Severe forms of the itchy skin condition, psoriasis, should be considered a risk factor for heart attack, a new study suggests. Researchers who studied medical records for more than 680,000 British patients found that people in their 40s with severe psoriasis were more than twice as likely to suffer a heart attack than people without the skin disease.

The link may be inflammation, the body's normal response to injury and infection, which plays a role in both heart disease and psoriasis, researchers said.

Mild psoriasis slightly raised the risk for heart attack, by 20 percent for people in their 40s. But study co-author Dr. Joel Gelfand of the University of Pennsylvania said people with mild psoriasis "on their elbows and knees" shouldn't worry.

"I don't want to overly alarm people," Gelfand said. "If you have psoriasis you should see a physician and go through a screening to make sure you don't have other cardiovascular risk factors."

The study, which was partly funded with a grant from the maker of a psoriasis drug, appears in Wednesday's Journal of the American Medical Association.

Psoriasis causes itchy, painful patches of thick, red, scaly skin. The chronic disease is thought to start with the immune system overreacting and targeting the body's own cells. More than 5 million Americans suffer from it, but most do not have the severest form.

There isn't a precise definition of severe psoriasis. About 100,000 Americans have 10 percent or more of their skin affected, and an estimated 500,000 say psoriasis is a significant problem for them in their everyday life.

People with psoriasis are more likely to smoke and to have diabetes, high blood pressure and high cholesterol. But the researchers found that even when they took those risk factors into account, psoriasis still increased the risk of heart attack.

Dr. Fred Leya of Loyola University Health System said cardiologists have long noticed the connection between psoriasis and heart disease. The study should encourage doctors to be more aggressive at controlling cardiovascular risk factors like cholesterol in their patients with psoriasis, he said.

"This is not a breakthrough discovery, but an important documentation of the facts," said Leya, who wasn't involved in the study.

Dr. William Weintraub, a cardiologist and research director at Christiana Care Health System in Newark, Del., questioned the study's importance for patients.

"Severe psoriasis is relatively uncommon, and the risk for heart attack with mild psoriasis is relatively minor," said Weintraub, who was not involved in the study.

Based on their findings, the researchers predict that 1 out of 623 people with severe psoriasis in their 40s will have a heart attack related to their psoriasis each year, Gelfand said. For mild cases, 1 in 3,646 people in their 40s would have a heart attack each year.

Gelfand and another co-author reported financial ties to companies investigating drug treatments for psoriasis. The study was funded by the National Institutes of Health and a grant to University of Pennsylvania from Cambridge, Mass.-based Biogen Idec Inc., which has a psoriasis drug in development.