Green and privileged childhoods signal better adult mental health

Two studies link parks and poshness to lower depression and cognitive decline, for reasons still unclear. Paul Biegler reports.

A childhood full of parks and privilege correlates with lower risk of mental illness in later life.

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As cities boom and high-rise living becomes the norm, planners might want to listen up to a new study that finds a childhood without green space increases the risk of mental illness.

The study, led by Kristine Engemann from the Department of Bioscience at Aarhus University in Denmark, used satellite imagery to measure vegetation around the childhood homes of nearly a million Danes born between 1985 and 2003.

The Landsat pictures were used to draw a 210 by 210 metre box around each person’s house at age 10, then calculate a greenery index. The study included people across the urban-rural divide, but only those whose long-term mental health outcomes were on record.

And here’s why you shouldn’t take your local park for granted.

As greenery round the childhood residence shrunk, risk of mental illness as an adolescent and adult went up. Kids who grew up in plots with the least vegetation had a 15 to 50% greater incidence of a range of psychiatric problems, including depression, eating disorders, anxiety and obsessive compulsive disorder.

The association held even when researchers adjusted results for potential confounds such as a family history of mental illness or social disadvantage.

The study is yet more evidence of a disturbing trend: cities seem to be bad for your mental health. Existing studies, the researchers write, show city folk have a 50% higher risk of psych disorders and urban kids are at double the risk of schizophrenia.

The burning question is why.

No one is sure, but the authors have suspects. A fast-pace lifestyle could make city dwellers more stressed, a well-known risk factor for mental illness. Four out of five cases of depression, for example, come after severe stress. The calming effect of parks and gardens and the space to exercise and socialise could act as stress busters.

The researchers also point to data showing a link between air pollution and mental illness, possibly from effects on brain development. “The role of green spaces as natural filters of environmental pollution,” they write, may be protective.

A third possibility is that close contact with nature can encourage a healthier microbiome – the billions of bacteria that live in and on you – and better immunity, both of which may lower risk for mental illness. Gut bacteria, for example, can make gamma-aminobutyric acid (GABA), a chemical messenger active in the brain. Low levels of GABA have been linked to depression.

Panning back, the study is pertinent to the burgeoning shift in design based on American biologist E O Wilson’s biophilia theory, the idea that humans evolved to feel happier in environments most likely to support life. That is, not concrete jungles. So-called biophilic design uses neuroscience to guide construction of buildings and landscapes that make us feel good.

“These findings contribute to our understanding of the urban environment as an important environmental risk factor for mental health and can guide the design of healthy city environments, as well as institutions and programs affecting childhood life, for example, school systems,” the authors conclude.

The reach of “the long arm of childhood,” however, is not limited to mental health. Whether you luck out as a kid also influences cognitive function in older age, according to a new study led by Marja Aartsen from Oslo Metropolitan University in Norway.

It’s no secret that intellectual powers can wane with age. In particular, memory and something called verbal fluency – the ability to recall words in certain categories – take a hit.

There are a few things that can be done to stave off the decline, however, including exercise, getting a partner and keeping up your social network. But the researchers found something you can’t control has a big say in how well people age cognitively: childhood privilege.

They examined data on more than 24,000 adults aged 50 to 96 taken from the Survey of Health, Aging, and Retirement in Europe (SHARE). SHARE ran between 2004 and 2015 and included a cognitive test every two years. It also asked people how well off they were as kids.

Each person’s level of disadvantage at age 10 was calculated from the main breadwinner’s occupation, the presence of overcrowding and low quality housing, and whether there were fewer than 10 books in the house.

The team found those with the most advantaged upbringing remembered an average of 1.3 more words on a memory task and generated 5.4 more words on a test of verbal fluency.

Childhood privilege, the authors explain, often means more mental stimulation and encouragement of curiosity. Both enhance the brain’s ability to forge new pathways through neuroplasticity. The result, they write, is a “cognitive reserve” that helps those kids in older age.

But in what might be the brain’s version of “the bigger they are the harder they fall” the researchers also found posh kids had the steepest decline in mental function with age.

They’re not exactly sure why, but hazard an explanation: “[T]here comes a time when the neuronal loss can no longer be compensated by cognitive reserve, and we observed an accelerated decline, as if advantaged respondents were catching up,” they write.

These studies add to the growing literature on the social determinants of health; those conditions in which people are born, work and grow old that have deep sway in the kinds of illnesses that mar and often end lives.

Both studies appear in the journal Proceedings of the National Academy of Sciences. They are available here and here.

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Paul Biegler is a Eureka-Prize winning journalist, bioethicist and former physician writing on all things health and science.
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