After years of steady progress, declines in cardiovascular mortality appear to have stagnated since 2008 and heart disease remains the leading cause of death in the United States. Scientists attribute the pause in progress to a recent worsening of cardiovascular risk factors, including blood pressure and blood sugar control, among U.S. adults. However, little is known about trends in another major modifiable risk factor for cardiovascular disease; lipid concentrations—the amounts of several types of fats (such as cholesterol and triglycerides) in the blood that can line and clog the arteries, making the heart work harder than necessary.