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Poverty can lead to mental illness, and vice-versa, study finds

Researchers investigated a large dataset to unearth the causal link between poverty and some types of mental illness

30th July 2024 about a 4 minute read
“Our findings suggest that the reduction of inequalities could lead to substantial public mental health gain." Mattia Marchi, psychiatrist, University of Modena

There is a causal relationship between mental illness and poverty, according to new research.

The researchers, from the Amsterdam Medical Centre, the University of Edinburgh and the University of Modena, looked at data from more than 500,000 participants in the UK Biobank and the international Psychiatric Genomic Consortium, including 18 genome-wide association studies. (These are studies designed to identify genomic variants associated with a particular trait or disease risk.)

Analysing the data, they found a causal relationship between poverty, ADHD, and schizophrenia. They found both that lower income was causally related to these disorders and also that there was a causal relationship between the disorders and lower income. The findings were published in Nature Human Behavior.

Dr Marco Boks, a psychiatrist at Amsterdam University’s Medical Centre, and the lead investigator said: “This study indicates that certain mental health problems can make a person’s financial situation uncertain. But conversely, we also see that poverty can lead to mental health problems.”

Previous research has shown a correlation between poverty and mental illness, but the direction of the association has always been unclear, particularly because of confounding factors such as stress, housing insecurity and substance use.

Causal relationship between poverty and schizophrenia

In this study, investigators developed a measure of poverty based on household income, occupational income and social deprivation. They then examined the possible causal relationship between poverty and nine mental disorders: attention-deficit hyperactivity disorder (ADHD), anorexia, anxiety disorder, autism spectrum disorder, bipolar disorder, major depressive disorder, obsessive-compulsive disorder, posttraumatic stress disorder and schizophrenia.

They also extended the analyses to potential confounders such as cognitive ability.

Researchers then used the participants’ genetic information using Mendelian randomisation to untangle the relationship. Mendelian randomisation is a method of determining the influence of risk factors on a disease, by measuring the variation of genes that are more common in certain traits.

The team found a causal bidirectional relationship between poverty, ADHD and schizophrenia. They found that lower income was causally related to these disorders, and that there was also a causal relationship in the other direction between the disorders and lower income.

They also found a one-directional causation between poverty and major depressive disorder and an inverse causal relationship between poverty and anorexia – in other words, anorexia was more prevalent among people with higher incomes.

“We were able to capture aspects of poverty shared between the individual, the household, and the area in which one lives. This enabled us to better identify the causal effects of poverty on mental illness,” says David Hill, statistical geneticist at the University of Edinburgh.

The effects of poverty on mental illness were reduced by approximately 30% when investigators adjusted for cognitive ability.

The researchers said, however, that their ability to generalise from the findings was limited, because most of the genetic studies were conducted in populations of European ancestry from high-income countries.

The researchers believe that their findings are important for policymakers tackling poverty and mental illness. By recognising the reciprocal influence between poverty and mental illness, policymakers can develop more effective interventions aimed at breaking the cycle of poverty and mental health problems. “Our findings suggest that the reduction of inequalities could lead to substantial public mental health gain,” said Mattia Marchi, a psychiatrist at the University of Modena and one of the study authors.

Boks said the research “provides robust evidence for the need to also look at social factors such as poverty, when you delve into the development of mental illness.” He added: “There is often confusion about the use of genetic data to investigate the relationship between poverty and mental illness. We emphasise that this does not mean that poverty is genetic. On the contrary, with genetic data, we were able to identify poverty as a modifiable environmental factor for mental health.”

FCC Insight

Researchers have long known that there is a relationship between poverty and some types of mental illness. But it has never been clear whether poverty causes mental illness, or whether experiencing a mental illness leads to people becoming poor. This very large-scale study, involving half a million participants from the UK Biobank, found that in some disorders the relationship works both ways – poverty can lead to ADHD and schizophrenia, but the reverse is also true. However, they also found that poverty was a causal factor in major depressive disorder, but not the other way around. The increase, in the past five years, in rates of mental illness in parallel with increased cost of living, lends support to these findings. This research should give policymakers an incentive to address high rates of mental ill-health by tackling one of the root causes: poverty.