Young adults who experience a drop in income experience poorer cognitive performance and exhibit lower brain volume on imaging in midlife, results of a large exploratory study show.
Investigators found individuals who experienced at least one income decrease of 25% or more in annual income had significantly poorer performance on cognitive testing compared with their counterparts with stable annual incomes.
“Large fluctuations in income across early adulthood may be deleterious for cognitive function and brain integrity in midlife,” lead study author Leslie Grasset, PhD, postdoctoral associate at the Inserm Research Center, University of Bordeaux, France, told Medscape Medical News.
The study was published online October 2 in Neurology.
Income changes, known as income volatility, are becoming more frequent in the United States, reaching record levels since the 1980s the investigators note. Between 2014 and 2015, more than one third of US households experienced a 25% or greater change in income.
Most of the previous research examining potential cognitive health outcomes and lower socioeconomic status focused on older individuals so “its association with cognitive health earlier in the life course remains relatively unexplored.”
To address this research gap, investigators assessed income volatility between 1990 and 2010 among 3287 participants in the prospective, ongoing multicenter Coronary Artery Risk Development in Young Adults (CARDIA) study.
Participants included black and white men and women 18 to 30 years old at enrollment in 1985 to 1986 who reported pretax income from all sources within certain brackets.
The researchers compared cognitive function test results and magnetic resonance imaging (MRI) findings in 2010 with earlier income volatility in terms of percent change standard deviation and the number of income drops of 25% or more.
“In general, participants with more income drops were more likely to be black, less educated, unmarried, and smokers, and with lower income and unemployed at baseline,” the researchers note.
“Those with more income drops also had more elevated depressive symptoms, had higher mean BMI and systolic blood pressure and were less physically active.”
Results showed that each one standard deviation difference in higher income volatility was associated with worse performance on the Digit Symbol Substitution Test (DSST) and the Stroop test in multiple analyses adjusted for possible confounders.
Furthermore, in fully adjusted models, having one or more income drop of 25% or greater likewise was associated with worse performance on the DSST (one drop: β = −1.74; 95% confidence interval [CI], −2.87 to −0.61; two or more drops: β = −3.74; 95% CI, −5.35 to −2.12), compared with participants reporting no such decreases in income.
In addition, reporting two or more income drops was associated with worse scores on the Stroop test (β = 8.04; 95% CI, 2.94 – 13.31).
Interestingly, there was no link between income volatility and performance on the Rey Auditory Verbal Learning Test (RAVLT).
“We did not find an association between income volatility and verbal memory, likely due to the relatively young age of this cohort,” the researchers note.
Volatility and Brain Volume
The researchers also examined brain volume and microstructural integrity findings among 719 participants in the CARDIA Brain MRI Ancillary Study in 2010.
Compared with participants reporting no major income drops, experiencing two or more income drops was associated with having smaller total brain volume (β = −0.88; 95% CI, −1.53 to −0.23) in fully adjusted models.
In addition, this number of income drops was associated with smaller white matter volume, but only in a minimally adjusted model (β =−0.44; 95% CI, −0.84 to −0.03). This association became nonsignificant in further adjusted models.
The number of income drops was not associated with gray matter volume or hippocampal volume. Likewise, income volatility measured in terms of one standard deviation higher was not associated with MRI volumes.
Grasset and colleagues also examined microstructural brain integrity measured as fractional anisotropy (FA) on MRI. FA is a measure of how uniformly water diffuses within the brain.
They report that each standard deviation more of higher income volatility was associated with lower total brain FA (β = −0.75; 95% CI, −1.29 to −0.18) and lower white matter FA (β = −0.003; 95% CI, −0.005 to −0.0009).
At the same time, compared with no income drops, reporting two or more income drops was associated with lower total brain FA (β = −1.59; 95% CI, −2.96 to −0.20) and lower white matter FA (β = −0.008; 95% CI, −0.01 to −0.003).
In contrast, higher income volatility measured by standard deviations and number of income drops were not associated with gray matter and hippocampal FA.
Finally, interactions between income volatility and income level were all nonsignificant, the researchers note. “As such, we can say that the relation of income volatility with cognition does not vary according to income level,” the researchers write.
Although the factors driving the associations in the study remain unknown, Grasset and colleagues propose several possible mechanisms.
“Overall, income volatility and disadvantaged socioeconomic conditions may increase exposure to several risk factors of poor brain health,” Grasset said. “Individuals who experience important income fluctuations may be more at risk for cardiovascular risk factors, depression, or perceived stress, which are in turn associated with poor cognitive health.”
“In addition, they may have lower access to high-quality healthcare, which may result in worse management of these risk factors, and potentiate their impact on brain health,” she said.
Additional studies are needed to validate the results, the researchers note.
“A next step of this research would be to better understand the mechanisms involved in the relationship between income volatility and brain health,” Grasset said.
“In addition, future studies examining the role of different social policies intended for mitigating the impact of unpredictable income changes on brain aging are needed,” she added.
In an accompanying editorial, Joel Salinas, MD, MBA, of the Henry and Allison McCance Center for Brain Health, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, writes that although the findings from this exploratory analysis require further validation, they are important.
The study emphasizes, “how specific changes in the socioeconomic environment may negatively affect brain health. This has immediate implications for future social determinants research, evidence-based policy, and — less intuitively — clinical practice,” he added.
“A key message is that an unstable income during a person’s 20s and 30s — formative earning years — may jeopardize a young adult’s future brain structure and function by midlife,” Salinas writes.
The National Institutes of Health, the National Institute on Aging and the National Heart, Lung, and Blood Institute funded the study. Grasset and Salinas have disclosed no relevant financial relationships.