African-American men living in low sunlight areas are more likely to experience vitamin D deficiency than European-American men living in the same environment. Researchers believe that these findings should change recommendations for daily intake¹ of vitamin D. "This study shows that across the board vitamin D recommendations just won't work for everybody," said Adam B. Murphy, M.D., M.B.A., clinical instructor² in the department of urology（泌尿学） at Northwestern University Feinberg School of Medicine, who reported the study at the Fourth AACR Conference on The Science of Cancer Health Disparities, held Sept. 18-21, 2011, in Washington, D.C.

 

"With so many diseases linked to low levels of vitamin D, we should have more stratified（分层的） recommendations to consider groups within the population instead of making monolithic³（整体的） suggestions," he added.

 

Researchers evaluated the marker for vitamin D -- the 25 hydroxyvitamin D level (25-OH D level) -- in 492 men aged⁴ 40 to 79 years who lived in Chicago, a low ultraviolet radiation (UVR) part of the country. Of that group, 93 percent of African-American men and 69.7 percent of European-American men were vitamin D deficient⁵; having 25-OH D levels of less than 30 ng/mL.

 

Results showed that vitamin D levels were low in African American men, those with lower income and those with higher body mass index. Low sunlight exposure is a known factor in lower levels of vitamin D, but researchers found that African American men still had lower levels of vitamin D in sunnier seasons.

 

Murphy attributes low vitamin D levels to the composition of African-American skin, which contains more of the pigment⁶ melanin（黑色素） than lighter⁷ skin. When UVR light hits the skin cells, it reacts with the molecule⁸ 7-dehydrocholesterol to begin the production of vitamin D, which is then further processed by the body to make active vitamin D. In African-Americans, though, melanin blocks UVR rays from being absorbed, thus reducing the amount of vitamin D naturally produced.

 

Vitamin D deficiency has been linked to multiple diseases, including breast cancer, prostate cancer, diabetes⁹, rheumatoid arthritis¹⁰（风湿性关节炎） and multiple sclerosis, which is why Murphy believes it is essential to adjust recommendations to reflect differences between African Americans and European-Americans.

 

"Because we have a lot of special populations in the United States -- people who have darker skin, people who cover their skin for religious reasons and people who live in poor sunlight environments -- there shouldn't be uniform vitamin D recommendations for the entire population," he said.

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