Up to 52 percent of people with HIV in a Swiss study had dangerously low vitamin D levels. The study, published in the May 15 issue of AIDS, also found that people taking non-nucleoside reverse transcriptase inhibitors (NNRTIs) or the drug Viread (tenofovir) were more likely to have low vitamin D levels.

Vitamin D is vital to bone formation, preservation of immune cells and control of blood pressure in the arteries. Our primary source for new vitamin D is exposure to the sun, notably ultraviolet B (UVB) light. In the general population, at least 29 percent of those who live in extreme northern or southern climates end up with low vitamin D levels in the winter and early spring. Low vitamin D levels have been repeatedly associated with bone problems and cardiovascular disease in studies of HIV-negative people.

Several studies have suggested that rates of vitamin D deficiency might be several times higher in people with HIV than in HIV-negative people. To confirm these rates and determine the factors involved in low vitamin D production in HIV-positive people, Nicolas Mueller, MD, from the University Hospital of Zurich, and his colleagues analyzed data from the 15,600 person Swiss HIV study.

Mueller’s team selected a small group of 211 people who had stored blood samples at various time points—before starting antiretroviral (ARV) therapy and 12 and 18 months after starting treatment. The team focused primarily on the roughly 100 people who’d had blood drawn in the spring (after months with little sunlight) and the fall (after peak sun exposure). As is the case in HIV-negative people, Muller and his colleagues considered 75 or more nanomolars per liter of blood (nmol/L) of 25-hydroxyvitamin D as the ideal, and 30 nmol/L or less as being deficient.

Vitamin D levels were particularly low at all time points in the study participants, with roughly half of the participants being vitamin D deficient during the spring. In fact, less than one quarter of the participants reached target vitamin D levels during the fall, and less than 10 percent hit target levels during the spring.

Without an HIV-negative control group, however, the researchers were unable to conclude that HIV-positive study volunteers were necessarily more likely to experience vitamin D deficiency.

As is the case in the general population, people with darker skin were much more likely to have low vitamin D levels at every time point. Use of Viread and NNRTIs such as Sustiva (efavirenz) and Viramune (nevirapine) was also associated with low vitamin D levels. Interestingly, the longer a person was HIV positive, the more protected they were from low vitamin D levels.

The authors are calling for further studies to confirm their results—particularly the association they found with low vitamin D levels and use of NNRTIs and Viread. The authors also state that this study suggests the need for better screening: “On the basis of our prevalence data and the growing recognition of vitamin D-related health benefits, we suggest systematic screening for vitamin D deficiency in all HIV-positive patients.”

Mueller and his colleagues then recommend that people with vitamin D deficiency consider taking supplements even though studies of supplementation in people with HIV have not yet been published.