A popular cholesterol-drug taken by millions of Americans may be interfering with a good night's sleep, according to new research reported at the American Heart Association’s Scientific Sessions 2007 in Orlando, Fla. this week.

For the large study, researchers compared two types of cholesterol-lowering drugs. They looked at sleep patterns of people who took the statin drug simvastatin, sold under the brand Zocor, which is lipophilic (soluble in fats), and people who took Pravachol or pravastatin, which is hydrophilic (soluble in water). What they found was that people who took Zocor had significantly worse sleep compared to people who took Pravachol.

“The findings are significant because sleep problems can affect quality of life and may have adverse health consequences, such as promoting weight gain and insulin resistance,” said lead study author Dr. Beatrice Golomb, associate professor of medicine and family and preventive medicine at the University of California at San Diego School of Medicine, in a news release.

Because simvastatin is fat soluble,it can more readily penetrate cell membranes and cross the blood-brain barrier into the brain. The brain controls sleep, and many of the brain’s nerve cells are wrapped in a fatty insulating sheath called myelin, the researchers said.

Golomb and her colleagues tested more than 1,000 healthy adult men and women for six months in a randomized, placebo-controlled trial using simvastatin, given at 20 milligrams, pravastatin at 40 milligrams, or a placebo. They assessed outcomes using two different rating scales.

“A significantly greater number of individuals taking simvastatin reported sleep problems than those taking either pravastain or the placebo,” said Golomb. “On average, the lipophilic statin had a greater adverse effect on sleep quality.”

Researchers did not include patients with heart disease or diabetes due to concerns about assigning these people to placebos.

“Patients taking simvastatin who are having sleep problems should consult with their doctor,” said Golomb. “Sleep deprivation is a major problem in a minor number of people.”

The study was funded by The National Heart, Lung, and Blood Institute of the National Institutes of Health.