Residential green space in childhood can protect against schizophrenia

Diet and lifestyle 13. apr 2021 3 min Assistant Professor Kristine Engemann Jensen Written by Kristian Sjøgren

Danish research shows that children who grow up with access to green space have a lower risk of developing schizophrenia than children without such access, mostly in urban environments. Green space needs to be integrated into urban planning, says the researcher.

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A new Danish study shows that growing up near green space is good.

Researchers investigated how residential green space in childhood is associated with the risk of developing schizophrenia.

Children who grew up in rural areas have a significantly lower risk of developing schizophrenia than children growing up in urban areas, and this risk is in addition to any genetic risk.

According to a researcher behind the new study, these results should provide food for thought for future urban planning.

“We know that green space benefits mental health, cognition and possibly now also the risk of developing schizophrenia. We should therefore consider incorporating more green space into urban planning, since this may influence the development of some mental disorders and can eliminate some stress factors,” explains Kristine Engemann Jensen, Assistant Professor, Section for Ecoinformatics and Biodiversity, Department of Bioscience, Aarhus University.

The research has been published in Schizophrenia Bulletin.

Green space benefits mental health

Researchers have long known about how people in urban and rural areas differ in well-being.

For example, urban areas have a higher proportion of residents with schizophrenia than rural areas.

This pattern applies to many countries, and the percentage of people with schizophrenia in some cities is more than twice as high as in the countryside.

Studies in Denmark and elsewhere have shown that one probable reason is that more people with schizophrenia migrate to cities, possibly because they can blend in more easily or have better access to help. However, these studies have also shown that migration cannot explain the entire difference between urban and rural environments.

“In addition to migration, something in urban environments must increase the risk of developing schizophrenia. One obvious factor is a prominent difference between city and country: access to green space. Nature and green space are well known to benefit people in providing calm, reducing stress and promoting well-being,” says Kristine Engemann Jensen.

Children from urban areas have increased risk of developing schizophrenia later in life

Kristine Engemann Jensen used Denmark’s Civil Registration System to determine where people lived as children and other registries to determine whether they have been diagnosed with a mental disorder.

She then linked these data to satellite images of Denmark to determine the access children in Denmark had to residential green space and whether they developed schizophrenia later in life.

“Children who grew up near green space, whether in cities or in the countryside, showed a lower relative risk of developing schizophrenia than children who grew up with the least access to green space,” explains Kristine Engemann Jensen.

Kristine Engemann Jensen also adjusted her data for known confounders that might influence the risk of developing schizophrenia, including the parents’ socioeconomic status and family history of mental illness.

“After adjusting for these confounders, we still end up with an increased relative risk of 50%. This means that children who grow up in an urban environment without good access to residential green space may have up to 50% higher relative risk of developing schizophrenia than children with good access to green space,” says Kristine Engemann Jensen.

She emphasizes that the results are based on registry data and therefore show statistical associations rather than causal relationships.

Access to green space more important than genetics

However, the big question is whether the results just reflect genetic differences between the people studied.

The researchers investigated this by studying data on genetic risk among 19,746 people from the Integrative Psychiatric Research (iPSYCH) cohort in Denmark.

Their genomes were mapped, and the presence of genetic mutations linked to an increased risk of developing schizophrenia was identified.

“We examined how much of the risk of developing schizophrenia stems from genetics and how much may be linked to access to residential green space in childhood,” explains Kristine Engemann Jensen.

Although researchers do not yet have a full overview of how much genetics affects the risk of developing schizophrenia, the new results indicate that access to residential green space in childhood appears to have a slightly greater effect than genetics.

Access to green space was associated with 50% lower relative risk, whereas genetic liability was associated with a higher relative risk of 1.24. Green space in childhood explained 1.45% of the statistical variation in risk, and genetics explained 1.01%.

“This is a very exciting field because science does not yet understand what happens at the molecular level when access to green space affects mental health. Perhaps nature has a relaxing effect on the brain, which in turn can be affected by stress in cities, which are much noisier. We also know that air pollution seems to increase the risk of developing schizophrenia,” says Kristine Engemann Jensen.

Healthier urban environments have economic benefits

Kristine Engemann Jensen says that you should not panic if you live in an urban area and your children are growing up in a city.

The association between childhood residential green space and the risk of developing schizophrenia was linked to opportunities to experience nature, which people can still have in cities.

But according to Kristine Engemann Jensen, there may be other perspectives related to urban planning to ensure that people have access to green space, which appears to protect their mental health.

“Integrating green space into urban planning can have many benefits. More and more people have mental disorders worldwide, and we may be able to counteract part of this increase, both for serious mental disorders such as schizophrenia but also for the epidemics of stress, anxiety and depression. This costs society an incredible amount of money and ensuring a mentally healthier urban environment may be a good investment for society,” concludes Kristine Engemann Jensen.

Association between childhood green space, genetic liability, and the incidence of schizophrenia” has been published in Schizophrenia Bulletin. In 2017, the Novo Nordisk Foundation awarded a Challenge Programme grant to co-author Clive Sabel for the project Big Data Centre for Environment and Health.

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