People on a regimen containing efavirenz (Sustiva or Atripla) had a higher risk of having low vitamin D levels—which can lead to bone problems—than people on a protease inhibitor regimen. The study, which also found race and season of the year to play a role in vitamin D levels, was presented at the Fifth International AIDS Society (IAS) Conference on HIV Pathogenesis, Treatment and Prevention in Cape Town.

A number of recent studies have found abnormally low vitamin D levels in people with HIV. Researchers are concerned about this because low vitamin D is clearly linked to loss of bone density in both HIV-positive and HIV-negative people—and low bone density can lead to fractures, which in turn increase the risk of further illness.

Our primary source of vitamin D is exposure to the sun. For people in northern latitudes, getting enough sunlight during the cold, dark northern winters can be a challenge.

To determine the factors associated with low vitamin D levels, Tanya Welz, MRCP, MPH, and her colleagues from Kings College in London examined the medical records and blood test results of 1,041 HIV-positive people being treated in their clinic.

Welz’s team found that low vitamin D levels were nearly universal in their cohort of patients, but that certain groups were much more likely to have very low levels. Those with very low vitamin D levels included black patients, patients whose levels were tested during the winter, and patients currently taking efavirenz.

The authors conclude that further studies are needed to illustrate the mechanism by which efavirenz or other antiretrovirals contribute to bone loss.