December 4, 2013
Tests Often Misdiagnosis Black Americans as
Vitamin D Deficient

Boston—Based on widely used tests, an alarming percentage of black Americans are vitamin D deficient. Yet, they often do not present with low bone density and increased fracture risk, which are common symptoms of the problem.

Trying to solve the conundrum, researchers from several Boston medical facilities found that the common test may not be measuring the correct form of Vitamin D for the specific population. Their results were published recently in the New England Journal of Medicine.

The researchers found that genetic differences in a D-binding protein may explain the discrepancy between the prevalence of vitamin D deficiency in symptom-free black Americans, diagnosed by measuring the molecule 25-hydroxyvitamin D (25OHD).

Measurement of 25OHD alone consistently classifies from 70% to 90% of black Americans as vitamin D deficient. Yet, the researchers note, symptoms such as low bone density and increased fracture risk are actually less prevalent among black patients.

For the study, investigators examined data from more than 2,000 participants in HANDLS—Healthy Aging in Neighborhoods of Diversity Across the Life Span—a large National Institutes of Health (NIH)–sponsored study of age-associated health disparities in socioeconomically diverse black and white individuals in Baltimore. HANDLS participants, ranging in age from 30 to 64, were interviewed and received medical examinations between 2004 and 2009.

Boston researchers analyzed levels of 25OHD, levels and genetic variants of D-binding protein, and levels of calcium and parathyroid hormone along with bone density readings in about 1,200 white and 900 black participants.

Results found significantly lower levels of both 25OHD and D-binding protein in black participants, compared with white participants, with genetic variation explaining the difference in about 80% of cases. Black participants had significantly higher bone density and calcium levels, however.

“Black people are frequently treated for vitamin D deficiency, but we may not be measuring the right form of vitamin D to make that diagnosis," said lead researcher Ravi Thadhani, MD, MPH, of Massachusetts General Hospital and Harvard Medical School. “While our finding that 80% of black participants in this study met criteria for vitamin D deficiency is consistent with previous studies, we were surprised to find no evidence of problems with bone health. Most vitamin D in the bloodstream is tightly bound to D-binding protein and is not active. When we determined the concentrations of circulating non-bound vitamin D, which would be available to cells, we found that levels of this form were equivalent between black and white participants, which suggested to us that these black individuals may not be truly deficient."

Thadhani pointed out that no commercially available assays directly measure bioavailable levels of 25OHD, even though those tests likely “would more accurately identify those with true vitamin D deficiency, allowing us to direct treatment toward those who really need it. Additional studies need to be conducted to establish optimal levels of bioavailable 25ODH across all racial and ethnic groups."

U.S. Pharmacist Social Connect