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(CNN) —  

Half of all people who are prescribed statins for the prevention of heart disease fail to reach target cholesterol levels two years later, according to a new study.

Researchers used data submitted to the UK Clinical Practice Research Datalink by 681 family doctors. The study group was made up of 165,411 people who were prescribed a statin between 1990 and 2016 and who had not been treated for heart disease or stroke before the prescription.

They defined an “appropriate” response to statin therapy as a reduction of 40% or more in LDL or “bad” cholesterol, as recommended by the UK’s National Institute for Health and Care Excellence.

Fewer than half of all people enrolled over the 26-year study period – 48.8% – achieved target cholesterol levels at the two-year followup mark, with just over half – 51.2% – falling short, according to the study, published Monday in the journal Heart.

After taking into account differences in age and underlying medical conditions, the researchers found that people who did not lower their LDL cholesterol enough were 22% more likely to develop cardiovascular disease than those who did lower it.

Statins work by lowering LDL cholesterol or low-density lipoprotein, which in turn lowers the risk of heart attack and strokes. In the United States, the American Heart Association and the American College of Cardiology recommend that doctors use a 10-year risk calculator to determine which patients may benefit from such therapy.

Over 78 million Americans, or just over a third of all adults, are eligible for statin therapy or are taking a statin, according to the US Centers for Disease Control and Prevention. In the UK, over 7 million adults take these drugs, according to the British Heart Foundation.

The number of Americans who don’t reach target cholesterol levels after starting a statin is probably similar to the study findings, explained Dr. David Fischman, professor of medicine and co-director of the Cardiac Catheterization Laboratory at Thomas Jefferson University Hospital, who was not involved in the study.

“Taking care of patients, treating them with statins, is a job. It’s a lot of work. It’s not easy. It’s a time commitment to get it right,” Fischman said. “When you start someone on a cholesterol medication, you’re supposed to check their cholesterol in four to 12 weeks and then make adjustments, and this highlights the importance of doing that.”

In addition to the amount of work and commitment required to optimize cholesterol levels, the authors explain that genetic factors and differences in adherence to the prescribed regimens may explain some of the variations in response to statin prescriptions, and they call for “personalized” medicine.

“Currently, there is no management strategy in clinical practice which takes into account patient variations in [low density cholesterol] response, and no guidelines for predictive screening before commencement of statin therapy,” the researchers said.

In an editorial published alongside the study in Heart, Dr. Márcio Bittencourt, a cardiologist at the University Hospital of São Paulo in Brazil, explains that physician prescribing practices may also account for some of the differences seen in the research. Those who achieved their cholesterol goals were more likely to be prescribed more potent statins, probably because the group also started with higher levels of cholesterol, he said.

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The research has several limitations. As an observational study, it cannot establish cause and effect. The exact dosage of statins prescribed and patients’ compliance to the prescriptions were not within the scope of the research.

“The take-home message for me is, we have to do a good job. We have to follow through, not just the physician but the patient, too,” Fischman said. “Because if we don’t, [patients who don’t reach target cholesterol levels] are not going to fare as well.”