Large datasets are revealing how our physical environment may influence health.

Creating greener, healthier environments may benefit both brain and overall health.

Not all environmental risks are modifiable, but some may be changed individually or collectively.

Increasing tree canopy, for example, has been associated with lower mortality over time.

I wrote about why nature may be good for our brains in my last post, and just this week, I came across another interesting study that made me think about the question more broadly: How much does the physical environment affect our health and brain?

Impressively, this study was led by medical student. The research team combined high resolution tree canopy estimates, temperature, and mortality data in Chicago over a 10-year period (2011 to 2021). The novelty of this study was not just examining the relationship between tree canopy and health but how changes in tree canopy from year to year were associated with changes in mortality over time.

The finding was striking. Each year-to year-percent increase in tree canopy was associated with about a 10% reduction in mortality. The associations were seen in deaths related to cardiovascular, mental health, musculoskeletal, and respiratory conditions. A 10% reduction in mortality is a whopping number, if we think about what we hope to achieve, say, in a drug trial.

Correlation Is Not Causation

Of course, one of the first lessons in science is that correlation is not causation.

In their study, Chicago’s South and West side had higher temperatures and greater absolute canopy loss over time (despite higher baseline canopy levels) and was associated with increased mortality. These are areas known for economic disadvantage, so we are faced with classic chicken-or-egg dilemma. Was the decline in canopy a reflection of decline in socioeconomic state of the neighborhood? Or perhaps tree canopy was a proxy for other health-promoting factors, such as places to exercise and cleaner air.

This study cannot fully answer what caused what. But it illustrates something else that I find fascinating: epidemiology is changing.........

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