Vitamin D plays an important part in the human immune response and deficiency can leave individuals less able to fight infections like HIV-1. Now an international team of researchers has found that high-dose vitamin D supplementation can reverse the deficiency and also improve immune response. "Vitamin D may be a simple, cost-effective intervention, particularly in resource-poor settings, to reduce HIV-1 risk and disease progression," the researchers report in today's (June 15) online issue of Proceedings of the National Academy of Sciences.

The researchers looked at two ethnic groups in Cape Town, South Africa, to see how seasonal differences in exposure to ultraviolet B radiation, dietary vitamin D, genetics, and pigmentation affected vitamin D levels, and whether high-dose supplementation improved deficiencies and the cell's ability to repel HIV-1.

"Cape Town, South Africa, has a seasonal ultraviolet B regime and one of the world's highest rates of HIV-1 infection, peaking in young adults, making it an appropriate location for a longitudinal study like this one," said Nina Jablonski, Evan Pugh Professor of Anthropology, Penn State, who led the research.

One hundred healthy young individuals divided between those of Xhosa ancestry -- whose ancestors migrated from closer to the equator into the Cape area -- and those self-identified as having Cape Mixed ancestry -- a complex admixture of Xhosa, Khoisan, European, South Asian and Indonesian populations -- were recruited for this study. The groups were matched for age and smoking. The Xhosa, whose ancestors came from a place with more ultraviolet B radiation, have the darkest skin pigmentation, while the Khoisan -- the original inhabitants of the Cape -- have adapted to the seasonally changing ultraviolet radiation in the area and are lighter skinned. The Cape Mixed population falls between the Xhosa and Khoisan in skin pigmentation levels.