NEW YORK — Drugs like Pfizer’s Lipitor and healthier diets containing fewer trans fats have led to lower cholesterol levels in the United States in the past two decades, even as obesity rates soared, a study found.

Total cholesterol declined 5 percent on average between 1988 and 2010, while “bad” cholesterol, or LDL, dropped 10 percent and “good” cholesterol, or HDL, rose 3.4 percent, according to research published Tuesday in the Journal of the American Medical Association. The number of people using cholesterol-lowering medicines rose to 16 percent in 2007-2010 from 3 percent in 1988-1994.

High cholesterol is a major risk factor for heart disease and stroke, according to the American Heart Association. Less smoking, better diets and widely prescribed cholesterol-lowering medicines have all helped to lower levels in the U.S., the authors said. About one-third of American adults are obese.

“Even though we’ve had this increase in obesity, some of those negative consequences have been balanced by the reductions of smoking and trans fats in our diet,” said Donna Arnett, president of the Dallas-based American Heart Association, in a telephone interview Monday. “In the U.S., we have been improving our cholesterol levels and improving our cardiovascular health and that’s good news.

Researchers in the study analyzed data from 37,810 patients who were part of the National Health and Nutrition Examination Survey from 1988-1994, 1999-2002 and 2007-2010.

They found that total cholesterol fell to 196 milligrams per deciliter of blood in 2007-2010 from 206 mg/dL in 1988-1994, dropping below the target of 200 mg/dL set by Healthy People 2010, which provides 10-year national health objectives. Bad cholesterol levels, or LDL, dropped to 116 from 129, while good cholesterol, or HDL, rose to 52.5 from 50.7.

The American Heart Association recommends that total cholesterol be less than 200 to prevent heart attacks and strokes, while LDL be less than 100 and HDL be above 60 to protect against heart disease.

Even those not taking the medications saw a drop in cholesterol levels, which the study said was probably due in part to “a decrease in consumption of trans-fatty acids or other healthy lifestyle changes.”

“They are unlikely to be the result of changes in physical activity, obesity or intake of saturated fat,” the researchers wrote. Obese adults had a decline in total cholesterol and LDL but not an increase in HDL levels, the authors said.

The number of obese American adults has more than doubled in the past 30 years to about 78 million, according to the Atlanta-based Centers for Disease Control and Prevention.

More research is needed to better understand what exactly is behind the decrease in cholesterol levels since the decline can’t be explained by cholesterol-lowering medicines alone, said lead study author Margaret Carroll, a survey statistician at the National Health and Nutrition Examination Survey, part of the CDC, in Hyattsville, Md.

“What we presented is data for the population as a whole, she said in an telephone interview yesterday. “And the good news is total and bad cholesterol have gone down and we’ve seen an increase in the good cholesterol.”

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