While doctors routinely perform vitamin D blood tests during annual physicals, many of the 70 to 90 percent of African-Americans who are diagnosed as vitamin D deficient may actually have healthy levels of the vitamin and could be taking supplements unnecessarily.
That’s the conclusion of a new study from Massachusetts General Hospital, which found that tests to measure total vitamin D levels don’t reflect the genetic differences that lead some people — often African-Americans and Asians from warmer climates — to carry more of the “free” form of the nutrient. This free vitamin D — which is really a hormone — is readily available for the body to use to maintain strong bones and other cellular functions.
In the study, published last Wednesday in the New England Journal of Medicine, researchers from MGH and the National Institutes of Health measured vitamin D levels in more than 2,000 African-Americans and Caucasians ages 30 to 64 living in Baltimore. Their research found that African-Americans tended to have lower levels of vitamin D and less vitamin D–binding protein when compared with Caucasians, which was linked to a gene mutation. African-Americans also had denser bones and higher levels of calcium.
“We shouldn’t be calling people with low vitamin D levels ‘deficient’ if they have strong bones and significant amounts of free [vitamin] D hormone,” said study senior author Dr. Ravi Thadhani, chief of nephrology at Mass. General.