Is City Living a Threat to Your Mental Health?

Living in a city is often stressful. Living in cities can be more stressful than living in rural areas due to higher levels of crime, poverty, isolation, and other environmental stresses. For years studies have consistently linked the risk of developing schizophrenia to urban environments-but researchers are only beginning to understand why this association exists. Addressing the link is increasingly urgent: According to a recent U.N. report, the proportion of people living in cities will rise from 54 percent of the world's population in 2014 to 66 percent by 2050.

In the 1930s, researchers first proposed that schizophrenia could be increased by urban living. Since then many large epidemiological studies have reported an association between the two, primarily in European countries such as Sweden and Denmark. Evidence has shown that the likelihood of getting psychosis from growing up in a city is doubled. Other mental illnesses such as anxiety and depression may also be increased by urban living, according to studies.

Many factors can play a role in how cities affect well-being. However, those with mental disorders may find it easier to settle in cities. Two studies published this month shed new light on these effects and suggest both scenarios could be involved.

Growing up in the urban jungle Although the majority of investigations have focused on adults, studies suggest that exposure to urban environments early in life-being born or growing up in a city-matters most. To look more closely at this critical stage of life, a group of researchers led by Helen Fisher, a psychologist at King's College London, and Candice Odgers, a psychologist at Duke University, conducted a longitudinal study involving 2,232 twin children in the United Kingdom.

Neighborhood surveys were used by the researchers to establish whether twins lived either in rural or urban environments between the ages of five and twelve. The researchers used neighborhood surveys to determine whether twins lived in urban or rural environments at ages five and twelve. The researchers also used geodemographic data to assess these communities, and interviewed mothers as well as neighbors. They also conducted in-depth interviews of 12 year olds to assess their psychotic symptoms. This was done in order to find out if they experienced delusions or hallucinations.

According to their analysis, the probability of having psychotic symptoms in 12 years old was almost doubled by growing up within a large city. The most risk factors for developing schizophrenia were exposure to crime and low social cohesion. Although most kids who have psychotic symptoms will not develop schizophrenia as adults, Fisher notes, "In some of the other studies where we follow people later in life, we show that [psychotic symptoms] are actually related to lots of other [mental health] problems as well, so it's a broader marker for that." These problems include depression, post-traumatic stress disorder and substance abuse.

"This [study] adds to our own experimental evidence that strongly leads us to suspect that being in the city does something to a specific circuit in the brain that impairs your ability to deal with social stress," says Andreas Meyer-Lindenberg, director of University of Heidelberg's Central Institute for Mental Health in Germany. Meyer-Lindenberg's research previously showed that those who grew up or lived in cities had stronger activation of the amygdala (brain regions involved in processing emotion and regulation) than people from rural areas. They also discovered similar brain functions in people who moved from rural areas, which is a well-known risk factor for schizophrenia.

It is not common for people to live in urban areas. Epidemiological studies provide strong evidence that an urban upbringing could contribute to poor mental health. However, schizophrenia can be a heritable disease. Genetic factors might also play a part. A process called social drift may be taking place. This is when people suffering from mental illness move into low-income, poorer neighborhoods. In a recent study, published this month in Translational Psychiatry, a group led by researchers at the University of Oxford assessed genetic and environmental influences in three different cohorts of Swedish individuals: 2,386,008 siblings, 1,355 twin pairs and molecular genetic data collected from blood samples in another group of twins. The genetic influences that influence schizophrenia risk and living in poverty later in life were also a factor in their analyses.

Genetics is a better explanation for mental illness than urban living, according to the authors. Amir Sariaslan (a postdoctoral researcher at Oxford in psychiatry) says that the key question we are trying to solve is "selection, who ends-up living in deprived areas and why." It is impossible to assume that environmental effects are causal without doing some testing.

He believes prior studies may have overstated the importance of city-related environmental influence on schizophrenia. "I have not seen a single study that has adequately addressed familial confounding in the association between urban living and similar sort of exposures and later adverse outcomes," Sariaslan says. Many epidemiological studies assess familial risk by accounting for family history, but another study conducted by Sariaslan and his colleagues (published 2015 in Schizophrenia Bulletin) found that this had a much smaller effect than cousin and sibling comparisons. While most experts agree that urban living is associated with an increased risk of psychosis, some do not share Sariaslan’s conclusions. "This study does not compare, in my view, with the very, very strong evidence that does suggest an environmental effect of being born in a city," Meyer-Lindenberg says. One of his concerns with the current study is that it focused on residence in adulthood, when it is very likely that the effects of the urban environment happen around birth or early childhood. In fact, another recent study that found evidence for social drift concluded that this effect still could not explain the mental health risk in urban areas and pointed to the importance of considering whether a study addressed risk before or after disease onset.

To understand the impact of city living on mental health, scientists will need to consider both environmental and hereditary factors. "Emphasizing the role of genes over the environment-or vice versa-is an overly-reductionist approach to the science, and ignores the fact that both sets of factors are relevant to psychosis onset," says James Kirkbride, a psychiatric epidemiologist at University College London who was not involved in the new studies. "No one is denying genetic factors, overall, contribute a greater extent to risk, but of the two, only environmental influences can be ameliorated currently." According to Kirkbride, the science confirms that efforts to reduce the negative impact of urban living should focus on disadvantaged neighborhoods, where the cycle of poor mental health may persist across generations.