Why is HIV so prevalent in Africa?

Despite the fact that there are millions of people around the world suffering from it, HIV is actually surprisingly hard to transmit. Each time a man has unprotected sex with an HIV-positive man, his risk of becoming infected is only 82 in 10,000, and the risk is even lower for heterosexual sex: a woman only has a 9 in 10,000 chance of contracting the virus from an HIV-positive male during an unprotected sexual encounter. Researchers have long wondered why this is, and whether our bodies have some kind of preliminary line of defense against the virus.

Some scientists have cited the low HIV transmission rates yet high prevalence rates as evidence that the world, and especially Africa, is chock full of extremely promiscuous people. But a study published in the Lancet last year suggests that's not the case: single men and women in Africa actually report being less sexually active than their counterparts in developed countries. Of course, third world citizens are also less likely to use condoms, but even so, the evidence does not support the idea that Africa is extraordinarily promiscuous.

Why, then, is HIV such a huge problem there? Could Africans lack a first-line defense mechanism that people in other countries have?

Enter Harold Foster, a geographer at the University of Victoria in Canada who studies the causes of chronic disease. Publishing in the journal Medical Hypotheses, Foster suggests that the reason some populations are better able to fight off HIV has to do with an antioxidant called selenium, an element that is toxic in large doses but necessary at low doses for proper cell function. In countries in which HIV prevalence is the highest, such as Zaire, Uganda, Tanzania, Kenya and South Africa, soil selenium levels are the lowest; however, in Senegal, where there is widespread unprotected promiscuity but low HIV prevalence, selenium levels are high. This trend is not limited to Africa, either, says Foster. HIV rates are abnormally low in Bolivia, where selenium exportation is common; and, although selenium deficiency is common in Scandinavia, HIV infection rates are surprisingly low in Finland, where selenium has been added to fertilizers since 1984.

But why selenium? According to a 1990 study, the trace element is key to the proper functioning of the immune system. Other studies published in the journal Biological Trace Element Research suggest that selenium protects against Hepatitis B and C as well. So does this mean that we should ship mass quantities of selenium into countries with selenium-deficient soil? Well, that might be a little bit premature, because Foster's theory is purely speculative; no research evidence directly supports it. But his idea is certainly thought-provoking, and it seems to warrant further study -- especially given the fact that a whopping 36 million people suffer from HIV around the globe.