There’s good news and bad news about cholesterol in the U.S., according to a recent study published in JAMA. Researchers have found that the prevalence of high LDL or "bad" cholesterol among American adults decreased by about a third between 1999 and 2006. However, a high percentage of adults are not being tested or treated for high cholesterol.

Researchers at the Centers for Disease Control and Prevention looked at data for more than 7,000 adults four times between 1999 and 2006. They looked at the prevalence of screening, current use of cholesterol-lowering medication, and high LDL cholesterol levels in each time period.

Overall prevalence for high LDL-C levels decreased from 31.5 percent in 1999-2000 to 21.2 percent in 2005-2006.

However, there were no significant changes observed in the weighted age-standardized screening rates from 1999-2000 to 2005-2006. Among participants with high LDL cholesterol levels, 35.5 percent were unscreened, 24.9 percent were undiagnosed, and 39.6 percent were untreated or inadequately treated in 2005-2006.

According to the Mayo Clinic, high cholesterol can cause fatty deposits in the blood vessels, which can lead to clogged arteries. This can lead to an increased risk for heart attack and stroke.

High cholesterol is largely preventable and can be avoided by eating a healthy diet and getting regular exercise.