Article In Brief
In a population-based study, researchers reported that higher income volatility and subsequent income drops among young adults were, in fact, associated with a significant worsening of processing speed and executive functioning, as well as worse microstructural integrity of total brain and total white matter findings on MRI.
To what extent does economic instability impact brain health? That question is at the heart of a new analysis that found that fluctuations in income and economic instability were not only associated with adverse health outcomes, they also affected cognitive abilities over time.
Previous studies have linked low socioeconomic status with poor health consequences—some have reported associations between income volatility and cardiovascular and mental health, said Leslie Grasset, PhD, a postdoctoral associate at the Inserm Research Center in Bordeaux, France, and the lead author of the paper published in the October 2 online edition of Neurology. Yet few studies have explored how economic instability and dramatic changes in household income affect cognition in the long term.
“Income volatility has been on the rise since the 1980s, yet previous studies have examined this relationship between income and cognitive health at one or maybe two time points,” Dr. Grosset told Neurology Today.
She and her colleagues decided to look more specifically at the relationship between brain aging and fluctuations in income by pulling data from the Coronary Artery Risk Development in Young Adults study (CARDIA), an ongoing prospective study of cardiovascular disease and its risk factors in young to middle-aged adults.
“Income volatility has been on the rise since the 1980s, yet previous studies have examined this relationship between income and cognitive health at one or maybe two time points.”
—DR. LESLIE GRASSET
The CARDIA team collected data on self-reported pretax income of 3,287 young adults between the ages of 20 and 35 at six different points from 1990 through 2010; in 2010, they administered a battery of tests to assess verbal memory and word retrieval; processing speed; and executive functioning.
The researchers found that higher income volatility and subsequent income drops were, in fact, associated with a significant worsening of processing speed and executive functioning, as well as worse microstructural integrity of total brain and total white matter findings on MRI. [See “The CARDIA Study: Findings on Brain Health” for more specific data.”]
Although the study is observational and does not prove causation, Dr. Grasset said, “Our results do suggest that large fluctuations in income across early adulthood may be detrimental for cognitive function and brain integrity in midlife. Importantly, the CARDIA study provides an adequate setting to investigate income volatility, enabling us to assess income over two decades of these participants' lives, at an age where most adults are in the workforce.”
“Overall, income volatility and disadvantaged socioeconomic conditions may increase exposure to several risk factors of poor brain health,” Dr. 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 health care, which may result in worse management of these risk factors and potentiate their impact on brain health.”
The next step, she said, would be to study the mechanism behind this relationship. For example, “the investigation of subsequent cognitive decline and changes in brain structures in older ages, as well as the factors involved in these evolutions, could help with this matter.” Future studies examining the effect of social policies aimed at mitigating the impact of unpredictable income changes on brain aging are needed, she said.
What Do the Findings Mean for Care?
Neurologists and health services researchers who were not involved with the study said the findings were sobering.
Martha J. Farah, PhD, director of the Center for Neuroscience & Society at the University of Pennsylvania, told Neurology Today that the finding “that financial strain is not conducive to good cognitive ability or brain health,” does not come as a surprise. “
But, she said, “This study takes us beyond that fairly obvious conclusion in two ways. First, it shows that income volatility per se, above and beyond total earnings, seems to impact key cognitive abilities and measures of brain health. Second, the magnitudes of these effects are impressive—scary even! The magnitude of socioeconomic influences is in the same ballpark as the influences we see from genes, toxins, and other ‘biological’ factors.”
Dr. Farah noted that the underlying mechanisms linking socioeconomic factors to brain health remain unclear. “Learning how income volatility ‘gets into the head’ is an important challenge for neuroscience given its public health relevance, not to mention the profound basic science questions of how social context shapes our biology,” she said.
“This study provides an interesting view into the effects of socioeconomic disparities on the health care system,” Oscar L. Lopez, MD, FAAN, professor of neurology and psychiatry, Levidow-Pittsburgh Foundation endowed chair in Alzheimer's disease and related dementias, director of the Alzheimer's Disease Research Center at University of Pittsburgh School of Medicine, agreed. Specifically, it was novel “that during an observation period of approximately 20 years, individuals with higher income volatility and income drops had worse cognitive performance than those without those features.”
