People think of aging as a steady decline, with seniors gradually losing their physical abilities and mental agility as the years wear on.

But a new study suggests that seniors can – and often do – improve over time, with the right mindset.

Nearly half of seniors 65 and older showed measurable improvement in their brain health, physical function or both over time, researchers reported in the journal Geriatrics.

“Many people equate aging with an inevitable and continuous loss of physical and cognitive abilities,” lead researcher Becca Levy, a professor of social and behavioral sciences at the Yale School of Public Health, said in a news release.

“What we found is that improvement in later life is not rare, it’s common, and it should be included in our understanding of the aging process,” Levy said.

For the new study, researchers tracked more than 11,000 people participating in a long-term federally funded study of older Americans.

During a follow-up period of up to 12 years, 45% of participants improved in either physical or mental fitness, results show.

About 32% had improvements in their brain health, and 28% improved physically, researchers found.

“What’s striking is that these gains disappear when you only look at averages,” Levy said. “If you average everyone together, you see decline. But when you look at individual trajectories, you uncover a very different story. A meaningful percentage of the older participants that we studied got better.”

The study also found that people with more positive beliefs about aging were significantly more likely to show improvements in both their brain power and their walking speed, even after accounting for other factors.

Seniors who showed improvements weren’t just recovering after being sick or injured, either. A substantial proportion of participants who were healthy at the start of the study improved mentally or physically over time, results show.

“Our findings suggest there is often a reserve capacity for improvement in later life,” Levy said. “And because age beliefs are modifiable, this opens the door to interventions at both the individual and societal level.”

These findings fit into a theory of Levy’s that holds that negative age stereotypes, absorbed from the culture, can wind up having an impact on how healthy a person ages.

Previous studies have found that negative aging beliefs predict poorer memory, slower walking speed, higher heart risk, and potentially increased risk of Alzheimer’s disease.

Researchers said these results should encourage preventive care, rehabilitation and health-promoting programs for seniors that draw on their potential resilience.