Big doses needed for elimination of low vitamin D levels for African Americans: Study

18-Jul-2012 - Last updated on 19-Jul-2012 at 14:52 GMT

“It is important to point out the absence of any significant toxicity of the vitamin D3 intervention used in this clinical study” - Garrett-Mayer et al.

Over 90% of African Americans may have vitamin D deficiency, and daily doses of 4,000IU may be needed to eliminate deficiency, says a new study from the Medical University of South Carolina.

One year of supplementation with 4,000IU of vitamin D3 was found to eliminate any differences in blood levels of the vitamin between African American and white men, according to results published in the American Journal of Clinical Nutrition.

“The results of this interventional study show the feasibility and efficacy of this approach in eliminating hypovitaminosis D, which is a crucial health disparity among African Americans,” wrote researchers led by Elizabeth Garrett-Mayer.

“Vitamin D3–based interventions targeting adult African Americans could have a beneficial impact on the current epidemics of cardiometabolic disorders in this underserved population, would provide strong evidence for the causal role played by vitamin D deficiency in these pathologies, and could help eliminate well-documented health disparities.”

Sunshine vitamin

Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.

Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.

While our bodies do manufacture vitamin D on exposure to sunshine (UV-B radiation with a wavelength between 290 and 315 nm), the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.

In addition, darker skin is known to limit a person’s ability to produce vitamin D, and various surveys have reported that as much as 90% of African Americans may be vitamin D deficient, defined as having 25(OH)D levels below 30 ng/mL.

Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.

Study details

Garrett-Mayer and her co-workers recruited 47 African American and white men with an average age of 64 to participate in their study. All participants received a daily vitamin D3 dose of 4,000 IU for one year. Supplements were manufactured by JR Carlson Laboratories Inc.

Results showed that, at the start of the study, over 90% of African Americans had deficient levels of 25(OH)D and about 66% had very low levels (below 20 ng/mL). There were also “significant disparities” in vitamin D levels between the African American men and the white men.

“Supplementation with 4000 IU/d for 1 year eliminated any significant differences in circulating concentrations of 25(OH)D between African American and white men,” wrote the researchers.

Challenging IoM conclusions

“It is important to point out the absence of any significant toxicity of the vitamin D3 intervention used in this clinical study,” they wrote.

“The Endocrine Society Practice Guidelines, compared with those of the Food and Nutritional Board of the Institute of Medicine, recommend a 2- to 3-fold increase in vitamin D3 intake, with a tolerable upper intake level of 10,000 IU/d,” they explained.

“The Institute of Medicine report also concluded that circulating 25(OH)D concentrations were unrelated to various neoplasias, and in fact higher concentrations of circulating 25(OH)D could make the cancer worse.

“These conclusions of the Institute of Medicine report are not supported by our current data.”

Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.112.034256
“Vitamin D3 supplementation (4000 IU/d for 1 y) eliminates differences in circulating 25-hydroxyvitamin D between African American and white men”
Authors: E. Garrett-Mayer, C.L. Wagner, B.W. Hollis, M.S. Kindy, S. Gattoni-Celli