As if a blow to one’s masculinity weren’t bad enough. Researchers now say that for men over 40, having trouble getting or maintaining an erection is often a sign of something more worrying: cardiovascular disease. Indeed, there’s growing consensus that erection problems are a risk factor for heart disease, right up there with smoking and high blood pressure.

“The penis is the dipstick of the body’s health,” said Dr. Harry Fisch, director of the Male Reproductive Center at Columbia University Medical Center of New York Presbyterian Hospital. “If you’re able to have sex and healthy erections, it’s a good sign that your cardiovascular system is in good shape. If you can’t, it’s time to see your doctor.”

Impotence — or erectile dysfunction, as it’s sometimes called — was once deemed chiefly a psychological problem. When it occurs in men in their 20s and 30s, it often is. “But especially when men hit middle age, the main cause of erectile dysfunction is almost always vascular,” said Dr. Laurence Levine, professor of urology at Rush University Medical Center in Chicago. The same factors that can clog up arteries and lead to heart attacks and strokes — smoking, elevated cholesterol, inflammation and high blood pressure — also wreak havoc on the blood vessels that supply the penis. A flagging erection may be one of the earliest warning signs of trouble.

“The arteries in the penis are about one-third the size of one of the coronary arteries supplying the heart,” Dr. Levine explained. “When smaller blood vessels, such as the penile arteries, are compromised even a small amount, it can have a major effect on their capacity to dilate. And that will show up as a noticeable difference in the quality of an erection.”

When a man becomes aroused, the brain sends signals to the penis to release a chemical that rapidly widens blood vessels. Blood rushes in, causing an erection. Damage to those vessels can make them inflexible, limiting their ability to expand. When the damage gets bad enough, the spirit may be willing but the flesh unable.

Since men are all too aware when their erections begin to flag, erectile dysfunction may serve as a useful early warning sign of cardiovascular problems. In a British study that compared 207 men with heart disease with 165 healthy controls, investigators at Buckinghamshire Chilterns University College found that erectile woes can precede such problems as a heart attack or angina by up to five years.

“What you really worry about is the guy who goes online and gets Viagra, never knowing that the reason he’s having problems is that he’s got very high cholesterol levels and is diabetic,” said Dr. Wayne J. Hellstrom, professor of urology at Tulane University School of Medicine in New Orleans and co-author of a 2007 study that found that the more risk factors a man has for coronary artery disease, the greater his odds of having abnormal blood flow in his penis. The poorest blood flow showed up in men who already had coronary artery disease and diabetes.

To complicate matters, certain prescription drugs — including some high-blood-pressure medicines, cholesterol-lowering drugs, antidepressants and tranquilizers — can cause or worsen erection problems. “Twenty-five percent of erectile dysfunction may be related to medications,” said Dr. Kevin T. McVary, professor of urology at the Feinberg School of Medicine at Northwestern University in Chicago. Sometimes doctors can switch patients to a similar drug that doesn’t cause problems. But not always. “In that case we have to treat around the side effect, usually by prescribing a drug like Viagra,” Dr. McVary said.

In some men, getting high blood pressure and cholesterol under control, along with stepping up physical activity and shedding a few pounds, may be enough to improve erections. After participating in a program to lose weight and get more exercise, for example, one group of 55 obese men studied at the University of Naples in Italy significantly bettered their scores on a test called the International Index of Erectile Function.

Studies have shown that a diet abundant in fruits, vegetables, whole grains and fish, like that traditionally eaten in the Mediterranean region, may also help by reducing vascular inflammation. If a healthier diet means losing weight, all the better. “People with huge pot bellies typically have very low testosterone, the male hormone,” Dr. Fisch explained. “Visceral fat eats up testosterone. When men lose belly fat, their testosterone goes up.” So does their libido and, in some cases, the most obvious manifestation of it. Exercise is also important, he said, because it helps open up blood vessels.

Of course, diet and exercise are a tough sell when a simple pill can do the trick quickly. Treatment of impotence has undergone a revolution with the advent of Viagra and two similar drugs, Levitra and Cialis. All three work by blocking the breakdown of the chemical that causes blood vessels in the penis to widen. That in turn allows more of the chemical to build up, bolstering an erection.

Despite the happy images of smiling silver-haired couples in the ads, however, erectile dysfunction medications may not work for everyone. If blood vessels become too damaged, they can’t widen sufficiently. “As many as 30 percent of the men we see don’t get much improvement using these drugs,” Dr. Levine said. For some of them, exercise and weight loss may increase the pills’ effectiveness, as may lowering elevated cholesterol levels with cholesterol-lowering statin drugs.

The findings underscore the importance that men 40 and older see a doctor and treat cardiovascular risk factors if erection problems arise.

As for younger men, the latest findings are even more encouraging. Heeding the familiar advice to maintain a normal weight, get plenty of exercise and avoid smoking could well ensure sturdier erections for years to come. That’s potent motivation by any measure.