Researchers say better diets and changes in the food industry have spurred cholesterol levels in the U.S. to drop over the last decade and a half.

The study, published in the journal JAMA Cardiology, looked at national survey data to compare total cholesterol levels in 39,000 adults over an eight-year span.

Lower cholesterol could help to account for a decline in death rates from heart disease and stroke that the Centers for Disease Control and Prevention reported earlier this year.

The researchers found that total cholesterol levels fell from 204 milligrams per deciliter of blood in 1999-2000 to 189 in 2013-2014.

The CDC says adults should aim for total cholesterol levels under 200.

The study's authors said the removal of trans-fatty acids from foods could help explain improved cholesterol levels.

Trans fats like partially hydrogenated oils have been used in foods like frosting and shortening to improve taste and texture.

Last year, the The FDA officially banned trans fats as an additive, but many companies had been phasing those ingredients out of products voluntarily.

Read More:

• Why Americans' Cholesterol Levels Are Improving (LiveScience)
• Trends in Total Cholesterol, Triglycerides, and Low-Density Lipoprotein in US Adults, 1999-2014 (JAMA Cardiology)