Practically speaking, what, if anything, do these data mean for neurology? In an editorial accompanying the Neurology study, Joel Salinas, MD, MBA, MSc, a neurologist at Harvard Medical School and Massachusetts General Hospital, called for increased emphasis on efforts to address social disparities and their impact on brain health. Dr. Salinas suggested studies like this one are a reminder of the moral responsibility neurology has to treat “social ills.”
“In an era plagued by a cycle of rising socioeconomic inequality, widening health disparities, and dwindling lifelong earning potential, times of individual and societal instability have tremendous and enduring consequences,” he wrote. “If neurology's earnest mission is to save lives and preserve our patients' capacity to think, feel, and thrive, then cultivating a virtuous cycle between social health and brain health is our clinical and humanitarian duty.”
Dr. Lopez said he agreed with Dr. Salinas' argument and the editorial's conclusions—that neurologists need to be aware of the “‘virtuous cycle between social health and brain health’ that is present through the lifespan of our patients.” While neurologists cannot modify the socioeconomic status of their patients, they will have to deal with the long-term consequences of these problems.
“It is possible that job volatility and income were, most likely, related to periods of employment, which led to the loss of health insurance, and limited the access to preventive treatments during critical periods of time, especially in those with risk factors for cerebrovascular disease (for example, hypertension, diabetes),” Dr. Lopez said.
In addition to socioeconomic causes, many other factors can explain the results of this study, he continued. “For example, practically half of the population that had both higher income volatility and income drops had less than 12 years of education and were more likely to be a current smoker and had more obesity at baseline—all these factors have been associated with increased incidence of cardiovascular and cerebrovascular disease. This group is also at risk of increased prevalence of psychiatric illness and substance abuse, which are also determinants of multiple systemic and neurological diseases.”
Although more research is needed to decipher and translate these outcomes into action, there are already implications, the commentators agreed. Moving forward, it will be critically important to incorporate these findings about social determinants of brain structure and functioning in adults into the design of preventive policies in the population, Dr. Lopez said.
The societal impact of reduced brain health and cognitive ability must also be factored in “when weighing the costs to society of employment programs and such,” Dr. Farah added. The study authors pointed out that the focus on income volatility was of particular significance because of “straightforward policy options” including unemployment insurance and other short-term income supports.
Ultimately, “neurology must build on prior efforts and studies like the present one to contribute collectively toward a more robust population brain health approach, targeting fundamental determinants of disease with fundamental interventions. We must connect to a greater extent neurology's clinical practice with public good,” Dr. Salinas wrote in the Neurology editorial; he proposed provider toolkits and targeted interventions as a few action items to incorporate in this process.
The CARDIA Study: Findings on Brain Health
The CARDIA analysis included 3,287 participants from field centers in Birmingham, AL; Chicago; Minneapolis, and Oakland, CA, who were between the ages of 23 and 35 in 1990 when they were assessed for the CARDIA prospective cohort study. At six time points (1990, 1992, 1995, 2000, 2005, and 2010), participants self-reported their pretax household annual income. The researchers only included participants with at least three measures of income in the analysis.
In 2010, participants were given cognitive tests to measure verbal memory and word retrieval; processing speed; and executive functioning.
After adjusting for covariates, the investigators found that the greater the number of income swings, the worse the participants performed on tests of processing speed (β = −1.09, 95% confidence interval [CI] −1.73 to −0.44) and executive functioning (β = 2.53, 95% CI 0.60-4.50) tests. Income swings did not significantly affect verbal memory, however.
Individuals who had two or more income drops had smaller total brain volume (β = −0.88, 95% CI −1.53 to −0.23) compared with those with no changes in income, Dr. Grasset and colleagues reported. In general, higher income volatility was associated with lower total microstructural brain integrity and white matter fractional anisotropy (FA) on imaging scans.
Two or more income drops were also associated with lower total brain FA and lower white matter FA when compared with no income changes.
Even after adjusting for potential confounders, “including socioeconomic, behavioral, and cardiovascular risk factors, which could potentially interfere in the relation between income volatility and cognition,” the investigators noted that these links were “robust.”
The main limitations of the analysis included the inability to rule out reverse causation and the fact that participants reported income according to preset brackets and exact numbers could not be verified, according to Dr. Grasset.
This study was funded by grants from the National Institutes of Health and National Institute on Aging (NIA); CARDIA is supported by the National Heart, Lung, and Blood Institute and the NIA.