"Income is dynamic and individuals are likely to experience income changes and mobility especially between young adulthood and midlife," said lead investigator Adina Zeki Al Hazzouri from University of Miami.
"The study places economic hardship as the pathway to cognitive ageing and as an important contributor to premature ageing among economically disadvantaged populations," Hazzouri added.
The researchers found strong and graded associations between exposure to economic hardship and worse cognitive function, especially in processing speed.
In the study, individuals with all-time poverty performed significantly worse than individuals never in poverty.
Similar results were observed in persons with perceived financial difficulty, the reseachers said.
Previous research has shown that exposure to poor socio-economic conditions during childhood, adulthood or cumulatively is associated with cognitive deficits.
However, most of these studies involved older adults and so there is little data on whether economic adversity influences cognitive health much earlier in a person's life.
For the new study, the team examined the effects of sustained poverty and perceived financial difficulty on cognitive function in midlife using income data for about 3,400 adults in US, aged between 18 to 30, at the start of the study in 1985-86.
Sustained poverty was defined as the percentage of time the participants' household income was less than 200 per cent of the federal poverty level.
Participants were divided into four groups: never in poverty, less than one-third of the time, from one-third to nearly 100 per cent of the time, or always in poverty.
In 2010, at a mean age of 50 years, participants underwent three tests that are considered reliable to detect cognitive ageing.
"It is important to monitor how trends in income and other social and economic parameters influence health outcomes," Hazzouri said in a paper published in the American Journal of Preventive Medicine.
