The absorption and metabolism of vitamin D is comparable among Caucasian and African American women, according to new research published in the Journal of Clinical Endocrinology & Metabolism.
There is a well known disparity gap in vitamin D levels between different ethnicities. For example, in a CDC report last year, 65% of African Americans were deficient in vitamin D compared to just 20% of Caucasians. While it is presumed that skin color plays the largest and perhaps sole hand in this gap (the darker the skin, the more sun exposure needed to make vitamin D), researchers still wanted to know, might different ethnicities absorb or metabolize vitamin D differently?
If so, there would be big implications in setting recommended daily allowances in the future.
In this study, Professor J Christopher Gallagher, MD, from Creighton University School of Medicine in Omaha, Nebraska, and colleagues investigated this topic.
They measured vitamin D levels in 110 post-menopausal African American women aged 57-90 with vitamin D levels of 20 ng/ml or less. The women were randomized to receive a placebo or vitamin D supplement at 1 of 8 dose levels, ranging from 400 IU to 4,800 IU, for 1 year.
The authors compared the results of the present study with a parallel study examining vitamin D metabolism in Caucasian women. Vitamin D status at baseline was lower in the African American participants compared to the Caucasian participants (13 ng/ml vs 17 ng/ml respectively). They found that the increase in serum vitamin D after supplementation in African American women was similar to that seen in the Caucasian women.
Furthermore, 97.5% of women on 800 IU/daily – the RDA set by the IOM for elderly – from both the African American and Caucasian groups reached a level of 20 ng/ml.
The researchers did not report what dose it took for the African American women to reach a level of 30 ng/ml and how that compared to the Caucasian women. It is reasonable to assume that since African Americans had lower baseline levels, that they would need a bigger dose than Caucasian women to ensure 97.5% of the population reached a 30 ng/ml threshold.
However, for the time being, it looks as though vitamin D is absorbed and metabolized the same in both Caucasians and African Americans.
The authors conclude,
“The implication therefore is that the absorption and metabolism of vitamin D are similar in African American and Caucasian women. Although serum levels of serum 25OHD are usually much lower in African Americans, it is most likely because of decreased formation of vitamin D in skin.”