When young adults see their annual income plummet, more than their bank accounts may suffer: New research suggests their brains may eventually pay the price.
The study found that people in their 20s and 30s who experienced "income volatility" generally performed worse on tests of thinking and memory skills once they hit middle age.
Compared with their peers with more stable incomes, their scores on one set of tests were almost 4 points worse, on average.
Experts stressed that the study does not prove that income fluctuations are to blame. And it's not clear what the ultimate impact on brain health, including dementia risk, might be.
"What this shows is that income volatility in young adulthood is related to how the brain works in middle age," said Dr. Joel Salinas, a neurologist at Harvard Medical School and Massachusetts General Hospital, in Boston. "That gives signals to other researchers that this is something to look at in future studies."
Salinas wrote an editorial published with the findings in the Oct. 2 online edition of Neurology.
A number of studies have found that lifestyle and environment -- from exercise and diet to chronic stress -- may help determine how well the brain ages.
But there are many influences "upstream" of those factors, Salinas said. Things like childhood experiences, education, job opportunities, income and race can all affect whether people face chronic stress, or have a healthy diet, or exercise regularly.
Research has already uncovered links between lower income and problems with memory and thinking skills later in life. The new study focused on income instability, in part, because it's a problem that's becoming more common, according to lead researcher Leslie Grasset.
More than one-third of U.S. households said their income dropped by at least 25 percent between 2014 and 2015.
Plus, there are relatively straightforward ways to address those income fluctuations, said Grasset, a post-doctoral associate at the INSERM Research Center, in Bordeaux, France.
"Unemployment and wage insurance have been implemented as short-term strategies to offset the burdens of income shocks," she said.
Programs like food stamps and the Earned Income Tax Credit, Grasset added, might help families deal with sudden income drops, too.
For the study, Grasset's team analyzed data on nearly 3,300 young U.S. adults who entered a heart-health study in 1990. Twenty years later, the participants completed standard tests of memory, information processing and executive function (the brain's ability to focus, regulate behavior, get organized and achieve goals).
Overall, 399 participants had at least two income drops of 25 percent or more during the study period. Those people typically performed worse on the tests of executive function and processing speed (but not memory), versus participants with no significant income drops.
Why? In theory, highly educated people might enjoy more stable incomes and better brain function. But Grasset said the differences were not explained by education levels.
Nor were the findings solely due to physical health conditions, like high blood pressure, or lifestyle factors such as exercise and smoking.
A key limitation of the study, though, is timing. The researchers do not know whether the poorer mental acuity actually came first -- before any income instability.
"'Reverse causation' cannot be ruled out as an explanation for our results," Grasset said.
Future studies can try to address that question, Salinas said. They could look at repeated measures of mental abilities, and whether they change after periods of income loss.
"Maybe we'll learn that it's income volatility, more than total income, that's important to brain health," Salinas noted.
Why would income stability matter? Chronic stress could be one way, according to Grasset's team. So could disruptions in health care -- including any medications a person may be taking to manage high blood pressure or other chronic conditions that can ultimately affect brain health.