A session on side effects of antiretroviral therapy at the 2010 International AIDS Conference in Vienna, Austria included a presentation on bone loss in people with HIV and its possible causes and risk factors. The presenter, Dr. Patrick Mallon, confirmed that people with HIV experience greater bone loss than people without HIV; however, he also argued that the link between bone loss and antiretroviral medications, weight, and vitamin D deficiency remains unclear.

Dr. Mallon, an infectious diseases specialist at Mater Misericordiae University Hospital in Dublin and a lecturer at the University College in Dublin, began his talk by confirming that people with HIV do have higher rates of bone loss and low bone density than people without HIV.

“We now have a wealth of data from various populations around the world that consistently shows very high rates of low [bone mineral density] in HIV-infected patients,” said Dr. Mallon.

Low bone mineral density is associated with an increased risk of bone fractures.

It is not yet clear what causes bone loss in HIV-positive adults; however, “one consistent finding that’s come through from clinical trials is that patients [starting] antiretroviral treatment experience bone loss,” said Dr. Mallon.

Researchers are currently uncertain whether this is a side effect of the antiretroviral drugs or from recovery of the immune system once treatment starts. A study in 2009 by researchers at UCLA suggested that immune system activation can lead to bone loss and osteoporosis.

Dr. Mallon argued that bone loss in adults with HIV probably results from both the drugs and the immune system recovery.

“There is not a single antiretroviral regimen that is being tested that hasn’t resulted in bone loss upon antiretroviral initiation,” he said. However, “changes in bone mineral density upon antiretroviral initiation will change considerably depending on which antiretroviral medication you start.”

Research has shown, for example, that patients taking nucleoside reverse transcriptase inhibitor (NRTI) treatment regimens containing Viread (tenofovir) exhibit greater bone loss than those containing Ziagen (abacavir).

Additionally, patients using protease inhibitor treatment regimens experience greater bone loss than those on non-protease inhibitor regimens, particularly in the spine.

Dr. Mallon also discussed two other factors traditionally associated with bone loss: low body mass index (BMI) and vitamin D deficiency.

People with a low BMI are usually at higher risk of low bone density, and this appears to be the case for people with HIV as well. “Body mass index has consistently [been shown to have] a close association with low [bone mineral density] and HIV,” said Dr. Mallon.

However, most studies showing low BMI is a risk factor for bone loss have been done with much older populations, and Dr. Mallon argued that this may not hold for younger HIV-positive people.

“Low BMI, especially in young gay men, may not be necessarily associated with negative health,” said Dr. Mallon.

However, he added, there is some evidence that “patients with lower BMI who are HIV positive actually have a faster loss of [bone mineral density] over time.”

More studies will be necessary to determine whether a low body mass index is truly a risk factor for faster bone loss in people with HIV regardless of age.

Finally, Dr. Mallon presented the results of several recent studies to refute claims that low vitamin D levels contribute to the low bone mineral density seen in people with HIV.

Although it is true that HIV-positive adults tend to be deficient in vitamin D, Dr. Mallon argued that this is true of the HIV-negative population as well. “The low vitamin D picture is really a picture that’s spread throughout society,” he said.

Furthermore, studies of people in the early stages of HIV infection have shown low bone mineral density but no vitamin D deficiency, and other studies have suggested that the type of bone loss in people with HIV is not consistent with deficiencies in vitamin D.

“All of these results really prove vitamin D, in my view, is on a much lower [level] in terms of its potential to cause low [bone mineral density]” than other factors, said Dr. Mallon.

To close, Dr. Mallon advocated a “more formal assessment of bone health” for all adults with HIV, specifically bone mineral density screening.

“We should be introducing the screening and we should be introducing treatment for these patients in order to maximize the reduction in fractures that our patients will experience over the next decade,” he said.

Dr. Mallon also noted that studies are currently underway to see if bisphosphonate supplements can help safely reduce bone loss upon starting antiretroviral therapy.

For more information, please see the AIDS 2010 webpage on the Kaiser Family Foundation website.