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Free serum 25-(OH)D levels similar among black, white women
Despite lower total serum 25-hydroxyvitamin D levels in black women, free serum 25-hydroxyvitamin D levels are similar across races, according to recent study findings published in The Journal of Clinical Endocrinology & Metabolism.
John Aloia, MD, and colleagues from Winthrop University Hospital in New York, evaluated 164 postmenopausal women who were equally divided by race and matched for age (mean age, 65 years) and BMI (mean BMI, 27.9 kg/m2) to determine the differences in total serum 25-(OH)D and free serum 25-(OH)D between the groups. Participants were measured for total 25-(OH)D, parathyroid hormone, 1,25-(OH)D, vitamin D binding protein (VDBP) and bone density. Enzyme-linked immunosorbent assay was used to measure free 25-(OH)D.
John Aloia
Black participants had lower total serum 25-(OH)D (19.59 ± 4.7 ng/mL) compared with white participants (26.93 ± 6.4 ng/mL; P < .0001), whereas levels of free 25-(OH)D were almost identical (black participants, 5.25 ± 1.24 pg/mL vs. white participants, 5.25 ± 1.27 pg/mL).
When using a monoclonal antibody, researchers found that black participants had lower VDBP (151.4 ± 73.2 µg/mL) compared with white participants (264.8 ± 95.5 µg/mL; P < .0001); however, this relationship was switched when using a polyclonal antibody (black participants, 438 ± 248 µg/mL vs. white participants, 369.9 ± 105.3 µg/mL; P < .01).
Compared with white participants, black participants had higher serum parathyroid hormone, 1,25-(OH)D and bone density.
“In conclusion, we report that although the total serum 25-(OH)D is lower in black than white Americans, free 25-(OH)D is almost identical,” the researchers wrote. “Their superior bone health alone should be sufficient to recognize that at the present time African Americans should not be subjected to targeted screening for ‘low’ total serum 25-(OH)D. The finding of almost identical free 25-(OH)D between races confirms the lack of justification for such screening.”
However, the researchers said the findings do not suggest free 25-(OH)D levels are a better biomarkers for vitamin D status compared with total 25-(OH)D.
“Moreover, a case could be made for use of free 25-(OH)D when vitamin D status is examined in cirrhosis, pregnancy and other changes in protein binding,” the researchers wrote. “The appropriateness of using free 25-(OH)D to assess vitamin D status in African Americans merits further study.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.