(USA TODAY) -- Cholesterol levels in the USA have improved significantly over the past 20 years, possibly because of a decreased intake of trans fats in people's diets and the increased use of cholesterol-lowering drugs, says a government study out Tuesday.

"This is a favorable trend and a continuation of what we have seen in the past," says Brian Kit, one of the study's authors and a medical epidemiologist with the Centers for Disease Control and Prevention (CDC). Previous research has documented consistent declines in total cholesterol since 1960.

High levels of total cholesterol and bad (LDL) cholesterol and low levels of good (HDL) cholesterol increase your risk of coronary heart disease, according to the American Heart Association. "Reductions in cholesterol have contributed substantially to the decline in heart disease," says Donna Arnett, president of the heart association.

Although the rate of death from cardiovascular disease declined by 31% from 1998 to 2008, the disease is still the leading cause of death in the USA.

The group recommends keeping your total cholesterol to less than 200 mg/dL (milligrams per deciliter of blood) to lower your risk of heart disease. Having a bad cholesterol level below 100 is considered optimal, the association says. A good cholesterol of 60 mg/dL and above is considered protective against heart disease.

Total cholesterol is the measure of good cholesterol, bad cholesterol and triglycerides (blood fats).

Bad (LDL) cholesterol is produced naturally by the body, and many people inherit genes that cause them to make too much, the heart association says. Eating saturated fat, artery-clogging trans fats and dietary cholesterol also increases the level.

CDC researchers studied the cholesterol levels of nearly 38,000 people who took part in National Health and Nutrition Examination Surveys from 1988 to 2010. These are the gold standard of health surveys because people's cholesterol levels were actually measured. Among the findings in the Journal of the American Medication Association:

Average total cholesterol dropped from 206 in 1988 to 196 in 2010. In 1960, cholesterol levels were an average of 222.

Average bad (LDL) cholesterol fell from 129 in 1988 to 116 in 2010.

Good (HDL) cholesterol increased modestly from about 51 to 53.

Non-HDL cholesterol (all the bad cholesterol combined) decreased from 155 to 144.

The percentage of adults taking cholesterol-lowering medications increased from 3.4% in 1988 to 15.5% in 2010.

People who were not on cholesterol-lowering medications had improvements in their total cholesterol, Kit says.

Overall, both men and women, all ethnic groups and even obese people reduced their total cholesterol, Kit says. "In another study, we found similar improvements in blood cholesterol among children during this time period."

Kit says the improvements may be due to declines in smoking and reductions in foods high in trans fats.

Arnett says, "We are doing well as a population in terms of lowering our cholesterol levels. We've worked to reduce the amount of trans fats in our diet in processed foods and fast food."

A recent study showed that the amount of trans fats in the blood of white adults dropped dramatically from 2000 to 2009, indicating a decreased consumption.

In recent years, many food companies have taken trans fats out of their products, and many big restaurant chains have switched to healthier oils.

Copyright 2012 USA TODAY, a division of Gannett Co. Inc.