Effects of Vitamin D Supplementation in Older African American Women

DermatologistsBlog.com Author Interview: Dr J. C. Gallagher, MD

Bone Metabolism Unit, Creighton University School of Medicine,
601 North 30th Street, Suite 6718, Omaha, Nebraska 68131

DermatologistsBlog.com: What are the main findings of the study?

Dr J. C. Gallagher: The main findings are that baseline serum 25OHD levels are lower in African Americans compared to Caucasians.

In a dose ranging controlled study the increase in serum 25OHD after 5 different doses of vitamin D (400-4800IU daily) was the same in both groups at 6 and after 12 months.

In both groups 800 IU daily exceeded a serum 25OHD level of 20ng/ml –in keeping with the IOM recommendations 2012.

Thus the absorption and metabolism of vitamin D must be the same in both ethnic groups.

Since dietary vitamin D is the same in both groups then by inference the lower levels of 25OHD in African Americans must be due to decreased formation of D in the skin since skin produces more than 80 percent of the vitamin D input into the body.

DermatologistsBlog.com: Where any of the findings unexpected?

Dr J. C. Gallagher: Unexpected findings included:

That 25OHD is quite tightly regulated and that at an intake of 3000-4000 IU /daily serum 25OHD reaches a plateau at about 40ng/ml (100nmol/L)

The latest results suggests that regulation of 25OHD is due to 24 hydroxylation of 25OHD into the inactive metabolite 24,25 dihydroxyvitamin D instead of the active metabolite 1,25 dihydroxyvitamin D and this may be the primary mechanism to avoid vitamin D intoxication.

DermatologistsBlog.com: What recommendations do you have from the study?

Present recommendation for clinical is conservative.

Increase vitamin D intake to 400 IU daily in African Americans

Increase vitamin D intake to 800 IU daily in  Caucasians

 -This is based on osteoporosis studies that show an increase in fractures in African Americans when serum 25OHD increases above 20ng/ml whereas in Caucasians there is a decrease in fractures.

Citation:

Effects of Vitamin D Supplementation in Older African American Women
J. Christopher Gallagher, Munro Peacock, Vinod Yalamanchili and Lynette M. Smith
Published online before print February 5, 2013, doi: 10.1210/jc.2012-3106
The Journal of Clinical Endocrinology & Metabolism February 5, 2013 jc.2012-3106