“The trajectory over time is remarkable,” said Dr. Marc Schuckit, a psychiatrist and addiction specialist at the University of California, San Diego, who wrote an editorial accompanying the new report. “You have to say there’s something going on.”

Even if the rate of alcohol problems among older people doesn’t climb further, the sheer numbers will increase. “The growth in that population portends problems down the road,” said Bridget Grant, an epidemiologist at N.I.A.A.A. and the lead author of the study.

Why this spike in late-life drinking? Dr. Grant’s team didn’t investigate causes, but she speculates that anxiety caused by the recession, which hit right between the two surveys, may have played a part.

Other experts point to demographic differences. People in their 60s and early 70s are less frail than in previous generations — so they continue their drinking patterns. Moreover, baby boomers have been more exposed to, and are less disapproving of, drug and alcohol use.

“It’s a lot more acceptable,” said Dr. David Oslin, a psychiatrist specializing in addiction at the University of Pennsylvania. “We no longer have those folks who grew up with Prohibition, with abstinence as a value.”

Even if older people are healthier, they’re still prone to late-life physical changes that make drinking riskier. While two drinks a night at age 40 might not be an issue, two daily drinks at 70 is more complicated.

With each drink, an older person’s blood alcohol levels will rise higher than a younger drinker’s, Dr. Schuckit noted; older people have less muscle mass, and the liver metabolizes alcohol more slowly. Aging brains grow more sensitive to its sedative properties, too.