Reported by Julielynn Wong, MD:

Cholesterol levels among U.S. adults have dropped an average of 10 points in two decades, a new study found, but cardiologists say Americans still have a lot to do to improve their health.

The survey-based study of more than 35,000 men and women found a decrease in total cholesterol from an average of 206 to 196 mg/dL as well as a 13-point drop in low-density lipoprotein cholesterol - better known as LDL or "bad" cholesterol. The results held up after adjusting for age, gender, race and obesity, and were even seen in adults who had never taken cholesterol-lowering medications.

"These findings are important because individuals with high levels of total or 'bad' cholesterol have a greater chance of developing heart disease, one of the leading causes of death in the United States," said lead author Margaret Carroll, a survey statistician at the National Center for Health Statistics at the Centers for Disease Control and Prevention in Hyattsville, Md.

The drop in cholesterol among adults not taking cholesterol-lowering drugs suggests statins aren't the only factor, according to Carroll. Another possible contributor, she said, is the decrease in dietary trans-fats - a form of fat known to raise cholesterol.

Since 2003, the Food and Drug Administration has mandated that trans-fats be labeled on food products. And some community and state health departments have required restaurants to limit trans-fats on their menu items.

While the drop in cholesterol is good news, other factors, such as smoking, obesity, poor diet, lack of exercise, high blood pressure and alcohol use, can also raise the risk for heart disease, according to Dr. Dariush Mozaffarian, a cardiologist and associate professor of medicine and epidemiology at Harvard Medical School, who was not involved with the study.

"Physical activity has been relatively flat overall," he said, adding that obesity rates have actually increased since the 1990s.

"We're not eating enough of the healthy things," Mozaffarian added. "Things like fruits, vegetables, nuts, vegetable oils, and whole grains."

So it may be too early to rejoice.

"We've gone from a F+ to a D- in our report card. That's great," Mozaffarian said. "But we want to get to an A. We have a long way to go."