People with HIV are almost 50 percent more likely to have a heart attack than those who aren't infected with the virus - even after taking into account their other health risks, according to a new study.
Researchers aren't sure what explains the higher heart attack rate in HIV-positive people, but they speculate it's a combination of the effects of HIV itself and the antiretroviral drugs used to treat it.
"It's a complicated picture," said Dr. Matthew Freiberg, who led the new study at the University of Pittsburgh School of Medicine in Pennsylvania. "We're still trying to understand the mechanisms."
Just over 1.1 million people in the U.S. have HIV, according to the Centers for Disease Control and Prevention. Another 50,000 are infected each year.
Because treatment now allows HIV-infected people to live longer, researchers have started turning their attention to the other health problems those people face later in life, such as heart disease.
The new study included more than 82,000 U.S. veterans, almost all men. About one-third of them were infected with the human immunodeficiency virus.
During an average of almost six years, 871 of the study participants had a heart attack, of which 176 were fatal.
The researchers found that veterans with HIV were consistently more likely to suffer a heart attack than HIV-negative veterans in their 40s, 50s and 60s.
After Freiberg and his colleagues took into account participants' other heart risks - including high blood pressure, diabetes and drug and alcohol use - those with HIV were still 48 percent more likely to have a heart attack during the study period.
The findings suggest antiretroviral drugs accounted for at least part of the extra risk among people with HIV. But past studies have shown the virus itself also contributes to heart problems, according to Freiberg.
"It may be that HIV as it's in your body, like other infections, may be promoting an inflammatory response that is leading to these increased risks of heart attack," he told Reuters Health - but so far, that's just a theory.
Having hepatitis C or kidney disease was also tied to a higher chance of heart attack among veterans, the research team reported Monday in JAMA Internal Medicine.
Dr. Patrick Mallon, from the University College Dublin School of Medicine and Medical Science in Ireland, said past research showed a link between HIV and cardiovascular disease.
But it's been unclear whether other differences between groups of people with and without HIV - such as smoking rates and cholesterol levels, for example - could be driving the extra risk.
The new report helps clear that up by comparing two very similar groups of people where HIV status is one of the only differences, he noted.
"There have been a lot of signals for a very long time in HIV, and we're now starting to see people constructing studies properly that really give us some very clear answers," Mallon, who wrote a commentary accompanying the new study, told Reuters Health.
HIV has also been linked to disturbances in fat use and storage in the body.
Mallon and Freiberg agreed that people with HIV should make sure they have their blood pressure and cholesterol checked regularly and do whatever else they can to prevent heart disease - such as quitting smoking.
"There is a lot that the individual can do to mitigate their risk along the lines of lifestyle interventions," Mallon said. "At a personal level, that would be step number one."