The two go hand-in-hand -- being social can help keep away the blues.
"The good news is that with age comes happiness," said study author Yang Yang, a University of Chicago sociologist. "Life gets better in one's perception as one ages."
A certain amount of distress in old age is inevitable, including aches, pains and deaths of loved ones and friends. But older people generally have learned to be more content with what they have than younger adults, Yang said.
This is partly because older people have learned to lower their expectations and accept their achievements, said Duke University aging expert Linda George. An older person may realize "it's fine that I was a schoolteacher and not a Nobel prize winner."
George, who was not involved in the new study, believes the research is important because the general public continues to think that "late life is far from the best stage of life and they don't look forward to it."
Yang's findings are based on periodic face-to-face interviews with a nationally representative sample of Americans from 1972 to 2004. About 28,000 people aged 18 to 88 took part.
There were ups and downs in overall happiness levels during the study, generally corresponding with good and bad economic times. But at every stage, older Americans were the happiest.
While younger blacks and poor people tended to be less happy than whites and wealthier people, those differences faded as people aged.
In general, the odds of being happy increased 5 percent with every 10 years of age.
Overall, about 33 percent of Americans reported being very happy at age 88, versus about 24 percent of those age 18 to their early 20s. And throughout the study years, most Americans reported being very happy or pretty happy; less than 20 percent said they were not too happy.
A separate University of Chicago study found that about 75 percent of people aged 57 to 85 engage in one or more social activities at least every week. Those include socializing with neighbors, attending religious services, volunteering or going to group meetings.
Those in their 80s were twice as likely as those in their 50s to do at least one of these activities.
Both studies appear in April's American Sociological Review.
"People's social circles do tend to shrink a little as they age -- that is mainly where that stereotype comes from, but that image of the isolated elderly really falls apart when we broaden our definition of what social connection is," said study co-author Benjamin Cornwell, also a University of Chicago researcher.
The research rings true for 81-year-old George O'Hare, a retired Sears manager in Willowbrook, Ill. He's active with church, AARP and does motivational speaking, too. His wife is still living, and he's close to his three sons and four grandchildren.
"I'm very happy because I've made friends that are still living," O'Hare said. "I like to go out and speak in schools about motivation."
"Happiness is getting out and being with people, and that's why I recommend it," he said.
Ilse Siegler, an 84-year-old retired nurse manager in Chicago, has a slightly different perspective. Her husband died 35 years ago; she still misses him everyday.
She has vision problems and has slowed down with age. Yet, she still swims, runs a social group in her condo building, volunteers in a retirement home and is active with her temple. These all help "make life more enjoyable," she said.
While Siegler said these aren't the happiest years of her life, she's content.
"Contentment as far as I'm concerned comes with old age ... because you accept things the way they are," she said. "You know that nothing is perfect."
Cornwell's nationally representative study was based on in-home interviews with 3,005 people in 2005-06. While it didn't include nursing home residents, only about 4 percent of Americans aged 75 to 84 are in nursing homes, Cornwell said.
It's all good news for the aging population. However, Yang's study also found that baby boomers were the least happy. They could end up living the unfortunate old-age stereotype if they can't let go of their achievement-driven mind-set, said George, the Duke aging expert.
So far, baby boomers aren't lowering their aspirations at the same rate earlier generations did. "They still seem to believe that they should have it all," George said. "They're still thinking about having a retirement that's going to let them do everything they haven't done yet."
Previous research also has shown that mid-life tends to be the most stressful time, said Cornell University sociologist Elaine Wethington. "Everyone's asking you to do things and you have a lot to do. You're less happy because you feel hassled."
The new studies show "if you can make it through that," there's light at the end of the tunnel, Wethington said.