Poverty may dampen mental function and lead to premature brain aging in some people, a new study suggests.

The research included about 3,400 U.S. adults who were aged 18 to 30 at the start of the study in 1985-1986. The volunteers continued in the study until 2010.

At the end of the study, the participants underwent three standard tests to measure brain functions. The tests measured thinking, memory and processing speed.

The researchers found a strong association between financial struggles and worse mental (cognitive) function, particularly in processing speed. Those who spent the entire study period in poverty did significantly worse on these tests than people who were never in poverty, the study showed.

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The results suggest that poverty may be an important factor in brain aging, according to the study authors. However, this study didn’t prove a cause-and-effect relationship between hard economic times and brain health and aging.

The findings were published in the American Journal of Preventive Medicine.

“Maintaining cognitive abilities is a key component of health,” said lead investigator Adina Zeki Al Hazzouri, from the department of Public Health Sciences at the University of Miami Miller School of Medicine.

But it isn’t always possible to avoid poverty. “Income is dynamic and individuals are likely to experience income changes and mobility especially between young adulthood and midlife,” she said in a journal news release.

Four out of five Americans will live near poverty levels at least once in their lives, according to a recent Associated Press survey cited by the study authors.

“Monitoring changes in income and financial difficulty over an extended period of time and how these influence cognitive health is of great public health interest,” Zeki Al Hazzouri said.