Background: Evidence on the effects of residential green spaces on asthma is contradictory. We investigated potential association between the amount of greenness in the residential area during pregnancy and early life and development of asthma in the first 27 years of life. Methods: The study population included all 2568 members of the Espoo Cohort Study, Finland. We calculated individual-level exposure to green space measured as cumulative Normalized Difference Vegetation Index (cumNDVI in unit-months) within 300 m of the participant’s residence during pregnancy and the first two years of life in both spring and summer seasons. The onset of asthma was assessed using information from the baseline and follow-up surveys. Results: Exposure to residential greenness in the spring season during pregnancy was associated with an increased risk of asthma up to 6 years of age, with an adjusted hazard ratio (aHR) of 3.72 (95% confidence interval (CI) 1.11-12.47) per a unit increase in cumNDVI. Increased greenness in the summer during pregnancy associated with asthma with an aHR of 1.41 (95% CI 0.85-2.32) up to 6 years. The effect was found to be related to increased greenness particularly during the third trimester of pregnancy, with an aHR of 2.37 (95% CI 1.36-4.14) per unit increase of cumNDVI. These associations were weaker at the ages of 12 and 27 years. No association was found between NDVI in the first two years of life and the development of asthma. Discussion: Our findings provide evidence that exposure to greenness during pregnancy increases the risk of developing asthma.

Changes in land use and climate change have been reported to reduce biodiversity of the environment and human microbiota. This may lead to inadequate and unbalanced stimulation of immunoregulatory circuits and ultimately, to clinical diseases, such as asthma and allergies. We summarised available empirical evidence on the role of inner and outer layers of biodiversity in the development of asthma, asthma-like symptoms, and allergic sensitization. We conducted a systematic search in SciVerse Scopus, PubMed MEDLINE, and Web of Science up to 5 December 2022 to identify relevant studies assessing the relations between inner and outer layers of biodiversity and the risk of asthma, wheezing and/or allergic sensitization. We applied random-effects models to calculate summary effect estimates. The protocol was registered in PROSPERO (CRD42022381725). Of 75 studies, 20 provided effect estimates for the meta-analysis showing an association between high outer layer biodiversity and a low risk of asthma development (Shannon diversity index: OR (95% CI) = 0.77 (0.55; 1.06); bacterial richness: OR (95% CI) = 0.74 (0.57; 0.96)). Although the evidence on the effect of inner layer biodiversity suggested that bacterial diversity was slightly higher among individuals with asthma, there was no clear evidence of a significant association between inner layer biodiversity and the risk of asthma, wheezing or allergic sensitization. The weight of evidence suggests that environmental exposure to high biodiversity may protect from the development of asthma, whereas there was no consistent evidence on any association between inner layer biodiversity and asthma, wheezing or allergic sensitization.

Background: Previous inconsistent evidence on effects of green space on the development of allergic rhinitis could be explained by the season of exposure. We explored whether the season and timing of exposure to green space play a role in the development of allergic rhinitis during the first 27 years of life. Methods: In a longitudinal study of 2568 participants from the Espoo Cohort Study, green space was assessed using the mean Normalized Difference Vegetation Index (NDVI) within 300 m of the participant’s residence during pregnancy and the first two years after birth during spring and summer seasons. We applied Cox proportional hazards regression to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (95% CI) for the associations between cumulative exposure to NDVI (1-unit increase) and allergic rhinitis. Results: Early-life exposure to abundant vegetation during the spring was associated with an increased risk of allergic rhinitis at 12 years of age [aHR (95% CI) = 1.726 (1.078; 2.765)] and 27 years of age [1.703 (1.139; 2.545)]. However, abundant vegetation during the summer was associated with a decreased risk of allergic rhinitis at 12 years of age [0.754 (0.585; 0.972)] and 27 years of age [0.801 (0.649; 0.989)]. Perinatal exposure to green spaces had no effect on allergic rhinitis. Conclusions: Green space has opposite effects on the development of allergic rhinitis in the spring and summer: early-life exposure to green spaces during the spring increases the risk of developing allergic rhinitis, whereas exposure to greenness in the summer decreases this risk.

This is a Letter and does not include an abstract.