP, the protein that carries vitamin D throughout the body, in assessing clinically significant vitamin D deficiency.
The team measured levels of vitamin D, calcium, and VDBP, as well as bone density, and analyzed the genetic form of (genotyped) VDBP in NIA’s Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) cohort, a study comprised of community-dwelling blacks and whites initially aged 30 to 64 residing in Baltimore, Maryland. They found that, compared to whites, African Americans had lower levels of vitamin D and VDBP, but higher bone density and higher levels of calcium, another micronutrient important to bone health. Genetic analysis of participants’ VDBP indicated that African Americans were more likely to have one form of the protein and whites another. The version of VDBP more prevalent in African Americans, but also seen in some white participants, was associated with lower levels of the binding protein and lower levels of vitamin D.
Researchers suggest that low VDBP may have a protective effect against the symptoms typically associated with lower vitamin D levels and clinically relevant vitamin D deficiency. Therefore, rather than diagnosing and treating vitamin D deficiency based on only lower vitamin D levels, clinicians may also want to account for VDBP in their assessment, especially in African Americans. Routine Vitamin D supplementation should be carefully considered in the context of the finding of this study.
Reference “Vitamin D Binding Protein and Vitamin D Status of Community Dwelling Black and White Americans” by Powe, C.E., Evans, M.K., et al. New England Journal of Medicine. DOI: 10.1056/NEJMoa1306357 (November 21, 2013).