Cheerful people walk more quickly and are more active in as they age than unhappy people, said researchers from University College London (UCL).
The study of 3,199 men and women aged 60 years or over living in England looked at the link between positive well-being and physical well-being, following participants over 8 years.
"The study shows that older people who are happier and enjoy life more show slower declines in physical function as they age," said Dr Andrew Steptoe from UCL.
"They are less likely to develop impairments in activities of daily living such as dressing or getting in or out of bed, and their walking speed declines at a slower rate than those who enjoy life less," Steptoe said.
Researchers assessed participants' enjoyment of life with a four-point scale, rating the following questions: "I enjoy the things that I do," "I enjoy being in the company of others," "On balance, I look back on my life with a sense of happiness" and "I feel full of energy these days."
They used personal interviews to determine whether participants had impairments in daily activities such as getting out of bed, getting dressed, bathing or showering. They gauged walking speed with a gait test.
Participants in the 60-69-year bracket had higher levels of well-being as did those with higher socioeconomic status and education and those who were married and working.
People with low well-being were more than three times as likely as their positive counterparts to develop problems in their daily physical activities.
"This is not because the happier people are in better health, or younger, or richer, or have more healthy lifestyles at the outset, since even when we take these factors into account, the relationship persists," Steptoe said.
"Our previous work has shown that older people with greater enjoyment of life are more likely to survive over the next 8 years; what this study shows is that they also keep up better physical function," he said.
The study was published in the Canadian Medical Association Journal.