A landmark study of retirement community residents who lived past 90 is providing a guide that could help.

They’re called “the oldest old.” They are people age 90 and above, and they are the fastest-growing segment of the U.S. population. Now a landmark study of thousands of members of a retirement community in Southern California is revealing factors that may contribute to living longer. Some of the findings are no surprise — smoking led to shorter lifespans, while those who exercised lived longer. Other findings were unexpected — vitamins did not prolong life, but carrying some extra weight did.

Lesley Stahl went to Laguna Woods, Calif., to report on this study and its remarkably spry subjects for 60 Minutes, Sunday, May 4 at 7 p.m. ET/PT.

Dr. Claudia Kawas of the University of California, Irvine, found the research equivalent of a gold mine when she discovered that 14,000 residents of a retirement community formerly known as “Leisure World” (now Laguna Woods) had filled out detailed questionnaires about their diet, activities, vitamin intake, and medical history back in the early 1980s. With $6 million from the National Institutes of Health, she and her staff took those 14,000 files and began a research project called “90+.” Who had died and when? Who was still alive and over 90? They were able to locate and sign up 1,600 of those 90-plussers, as they call them, many still living at Laguna Woods. Each is examined physically and cognitively every six months.

“People who exercised definitely lived longer than people who didn’t exercise. As little as 15 minutes a day on average made a difference,” says Dr. Kawas. Keeping active in non-physical ways, such as socializing, playing board games, and attending book clubs, also was associated with longer life. “For every hour you spent doing activities in 1981, you increased your longevity, and the benefit of those things never leveled off,” she tells Stahl.

Kawas tells Stahl that being obese at any age is unhealthy. However, she found that older people who were moderately overweight or average weight lived longer than people who were underweight. “It’s not good to be skinny when you’re old,” Dr. Kawas says.

Vitamins didn’t seem to affect longevity, but alcohol intake did, with people who drank up to two drinks per day having a 10-15 percent reduced risk of death compared to non-drinkers. “A lot of people like to say it’s only red wine. In our hands it didn’t seem to matter,” says Dr. Kawas.

One of the biggest surprises so far in the study is that 40 percent of the time, what seemed to be Alzheimer’s disease in people over 90 actually wasn’t. The researchers learned this by studying the brains of the subjects after death; many showed evidence of microscopic strokes. Kawas says she hasn’t yet figured out what caused the strokes, so she can’t say how to prevent them. She tells Stahl, “I wish I did. But I will soon, I hope.”