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.