Urban dwellers at greater risk of mental illness: Study

By Dr. Ananya Mandal, MDJun 23 2011

A new study shows that living in a city increases the risk of developing a mental disorder, including depression and schizophrenia, compared to people who live in non-urban areas. The findings of the has implications for around half of the world's population who live in cities.

There have been earlier studies that have showed that city dwellers are 21 percent more likely than non-urban residents to develop an anxiety disorder and they have a 39 percent greater risk of for being diagnosed with a mood disorder. There is even an increased risk of the brain disorder schizophrenia, in which patients suffer from delusions and hallucinations.  Experts say the incidence of schizophrenia among those who are born and raised in cities is about two times that of people who live in non-urban areas.

The scientists argue that exposure to daily stress - such as traffic and toxic pollution -  is responsible for the increased risk of mental illness among city dwellers, according to Jens Pruessner, director of  McGill University's Centre for Studies in Aging in Montreal, Canada. He said, “Stress is of course defined in many different ways but one way to capture it is to say what are the daily hassles that you have to cope with?  And you could imagine that if you live in the city, those might be by a large proportion as compared to someone who lives in a more rural environment.”

For the study Pruessner's Center developed something called the Montreal Imaging Stress Task, or MIST, which was used as the protocol for a study of healthy German volunteers. The participants were asked to do mathematical calculations while researchers took pictures of their brains using sophisticated imaging technology, and compared the brain images of volunteers who came from a city of more than 100,000 residents to those of volunteers who lived in rural areas.

Results showed that urban living was associated with a greater stress response in a brain region called the amygdala, which is involved with emotional regulation and mood.  And second brain region, called the cingulate cortex, which is associated with negative mood and stress, was found to be more activated in people who were brought up in cities, according to Pruessner.

He explained, “So even if you no longer live in the city but if you lived for the fifteen years of your life in the city, then this structure remains to be sensitized to stress.” Both the amygdala and cingulate are known to be affected in people with mood disorders.

Speaking of sex differences he said, “Women typically respond less strongly to stress.  At the same time if men do get affected, then their disease progression for schizophrenia seems to be worse.”

“I was surprised by the magnitude and specificity of the findings,” said study author Dr. Andreas Meyer-Lindenberg. The next step, he said, would be to determine what it is about city life that makes it so stressful. Is it the crowding, the noise, the pollution - or something else? He said he hopes the answers might help urban planners design cities more conducive to mental health. To control stress, Meyer-Lindenberg said, city dwellers might try meditation, which can impact neural circuitry. If that doesn't help, he recommends a weekend getaway, adding, “It doesn't hurt to occasionally get out into the country.”

An article describing the association between urban stress and mental disorders is published in the journal Nature.