Image caption Those in poverty may need extra help with the tasks of daily life, say the researchers

Being poor can sap a person's mental resources, research published in the journal Science suggests.

The work, by an international team, demonstrates how poverty takes its toll on cognitive function, leaving less mental capacity for other tasks.

The evidence comes from two studies carried out in India and the US.

Previous data had shown a link between poverty and bad decision-making, but the root causes of this correlation were unclear.

The US, British and Canadian team tried to shed light on this chicken-and-egg puzzle by isolating the financial factor from others that might interfere with the results.

One part of study used the natural financial cycle (tied to the crop cycle) of sugarcane farmers in India.

The farmers go through three crucial stages in this cycle; before the harvest, when they have taken out loans to grow the crops and thus are extremely poor; after the harvest, but before being paid, when farmers are at the greatest extent of their poverty; and after being paid.

Varying ability

Dr Anandi Mani, from the Centre for Competitive Advantage in the Global Economy (Cage) at the University of Warwick, UK, set the farmers cognitive tests at each stage of the cycle and found that mental acuity varied with their income.

"With the sugarcane farmers, we are comparing the same person when he has less money to when he has more money. We're finding that when he has more money he is more intelligent, as defined by IQ tests," said Dr Mani.

The study aimed to rule out other confounding factors like nutrition, health, physical exhaustion and family commitments.

The researchers also tried to limit the influence of factors related to stress by measuring biomarkers such as blood pressure and heart rate.

To make sure the findings were not in some way unique to Indian sugarcane farmers, a control study was completed in the US.

Using two groups of people, one wealthy, one poor, they triggered thoughts about their personal financial situations using easy and difficult hypothetical questions, and then got them to sit non-verbal tests.

"What we find there is when it is the easy condition there is no difference in performance of the rich or poor. But in the harder condition, that's when the performance of the poor drops off a lot," Dr Mani said.

Extra support

The study concludes that those in poverty, by having more constant and extensive financial worries, expend more of their mental capacity on these concerns, so that less can be used for other tasks.

"The findings that we have are about the immediate impact of poverty: the fact that I am dealing with 'putting out fires' now. This is an immediate impact," said Dr Mani.

Dr Mani suggests that greater support needs to be given to those in poverty to help them with the tasks of daily life. She also suggests that our perceptions of the poor need to change.

Prof Kathleen Vohs, behavioural scientist at the University of Minnesota, welcomed the findings.

"It's impressive work. I think it will move the conversation about poverty forward. This is the first time that a causal relationship has been provided between poverty and bad decision-making," she said.

The results indicate that the constant financial pressure can initiate a downward spiral for the less fortunate in society.

"Hopefully it will make others view [those in poverty] more empathetically, as this feature [of making bad decisions] exists in all of us, but is just more prominent in the poor," said Prof Vohs.