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Research that shows how a lack of vitamin D can increase people's susceptibility to tuberculosis (TB) could explain why people in Africa and other parts of the developing world are particularly prone to the disease.

The findings, published yesterday (23 February) by Science, suggest that vitamin D supplements could be used to fight the disease. TB kills two million people a year, mostly in developing countries.

The study shows that a successful immune response to TB depends on the conversion of vitamin D into a hormone that white blood cells use to kill the invading bacteria.

Although foods such as milk and salmon contain the vitamin, larger amounts are produced in people's skin after exposure to sunlight. However, the darker their skin is, the less vitamin D they produce.

The researchers, led by Robert Modlin of the University of California at Los Angeles, United States, found that African-Americans also had less of the vitamin's active form in their blood than white Americans.

Co-author John Adams of the Cedars-Sinai Medical Center, also in Los Angeles, told SciDev.Net that there have been no large-scale studies of the prevalence of vitamin D deficiency. However, smaller studies suggest the problem is widespread among poor populations throughout Africa, the Middle East and South Asia.

"A study in Tunisia found that nearly half the study population had vitamin D levels well below the threshold for D deficiency," said Adams. "Similar results were found on the Indian subcontinent."

Adams added: "People with low levels of vitamin D are more likely to succumb to TB. This could be corrected simply by using supplements to return their vitamin D levels to normal."

But Robert Wilkinson, a TB specialist at the University of Cape Town, South Africa, says more research, including human trials, is needed before we can be certain of the effect that supplying vitamin supplements on a large-scale would have on the disease.

Read the full article in Science

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