For women with heart disease, eating too many artery-clogging trans fats may increase their risk of dying suddenly from cardiac arrest, a new study suggests.

Trans fats, found largely in commercially prepared baked and fried foods, have become notorious in recent years because they not only raise “bad” LDL cholesterol - as the saturated fats in meat and butter do - but also lower levels of heart-healthy HDL cholesterol.

High trans-fat intake has been linked to coronary heart disease, in which fatty plaques build up in the heart arteries, sometimes leading to a heart attack.

But whether trans fats raise a person’s risk of dying suddenly from cardiac arrest has not been clear.

Sudden cardiac death is usually caused by rhythm disturbances in the heart’s upper chambers that render the organ incapable of pumping blood to the rest of the body. Some research suggests that trans fats could promote heart-rhythm abnormalities, but there is only limited evidence that they raise the odds of sudden cardiac death.

In the new study, researchers found that among nearly 87,000 U.S. women followed for 26 years, trans fat intake was not linked to the risk of sudden cardiac death across the whole study group.

However, when they looked only at women who had underlying coronary heart disease, there was evidence of an increased risk.

In this group, women who ate the most trans fats - typically getting 2.5 percent of their daily calories from the fats - were three times more likely to die of cardiac arrest than those who ate the least - getting less than 1 percent of daily calories in the form of trans fat.

Still, so few women with coronary heart disease died of sudden cardiac death during the study - 100 over 26 years - that the study lacked the statistical weight to clearly show that trans fats were a risk factor.

Researchers led by Dr. Stephanie Chiuve, of the Harvard School of Public Health in Boston, report their findings in the American Heart Journal.

Trans fats are formed during food processing when hydrogen is added to vegetable oil to make it solidify; foods that list so-called partially hydrogenated vegetable oil on the label contain trans fat.

Traditionally, that has included most commercially prepared baked and fried foods - including cookies, crackers, chips, breads and french fries - though, in recent years, manufacturers and restaurants have been increasingly reducing trans fats in their products.

The current study included 86,762 U.S. women involved in a long-running Nurses’ Health Study. Beginning in 1980 and every two to four years thereafter, the women completed detailed dietary questionnaires. Over 26 years of follow-up, 317 women died of cardiac arrest.

Among women who had not been diagnosed with coronary heart disease, there was no evidence linking trans-fat intake to sudden cardiac death once the researchers accounted for heart disease risk factors - like smoking, high blood pressure and excess weight.

When it came to women with coronary heart disease, however, the link between trans fats and sudden death held up even after other heart risk factors were weighed. The findings, according to Chiuve’s team, suggest that trans-fat intake “plays a greater role” in the risk of sudden cardiac death when coronary heart disease is already present.

The American Heart Association advises all adults to get less than 1 percent of their daily calories from trans fat - which amounts to about 2 grams for the typical American.

SOURCE: American Heart Journal, November 2009.