Deep breath: about 60% to 80% of people with HIV smoke, compared to only 20% to 30% of negative folks. So it might seem logical that positive people have higher lung cancer rates (it’s the third most common malignancy for people living with the virus). But scientists say poor nutrition and HIV-related infections may further predispose positive smokers’ lungs to cancer.

A new study, reported in the Journal of AIDS, found that HIV puffs up lung cancer risk among all positive people—and by as much as 10 times among those aged 15 to 29. (Without HIV, young people don’t ordinarily get lung cancer, even if they smoke.) For positive people of all ages, the risk zooms up to four times the negative norm in the years just before and after AIDS sets in.

Study author Eric Engels, MD, of the National Cancer Institute, cites persistent and common HIV-related lung infections (think bronchitis and pneumonia) as possible contributors. Another, he says, is the low levels of antioxidant vitamins often seen in positive people—a problem because “those anti-oxidants protect cells from the damaging effects of tobacco.” (Dr. Engels recommends a balanced diet plus a multivitamin.)

San Francisco oncologist and former HIV doc Donald Abrams, MD, doesn’t let cigs off the hook: All these contributing factors just exacerbate tobacco’s damage. Abrams’ cancer-foiling formula: “Maintain a good weight,” he says, “with a body mass index lower than 25; exercise daily and have a diet rich in vegetables and whole grains.” While his recipe doesn’t guarantee reducing the HIV stress that fuels smoking, Abrams insists that quitting is the magic ingredient.