Should a 76-year-old who doesn’t have heart disease, but does have certain risk factors for developing it, take a statin to ward off heart attacks or strokes?

You’d think we’d have a solid answer to this question. These widely prescribed medications lower cholesterol to reduce cardiovascular disease, the nation’s most common killer, and get much of the credit for the nation’s plummeting rates of heart attacks and strokes.

When they entered common use in the 1990s, “it was very exciting,” said Dr. Ariela Orkaby, a geriatrician at the Harvard Medical School and lead author of a new study on statins in older adults.

“Suddenly you had a drug that could reduce the risk of heart attack and stroke by 20 or 30 percent or more.”

So current medical guidelines recommend statins for people in that no-heart-disease category, a strategy called primary prevention — but only for those up to age 75. Yet almost half of adults aged 75 and older take statins, the Centers for Disease Control and Prevention has reported.

Some of those people probably are taking drugs that aren’t helping and can cause problems, researchers and geriatricians say.

On the other hand, some older patients who likely would benefit from statins aren’t taking them.

“This is a situation that makes most doctors very uncomfortable,” said Dr. Sei Lee, a geriatrician at the University of California, San Francisco. “Some feel these drugs have been successfully used in younger patients, so why not use them?”

So why not?

“We don’t have good specific data for people without known heart disease over age 75,” Lee said. “Are statins helpful or harmful for them? The honest answer is, we don’t know.”

To be clear: Statins make sense for adults of any age who already have heart disease, who have suffered a heart attack or stroke, or who have had arteries unblocked with a procedure like stenting. This is called secondary prevention.

In 2013, the American College of Cardiology and the American Heart Association issued a series of statin recommendations for primary prevention, relevant to adults up to age 75 who have high cholesterol or diabetes, or who for other reasons face an estimated 7.5 percent risk or greater of developing heart disease within 10 years.

Three years later, the U.S. Preventive Services Task Force similarly recommended statins for primary prevention in people ages 40-75 who had risk factors like high cholesterol, diabetes, high blood pressure or smoking, with a 10-year disease risk of 10 percent or greater.

But for people over age 75, both panels agreed, there was not sufficient evidence to reach a conclusion.

As with many clinical trials, the major statin studies mostly haven’t included patients at advanced ages.

“The oldest patients enrolled have been up to age 82,” said Dr. Michael Rich, a geriatric cardiologist at Washington University School of Medicine, referring to the PROSPER study published in 2002.

The authors of that study followed 5,800 patients for three years and found that pravastatin provided secondary, but not primary, prevention against cardiovascular events.

But Dr. Paul Ridker, a self-described “statin advocate” who directs the Center for Cardiovascular Disease Prevention at Brigham and Women’s Hospital in Boston, gets irked at the argument that we don’t know enough to give statins to older patients without heart disease.

“I don’t believe there’s any doubt that statin therapy is effective for primary prevention in older adults,” Ridker said. He cites a recent reanalysis of data from two major studies showing that patients over age 70 taking statins experienced the same reductions in cardiovascular events and mortality as younger ones.

Orkaby and her Harvard colleagues hoped to help resolve such questions with their recent study, published in the Journal of the American Geriatrics Society, comparing physicians over age 70 who took statins for primary prevention with those who didn’t.

The team matched each group for 30 variables and found that over an average of seven years, statin-takers had an 18 percent lower death rate, though not a statistically significant reduction in cardiovascular events.

In the same issue, though, an editorial co-written by Rich called statin use for primary prevention in older patients “an unresolved conundrum.”

The physician study was observational, so can’t establish causes, he pointed out. And it followed a group that was healthier than average, and all male. Moreover, he said, the findings suggest the drugs had more benefit for those under age 77.

It can take two to five years for a statin to pay off preventively, so a healthy 80-year-old expected to live that long might well opt to take one or to continue taking one.

“It’s a well-known, proven therapy that might prevent a devastating illness,” Orkaby said.

By trying different statins at different dosages, she said, patients usually can find a comfortable regimen.

On the other hand, she routinely stops statins for nursing home residents — who are already very ill — or for elders who are frail, have life-limiting diseases, or grapple with an already daunting number of prescriptions.

“There are a lot of unknowns,” Orkaby said. “We don’t want to do harm by prescribing a medication. And we don’t want to do harm by withholding it.”