For years, scientists have seen an association between city living and psychiatric disturbances such as schizophrenia in adults. Now they have investigated twins to see how much urban life is already affecting children. Especially two factors became apparent.
Almost all over the world, humans are moving into cities. Attracted by workspace, cultural opportunities, mobility, and medical care, nearly two out of three people will be living in cities worldwide by 2050. City planners and sociologists are not the only ones interested in the consequences of this shift. Studies have shown that city people have a nearly doubled risk for developing schizophrenia as compared to people living countryside. This can already be observed in children. But what is the reason? To identify the origins of this risk, psychologists have investigated the living situation of several hundred twins. Their summary: Psychiatric disturbances surface especially where a neighborly solidarity is missing and violence and crime were experienced.
More than 2000 children were included in a study by Candice Odgers and colleagues of Duke University as well as Helen Fisher from King’s College London. They all were derived from a scientifically well-characterized twin cohort in Great Britain, born between 1994 and 1995. To learn more about their social environment, scientists explored where the children were living. They asked their mothers, evaluated data from Google Street View, and sent thousands of questionnaires to neighbors within the same ZIP code area. They focused on four questions: How strong is support and solidarity in the neighborhood? Has there been trouble in the environment such as graffiti, vandalism, roisterous neighbors and heavy fights? How likely is intervention in case of problems? And do violence and crime happen in the surrounding?
Subsequently, the scientists attempted to identify through direct contact with the children who had already shown psychotic symptoms. When twins were 1 years old, they were asked to tell whether other people had read their thoughts at one occasion, or whether they had once heard voices that nobody else could hear. The result: 7.4% of children living in cities had developed at least one psychotic symptom such as hallucinations or delusions, while in children in a rural environment, this statistic was 4.4%. The biggest risk factor were crimes and a missing solidarity among neighbors; they could explain nearly one-fourth of the observed association, as the researcher explains in the journal Schizophrenia Bulletin (1).
Overwhelmingly, not all children that exhibit a psychotic symptom will develop a psychosis later on. However, such early experiences increase the disease risk. Furthermore, it is established that these children will more likely suffer from depression, post-traumatic stress disorder, and drug dependency later in life. This study will help us identifying characteristics of neighborhoods that may be dangerous for children’s health, explains Odgers. Since psychotic symptoms in children are rare, however, scientists are advised to explore other studies as well as other potential etiological factors, such as noise and air pollution.
Furthermore, it is important to identify the biological mechanisms that lay the groundwork for the observations. “Does continuous social stress in the neighborhood decrease the ability of the children to cope with such stressful experiences?” is one of the questions first author Joanna Newbury asks in a press release of her university. Respective hints are available.
Scientists at Heidelberg University, Germany, among them Andreas Meyer-Lindenberg, Director of the Central Institute of Mental Health in Mannheim, have shown in a study that people living and born in a city show a stronger activation of the amygdala and cingulate cortex that people living in a rural environment. Both brain areas participate in emotional processing. A stronger activation is not, per se, a problem. It is known, however, that such activation may also be associated with depression and anxiety disorders. In 2011, Meyer- Linderberg, senior author of the study, pointed out that the results provide a first hint towards a social stress system in the brain that may be the basis for the strong influence of an urban environment on psychiatric disturbances (2).
- Newbury J, Arseneault L, Caspi A, Moffitt TE, Odgers CL, Fisher HL. Why are Children in Urban Neighborhoods at Increased Risk for Psychotic Symptoms? Findings From a UK Longitudinal Cohort Study. Schizophr Bull. 2016 Nov;42(6):1372-1383.
- Lederbogen F, Kirsch P, Haddad L, Streit F, Tost H, Schuch P, Wüst S, Pruessner JC, Rietschel M, Deuschle M, Meyer-Lindenberg A. City living and urban upbringing affect neural social stress processing in humans. Nature. 2011;474:498-501.
This is part 2 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon.