When you are rooted, you don’t have to wait for such research studies. In culture of sacred grove, immune disorders like asthma were non-existent.
Ancient Indian scriptures, while advocating conservation of sacred forests, do highlight the importance of planting trees and groves. For example, the Vriksotsavavidhi of the Matsyapurana attaches great importance to the planting of trees and even to the celebration of the tree festival or ‘vana mahostav’. It emphasizes the importance of planting a tree thus: “A son is equal to ten deep reservoirs of water and a tree planted is equal to ten sons”. A tree laden with flowers and fruits saves its dependents (birds, humans, etc.) from distress, just as a good son saves his family.
When the British first came to India in the 17th century, this element of Indian society left them completely confused. For them, first as traders and then as colonial rulers, forests were meant to be exploited for economic gain; animals (where they existed) needed to be hunted either for foodor sport. In 1878, in a small village called Vedanthangal, near Chennai, British soldiers shot some storks in the local wetland. The villagers stormed the collector’s office and made him issue an order that no one would harm the nesting birds in future. This is by no means the only example of its kind; Indian history is peppered with such examples. Among the best known are the Bishnoi, in Rajasthan, Punjab and Haryana who are famous for their self-sacrificing defence of wildlife. 
In such culture, Asthma is impossible. Not only asthma, any immunity disorders are impossible.
Here is an mundane research reestablishing fact that smart city without ample trees, is curse for the population.
Humanities Environmental Conservative Management Systems Sushmita Jha Goswami
Land cover and air pollution are associated with asthma hospitalisations: A cross-sectional study
Natural environments in urban areas were associated with less asthma hospitalisation.
These associations varied by coexisting background air pollution concentration.
Green space/gardens were associated with less asthma when NO2/PM2.5 was lower.
Urban trees were associated with less asthma when NO2/PM2.5 was higher.
Green space and gardens were associated with reductions in asthma hospitalisation when pollutant exposures were lower but had no significant association when pollutant exposures were higher. In contrast, tree density was associated with reduced asthma hospitalisation when pollutant exposures were higher but had no significant association when pollutant exposures were lower.
We found differential effects of natural environments at high and low background pollutant concentrations. These findings can provide evidence for urban planning decisions which aim to leverage health co-benefits from environmental improvements.