I have often been asked if growing up in a big city, with its pollution, noise, social isolation, and high-risk diseases contributes to excessive stress, anxiety, and depression. On the one hand, it would seem self-evident. Yet, on the other, there’s evidence suggesting that mental illnesses are largely determined by our genes. Then there’s the cop-out, "mental illnesses are only genetically pre-disposed, but activated by environmental influences."
I noted an interesting article from Scientific American about the connection between schizophrenia and urban living (which was first noted in Sweden and Denmark in the 1930’s). Current studies find that growing up in the city doubles the risk of psychosis later in life as well as heightens the risk of other mental health issues such as depression and anxiety. Add to this that over 50% of the world’s population resides in cities, and with an estimated 66% by 2050, we had better get our act together.
Although the majority of studies have focused on adults, what may matter most is being born or growing up in a city. Researchers at King’s College London and at Duke University, conducted a longitudinal study with 2,232 twin children in the United Kingdom to measure possible psychotic symptoms at ages 5 and 12.
They found that growing up in the city nearly doubled the likelihood of psychotic symptoms at age 12, and that exposure to crime and social isolation among neighbors, were the biggest risk factors. Although children with these psychotic symptoms would not necessarily develop schizophrenia as adults, it was suggested that these symptoms could serve as markers for other mental health issues including depression, post-traumatic stress disorder and substance abuse.
According to experimental evidence at the University of Heidelberg, being in the city does something to a specific circuit in the brain that impairs our ability to deal with social stress. It was found that living in or growing up in cities showed stronger activation in the amygdala and cingulate cortex (brain areas involved in processing and regulating emotion), respectively, compared with those from rural areas. More recently, they discovered that the stresses of migration, another well-established risk factor for schizophrenia, led to similar alterations in brain function.
Yet, it can be argued that people with schizophrenia and mental illnesses are more likely to move into poor, deprived city neighborhoods. In a recent study at the University of Oxford, genetic and environmental influences were assessed 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. They found genetics as a stronger explanation than urban living for explaining the occurrence of mental illness.
The take-away is that both genetic factors and city life have an impact on mental health. Since there’s not much we can do about heritable factors, we should focus our efforts to reduce the negative impact of city life in disadvantaged neighborhoods, where the cycle of poor mental health can persist across generations.
This blog was co-published with PsychResilience.com