Sustained periods of poverty don't just make people sick, they also reduce their capacity to think clearly and remember. Even seeing yourself as struggling financially, irrespective of actual income, can be associated with loss of brain function. In an era where an ever-increasing proportion of jobs rely more on intellectual than physical attributes, this could be the ultimate poverty trap.
A paper in the American Journal of Preventative Medicine measured the effect of spending part or all of a person's adult life with an income less than double the US federal poverty line. Long periods with little money were associated with large decreases in performance on three standard measures of cognitive function. Not surprisingly, things got worse the longer people spent being poor.
The association between poverty and ill-health is backed up by a mountain of studies. However, first author Dr Adina Hazzouri of the University of Miami points out that most research on the topic has looked only at a snapshot in time, rather than considering how people's income varied over their lives. Moreover, the research that has been done on poverty and brain function focused on older people's susceptibility to dementia.
Hazzouri set out to correct this using a study that began for a different purpose, as part of a long-term investigation into the risk of coronary artery disease in young adults. Over the period 1985 to 2010, a group of more than 5,000 people, born on average in 1960, were tracked intensively, with the results providing a rich source of study for researchers on many topics. By 2010, many had dropped out or died, but the 3,383 taking part in the tests for brain function at the end were more than sufficient to observe statistically significant effects.
On a 15-point test for verbal memory, people who had spent the entire 25 years with low incomes scored 2.4 points lower, on average, than those who had never been poor. Those who had been poor for at least a third of their adult life were more than 25 percent slower when challenged to spell out words at speed.
People who described themselves as having faced financial difficulties, whether or not they met objective tests for poverty, suffered a smaller, but still significant, loss of capacity.
Exactly how poverty triggers these effects is unclear. Hazzouri offers four possible explanations, including reduced opportunities for education, higher propensity for smoking and inadequate physical activity, the hormonal effects of stress, and the inferior health infrastructure available to the poor in most places.
Critics might argue that the paper confuses cause and effect, with less intelligent people being more likely to spend time in poverty, but Hazzouri and her co-authors attempted to test for this possibility. They found that even highly educated participants in the test scored worse on the brain function tests if they'd spent a lot of their life poor. This, they argue, demonstrates poverty can cause declines in intellectual capacity, rather than being simply an outcome of lower initial cognitive performance.