Effect of greenness on asthma in children: A systematic review.
Kim Hartley, Patrick Ryan, Cole Brokamp and 1 others
PMID 31899558WHAT IT FOUND
Greenness showed no consistent direct link to child asthma.
Some studies suggested benefit only when greenness was considered alongside traffic, smoke, or family factors. The exposure was measured so differently that stronger conclusions are not possible.
Key findings
01Six of the seven reviewed papers found no statistically significant direct association between greenness and child asthma, while one found a 6% lower risk for a 1 standard deviation increase in a satellite greenness measure (NDVI).
02Three papers reported greenness as protective through interaction with other factors, such as difficult family relationships, traffic, or smoke.
03A prior 2017 meta-analysis of three studies found no overall association (pooled odds ratio 1.01, 95% CI 0.93-1.09).
STILL TO COME
How it was doneWhat they foundWhat it means for RNs
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What it does not show
All included studies were observational, so they cannot prove that greenness causes changes in asthma. Greenness was defined and measured differently across studies, including different terms, vegetation indices, and distances from the home. Associations often lost statistical significance after adjustment for socioeconomic and household factors. The populations, ages, asthma outcomes, and exposure timing varied across studies. The review excluded studies already covered in a previous review, so it updates rather than replaces the whole evidence base.
Declared interests
Funded by the Robert Wood Johnson Foundation, University of Cincinnati, and Cincinnati Children's Hospital Medical Center. The supplied text does not report author conflicts of interest.
The easy way to misread this
Do not read this as evidence that planting trees or adding green space will reduce childhood asthma. The review is observational, mostly null for direct effects, and inconsistent greenness measurement prevents firm conclusions.