In a 20-year study in Britain of men who had no coronary risk factors other than high LDL levels and no evidence of heart disease, 40 milligrams a day of pravastatin (Pravachol), a relatively weak statin, reduced coronary deaths by 28 percent.

Also important are the likely mechanisms behind such protection. In addition to lowering blood levels of LDL, statins reduce inflammation, now recognized as an important risk factor for heart disease, and they stabilize the plaque that narrows coronary arteries. Most heart attacks happen when a chunk of plaque becomes unstable, breaks loose and obstructs a major artery feeding the heart.

There may be other important benefits. A review of 36 studies involving more than 3.2 million people found that statin use reduced the risk of blood clots in a limb or lung by 15 to 25 percent. Also enticing is the finding among 400,000 men and women on Medicare linking statin use to a lower risk of developing Alzheimer’s disease. To be sure, this is just an association, not a controlled clinical trial, but one possible explanation for the link is that cholesterol plays a role in processing beta-amyloid, plaques of which are a hallmark of Alzheimer’s.

None of this means that every adult over 50 should be on a statin. Trials involving hundreds of participants with differing cholesterol levels and coronary risk factors have shown that those who are at the low end of the risk profile are unlikely to benefit, at least in terms of cardiovascular disease.

Currently, doctors and patients can use the Cardiovascular Risk Calculator to determine where on the risk spectrum someone between the ages of 40 and 79 falls. Those calculated to face a risk of experiencing a cardiovascular event over the next 10 years below 5 percent are considered low-risk; a risk level between 5 percent and 7.4 percent is labeled borderline; a level of 7.5 percent to 19.9 percent is intermediate, and a level of 20 percent or higher is considered high.

In the latest guidelines from an expert committee of cardiologists, high-risk patients, including anyone who has already had a cardiovascular event, should be advised to start taking a statin, with the goal of lowering their cholesterol level by more than 50 percent. The goal for intermediate-risk patients is a 30 percent reduction in their LDL-cholesterol level.

Those who are uncertain about the extent of their risk or who hesitate to take a statin based only on a medical profile suggesting their cardiovascular risk is relatively high could opt for a CT scan of the heart to determine their coronary artery calcium score. The score indicates how much hardened plaque may line the arteries critical to their heart’s health.