Having a “normal” LDL cholesterol level may not protect you from a heart attack.

That’s the message of a national study that looked at more than 136,000 patients admitted to hospitals for heart attacks from 2000 to 2006.

The surprise? Nearly three-quarters of them had low-density lipoprotein (LDL) cholesterol levels lower than 130 mg/dL, a level considered to be normal for anyone without a history of heart disease or diabetes under current government guidelines.

What’s more, half of the heart attack patients in the study had LDL cholesterol levels under 100, a number currently considered to be optimal for most people.

“I think what this illustrates is that the thresholds in the guidelines may need to be reconsidered,” says Gregg C. Fonarow, MD, a cardiologist at Ronald Reagan UCLA Medical Center in Los Angeles and lead author of the study, which was published in the January 2009 issue of the American Heart Journal.

Dr. Fonarow says the risk for cardiovascular events in the study appeared to be low for LDL levels below 60 mg/dL.

Those numbers, while difficult to obtain, are good targets for people who have other risk factors for cardiovascular disease like a history of smoking, diabetes, or people with inflammatory conditions like rheumatoid arthritis.