Of nearly 2,000 men aged between 51 and 88, 34% reported moderate to severe erectile dysfunction and they were likely to have a larger waistline.
The study, funded by the National Cancer Institute, the National Heart Lung and Blood Institute and the American Cancer Society, also found that inactive men were more likely to suffer erectile dysfunction than men who exercised for at least 30 minutes a day.
Erectile dysfunction, commonly known as impotence, is a consistent inability to gain or sustain an erection.
Risks confirmed
Mr Jim Bramble, vice-president of the British Association of Urological Surgeons, said: "This confirms scientifically what we already had a strong impression of.
"The risk factors for erectile dysfunction are basically drinking too much, smoking and being overweight. Alcohol is particularly important."
Diabetics were also at risk.
He added: "If you can get somebody to go on a diet, do some exercise and cut out the alcohol for a while, you are probably doing them a good deal, particularly if they don't have severe erectile dysfunction."
Many patients, however, wanted the "quick fix" provided by Viagra.