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Within two years after a heart attack, nearly one in five people stop taking life-saving cholesterol-lowering drugs known as statins, according to a new U.S. study.

And nearly two in five end up taking the drugs in lower doses or less often than they should, the researchers report in JAMA Cardiology.

a procedure to check cholesterol levels. Geoff Caddick / PA via AP file

"From a societal perspective, we need to make sure the highest-risk individuals are being treated with guideline-directed therapy," said senior author Dr. Robert Rosenson, a professor of cardiology at the Icahn School of Medicine at Mount Sinai in New York City.

The 2013 guidelines from the American College of Cardiology and the American Heart Association (ACC/AHA) recommend high-intensity statins for people 75 and younger who have coronary heart disease. The pills help prevent future cardiovascular events.

Statins include Lipitor, which is sold generically as atorvastin, and Crestor, also known as rosuvastin. They work by inhibiting the production of cholesterol in the liver.

Rosenson told Reuters Health his team had previously found low use of high-intensity statins in people with previous heart attacks. The new study aimed to find out what traits were associated with discontinuing or reducing statins.

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Related: Study Confirms Who's Helped by Statins

The researchers analyzed data collected from 57,898 people aged 66 and older on Medicare, the publicly funded health insurance for the elderly and disabled.

Everyone in the study was hospitalized for a heart attack at some point between 2007 and 2012. They also all filled a prescription for a high-intensity statin within 30 days of leaving the hospital.

After six months, about 59 percent of people ages 66 to 75 continued to regularly take their high-intensity statin. About 9 percent switched to a lower dose. About another 17 percent took the medications irregularly and about 12 percent stopped taking the drugs altogether.

After two years, only about 42 percent were regularly taking their statins. About 13 percent had switched to a lower dose. About 19 percent were taking the drugs infrequently and another 19 percent had stopped the drugs altogether.

The researchers saw similar results for people age 75 and older, for whom the ACC/AHA guidelines generally recommend a slightly lower dose of statins.

African Americans and Hispanics, and those taking statins for the first time, were less likely to regularly take their medication.

People were more likely to regularly take their statins if they saw their cardiologists often, took part in cardiac rehabilitation programs or were also enrolled in Medicaid, the health insurance program for low-income patients administered by states and the federal government.

The researchers conclude that lower costs, more cardiologist visits and cardiac rehabilitation may boost the number of people staying on high-intensity statins and ultimately reduce the risk of future heart attacks.

Rosenson noted that statins are now available in less expensive generic forms. "You can’t say that cost accounts for all of this," he said.

People should know that statins have benefits beyond just lowering low-density lipoprotein (LDL), also known as "bad" cholesterol, he said. They also have anti-inflammatory benefits.

"I think what the public needs to know is discontinuing or down-titrating your statins is associated with a greater risk of having a second heart attack and being in the hospital with a cardiovascular event that may result in a procedure that results in higher healthcare cost for them and the entire public," he told Reuters Health.