People who are wondering whether they should take cholesterol-lowering medications may be scratching their heads today, more confused than ever.

Last week the American Heart Association and the American College of Cardiology released new cholesterol-treatment guidelines, and today those guidelines are being criticized by two Harvard Medical School professors in a medical journal. They say that the formula used may be flawed and may overestimate people’s risk.

A cardiologist who worked on the guidelines says he stands by them, but he says they will be updated over time. “These aren’t set in stone. As more high-quality research becomes available, we will incorporate it into the guidelines to improve patient care,” says Donald Lloyd-Jones, chairman of the department of preventive medicine at Northwestern University.

Heart experts who wrote the new guidelines say that any flaws in the formula are small and should not delay implementation of the guidelines, which expand how many people should consider taking cholesterol-lowering statin drugs such as Lipitor and Zocor or their generic forms.

For years, doctors prescribed statins largely based on patients’ cholesterol levels, especially their LDL (bad) cholesterol. The new guidelines advise doctors to take a broader look at a patient’s overall risk, rather than just cholesterol numbers.

The guidelines identify four high-risk groups who could benefit from statins:

• People with the sort of super-High cholesterol that sometimes runs in families, as evidenced by an LDL of 190 milligrams per deciliter or higher;

• Patients with pre-existing heart disease, such as those who have had a heart attack;

• Those ages 40 to 75 who have diabetes;

• People 40 to 75 with at least a 7.5% risk of developing cardiovascular disease in the next decade, according to a formula described in the guidelines.

While statins have been widely prescribed to reduce the risk of heart attacks, the new guidelines recommend that they also be considered for people at high risk of stroke. The number of adults potentially eligible for statins will rise from about 15.5% today to 31% based on the new guidelines and could lead doctors to prescribe the drugs to millions more people.

The guidelines have been a hot topic of discussion this week at the American Heart Association’s Scientific Sessions in Dallas. At the heart of the debate: The formula used to identify the people ages 40 to 75 with at least a 7.5% risk of developing cardiovascular disease over the next decade.

The Harvard professors applied the risk formula to several large studies and found it overestimated people’s risk of heart attack and stroke. They report their findings in a commentary Tuesday in the medical journal The Lancet.

“If you really have a 4% risk of heart attack or stroke, the formula might tell you have an 8% risk,” says commentary co-author Nancy Cook, a biostatistician at Harvard and Brigham and Women’s Hospital in Boston.

“It’s not perfectly clear what’s going on, or if the formula is wrong or not,” she says. “We need to figure out why the estimates are different before we use it to extensively prescribe medications.”

She advises doctors to wait before using the new risk calculator. “It could be a very simple fix such as changing one number in the calculations. It’s also possible that the formula is correct, but we have to resolve the discrepancies.”

The other co-author, Paul Ridker, a cardiologist at Brigham and Women’s Hospital in Boston, said in a statement that he strongly supports the key messages of the new guidelines and believes questions raised about the risk calculator should be relatively easy to address.

Lloyd-Jones says the committee that wrote the cholesterol guidelines stands behind its work. He says the Harvard experts’ data used people who “were extremely healthy and much healthier than the general population.”

Still, he says, “if new data become available, we’ll update the guidelines. We are eager to make them even better.”

In the meantime, if you’re in a high-risk group, that’s “an indicator that you and your doctor should have a discussion. You should at least consider statins,” Lloyd-Jones says. The new guidelines are supposed to be “the start of a conversation, not the end of the conversation,” between patients and their doctors, he says.

Statins are “very effective, really cost-effective and very safe for the majority of Americans,” he says. “Even if a side effect occurs, it almost always goes away by reducing the dose or stopping the drug.”

Underlying all for these guidelines is a heavy emphasis on lifestyle modification, Lloyd-Jones adds. “That means if you aren’t doing any physical activity, do some. If you are doing some, do more. Decrease the amount of time you spend sitting in front of a screen. Eat mostly fruits and vegetables supplemented with lean protein. Try to avoid fatty and sugary foods. And if you smoke, quit as soon as you can - and more important, don’t ever start.”

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Contributing: The Associated Press