The cholesterol in your diet comes in two kinds: the artery-clogging “bad” LDL (low density lipoprotein) cholesterol and the artery-cleansing “good” HDL (high density lipoprotein) cholesterol. But now it seems that for some people, the “good” cholesterol may actually be bad for the heart, according to a study published in Arteriosclerosis, Thrombosi, and Vascular Biology, a journal of the American Heart Association, and reported in a press release from the University of Rochester Medical Center.

For the study, researchers studied 767 people who’d already suffered one heart attack and were deemed at high risk of further heart trouble. They followed these patients for two years while tracking their blood levels of HDL cholesterol and of C-reactive protein (CRP), a protein the body creates to treat inflammation.

Researchers found that the patients with above-average levels of CRP were at greater risk for heart disease as their levels of HDL cholesterol went up. These high-risk patients naturally produced higher levels of two inflammation-related proteins, suggesting that the bad reaction to “good” HDL cholesterol comes from a mix of inflammation and genetics.

The authors of the study hope that by screening patients for genes that cause overproduction of these inflammation-related proteins, docs can identify who should and shouldn’t increase their HDL cholesterol levels. This research will be more important than ever as pharmaceutical companies develop drugs to raise HDL cholesterol.

“Our research is oriented around the ability to better identify patients at high risk. Identifying these patients and determining what puts them at high risk may be useful in choosing treatments tailored to the specific needs of particular patient subgroups. This gets us another step closer to achieving the goal of personalized medicine,” said the study’s lead author, James Corsetti, MD, PhD, professor of Pathology and Laboratory Medicine at the University of Rochester Medical Center.

Click here to read about the effects of “good” HDL cholesterol on memory loss.