The older that seniors feel relative to their actual age, the greater their odds of cognitive decline in the coming years, a recent study finds.

Among nearly 6,000 U.S. seniors followed for two to four years, those who felt older than their years at the start were 18 percent more likely to develop cognitive impairment and 29 percent more likely to develop full-blown dementia, compared with peers who felt younger.

Study participants who were depressed and didn't exercise were more likely to rate themselves as feeling older at the outset, the study authors note in Journals of Gerontology: Psychological Sciences.

That's in line with past research suggesting a link between depression and dementia, Yannick Stephan of the University of Montpellier in France and colleagues wrote.

"If you do things that make you feel young, like exercise, spend time with friends and family, or enjoy a hobby, it could protect you from memory decline," said Eric Vogelsang, a sociology researcher at California State University in San Bernardino who was not involved in the study.

"Basically, it's about healthy living, including having a passion for life," he said.

The study team analyzed data from 5,748 adults in the U.S., ages 65 to 98, who initially had no cognitive problems.

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About half the participants completed a survey in 2008 asking them to specify, in years, how old they felt, and the other half completed it in 2010.

All participants were interviewed and researchers tested their memory and thinking skills to determine whether they had normal cognitive function, so-called cognitive impairment without dementia, or dementia. The same tests were performed at follow-up two to four years later.

The study team also asked participants if they experienced depression symptoms, participated in sports or aerobic activities and whether they had diabetes or a history of smoking.

Only participants with normal cognitive function at the start of the study were included in the analysis. At the follow-up, most still had normal cognitive function, but 979 people (17 percent of the group) were classified as cognitively impaired and 94 people, just under 2 percent, had dementia.

Based on the study results, Vogelsang told Reuters Health, "if an 80-year old feels 85 instead 75, that would increase the odds of getting dementia by about 30 percent."

The authors noted that negative stereotypes about aging may be another the reason why people felt older, suggesting that internalizing these stereotypes could affect cognitive function, thus increasing the risk of dementia.

The researchers accounted for sex, race and age in their analyses, but the study did have some limitations.

"They didn't account for most other health problems other than dementia," Vogelsang said. "For example, they didn't measure for stress or other physiological problems in the study," he added. "One reason that people may feel old is because of stress - and we think stress is related to dementia."

Although feeling young is important, Vogelsang cautioned that it may not always help.

"People may have a premonition for when their mind and body has begun to deteriorate," he said. "If so, then being optimistic can only take them so far."