Falling into poverty appears to make people become less intelligent and become old before their time, according to a new study.

Researchers found life on the breadline for 20 years was “strongly associated” with “worse cognitive function” and premature aging.

And they suggested the potential causes of this phenomenon included the stress of having little money, inadequate housing and sanitation, and an unhealthy lifestyle – a poor diet, smoking, alcohol and too little exercise.

Writing in the American Journal of Preventative Medicine, researchers led by Professor Adina Zeki Al Hazzouri, of Miami University, said the trend was found even among highly educated people who fell on hard times.

This, they argued, means it is unlikely that people who are becoming less intelligent for some other reason are falling into poverty.

The researchers studied information about 3,400 adults who took part in a study on heart disease. They were all 18 to 30 when the project began in 1985.

As part of that study, details about their income were recorded and they were also given tests used to detect what is known as “cognitive aging”.

What the researchers found was that people who lived continually in poverty “performed significantly worse” than those who had never had to survive on a low income in tests of verbal memory, the brain’s processing speed and its executive function.

“The overall magnitude of the associations suggests that economic adversities experienced in young adulthood are important determinants of cognitive health in midlife,” the paper said.

“From a mechanistic perspective, economic hardship may be on the pathway and an important contributor to clinically significant cognitive deficit and premature aging among economically disadvantaged individuals.

“Furthermore, in analyses restricted to participants with a high level of education, significant associations were still observed, suggesting little evidence that reverse causation could explain these findings.”

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They put forward four different possible “pathways” in which poverty could affect people’s brains.

“First, exposure to low income and socioeconomic conditions has been associated with unhealthy behaviours, such as alcohol use, smoking, and inadequate physical activity, which are in turn risk factors for small brain infarcts and poor cognition,” the paper said.

“Second, exposure to low income may influence educational attainment and ultimately shape many of the risk factors of cognition, including adult living environment (inadequate housing and sanitation), health behaviours, and access to resources.

“Third, the stress of exposure to low income has been shown to be associated with dysfunction of the hypothalamic adrenocortical axis [glands inside the brain], which in turn is a pathway leading to worse risk factors of cognition.