Participants with more income drops also scored worse on how much time it took to complete some tasks.
Researchers have warned that young adults who experience annual income drops of 25 per cent or more may be more at risk of having thinking problems and reduced brain health in middle age. There may be several explanations as to why an unstable income may have an influence on brain health. People with a lower or unstable income may have reduced access to high-quality health care which may result in worse management of diseases like diabetes, or management of unhealthy behaviours such as smoking and drinking.
"Income volatility is at a record level since the early 1980s and there is growing evidence that it may have pervasive effects on health," said study senior author Adina Zeki Al Hazzouri, assistant professor of epidemiology at Columbia Mailman School of Public Health.
"Our results provide evidence that higher income volatility during peak earning years are associated with worse brain aging in middle age," Ms Hazzouri added.
The study involved 3,287 people who were 23 to 35 years old at the start of the study. Participants reported their annual pre-tax household income every three to five years for 20 years, from 1990 to 2010.
Researchers examined how often income dropped as well as the percentage of change in income between 1990 and 2010 for each participant.
Based on the number of income drops, participants fell into three groups: 1,780 people who did not have an income drop; 1,108 who had one drop of 25 per cent or more from the previous reported income; and 399 people who had two or more such drops.
Participants were given thinking and memory tests that measured how well they completed tasks and how much time it took to complete them.
Researchers found that people with two or more income drops had worse performances in completing tasks than people with no income drops. On average, they scored worse by 3.74 points or 2.8 per cent.
"For reference, this poor performance is greater than what is normally seen due to one year in ageing, which is equivalent to scoring worse by only 0.71 points on average or 0.53 per cent," said first author Leslie Grasset of the Inserm Research Center in Bordeaux, France.
Participants with more income drops also scored worse on how much time it took to complete some tasks.
Of the study group, 707 participants also had brain scans with magnetic resonance imaging (MRI) at the beginning of the study and 20 years later to measure their total brain volume as well as the volumes of various areas of the brain.
Researchers found when compared to people with no income drops, people with two or more income drops had smaller total brain volume.
People with one or more income drops also had reduced connectivity in the brain, meaning there were fewer connections between different areas of the brain.
"While the study does not prove that drops in income cause reduced brain health, it does reinforce the need for additional studies examining the role that social and financial factors play in brain ageing," said researchers in a paper published in the journal Neurology.
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