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Gwynne Mhuireach

Student in Landscape Architecture, University of Oregon

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Does urban “green” harbor healthier microbes?

We evolved in natural environments, characterized mainly by soil, water, vegetation, and the innumerable microorganisms associated with each. Many researchers have observed linkages between human well-being and exposure to green space, including mental restoration, reductions in disease and mortality, better birth outcomes, and decreased crime and violence. Explanations for why these benefits are observed are often based on the idea that humans are evolutionarily predisposed to prefer environmental settings that confer survival advantages, namely landscapes that are similar to the savannas and woodlands that humans are thought to have inhabited for thousands of years. Is it possible that vegetation is a source of the microbes we have co-evolved with over the millennium and whose presence we may require for physical and psychological health?

Westernized societies are plagued with increasing rates of auto-immune disorders. A recent study in New York City has shown that kids in neighborhoods with more street trees are less likely to have asthma, after controlling for socioeconomic factors. Several other research studies have found that children exposed to higher environmental diversity (i.e. living on a farm or forested rural setting versus living in a city) were exposed to higher microbial diversity and had lower rates of asthma and allergic disposition.

If we could quantify the relationships among human health, microbial diversity and urban green space, would it change the way we design cities? Should we put a higher priority on providing adequate green space for all urban residents? Majora Carter says, “Race and class are extremely reliable indicators as to where one might find the good stuff, like parks and trees, and where one might find the bad stuff, like power plants and waste facilities.” How can planners and designers ensure that all city residents will have a positive and equitable microbial experience as they interact with the invisible urban microbiome?


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    May 22 2013: I would be interested in seeing any data from New York City comparing rates and appearances of auto-immune disorders of people living in the heart of the city compared with those who live close to Central Park.
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      May 22 2013: There was a paper published by Hanski et al. (which we all read for class) http://www.pnas.org/content/109/21/8334.long that correlated auto-immune disorders of kids in houses to the diversity of vegetation surrounding their homes and the diversity of bacteria on their skin (higher plant diversity correlated with higher skin microbiome diversity and lower allergy risk).

      What do you think could be done in this type of study that would go beyond correlation? How could we get at mechanism?
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        May 22 2013: Another paper similar to the Hanski et al. article: http://www.nejm.org/doi/full/10.1056/nejmoa1007302
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        May 22 2013: I think to get at a mechanism we would have to investigate what microbes are associated with asthma and other allergies and auto-immune disorders and if inoculation (or de-inoculation) of any particular strain or set of strains could be found to induce asthma/allergies or another type of auto-immune disorder in mice, or another model system.
        Such a study (or more likely set of studies) would predicate upon researchers actually knowing what causes asthma, and I don't know if that's known yet or not.
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          May 22 2013: I agree - and I believe this would entail research on the human microbiome.
        • May 24 2013: Discover magazine actually mentions the (what I believe to be the aforementioned article in PNAS). It really gets at this idea of being around microbes and plants may contribute to preventing allergies under that the hypersensitivity results from underexposure to microbes, a thought that I and others on this conversation have mentioned: http://blogs.discovermagazine.com/80beats/?p=36985#.UZ_lpJxaT7o.

          It is interesting to think that part of what keeps our microbial biome in check actually is the diversity and that the lack of microbial diversity can have a negative impact on our health. Moreover as of late there has been a large push for less use of anti-bacterial soap and antibiotics out of concern of resistant bacteria strands arising.

          Another question to consider that is a little off topic is what household products are we using in part to clean as well as reduce our exposure to harmful microbes that may negatively impact the microbial diversity in a household/office environment and in turn people's health.

          Here is a recent article about a prevalent anti-bacterial chemical, triclosan and the ongoing safety review by the FDA of its use in household products such as antibacterial soap : http://globalnews.ca/news/529843/fda-wrapping-up-safety-review-of-chemical-in-antibacterial-soap-after-40-years-of-delays/.

          It is curious to think that our attempt to remove "bad" microbes using cleaning products actually may itself have health risks.
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        May 22 2013: I just think that yes, more research needs to be done (at least for allergies) instead of just correlating low allergy occurrences with living proximity to green spaces. I grew up in the country and have had ridiculous grass allergies my whole life. I also have a friend that grew up in the country that has very bad allergies. There are a lot of factors that could come into play: regional specificity, type of microbes, etc.

        Making cities more green is absolutely a great idea in my eyes, but on the allergy side, increasing greenery could increase people's disposition to acquiring an allergy, especially if current research suggests that the urban population has a higher incidence of it.

        I know there is a whole lot more involved in this idea but there is my input on the allergy side
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      May 22 2013: The "CIties and Biological Diversity Outlook" cites this study as evidence for the impact of street trees on asthma prevalence in NYC children: http://jech.bmj.com/content/62/7/647.short
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      May 22 2013: Or, maybe look at stress hormone levels of folks who regularly go to parks and other such green spaces compared to folks who don't. An article in NYT Well section reported that people who live near parks have lower levels of cortisol, a stress hormone, and children with an attention deficit disorder can concentrate better on cognitive tests after walking through a park. A study reported on in the article found that subjects who spent ~25min walking through a park had lower levels of 'brain fatigue' compared to subjects who spent ~25min walking through an urban area. Since the article just reported on differences in stress levels of adults who lived near parks, it would be interesting to see if regularly using parks can be as effective for stress hormones as just living 'near' a park (whatever near means here).
      However, most of the information out there seems to point to the huge benefits of access to parks and other green spaces, even if we don't know all the reasons for their benefits, so it seems like we should be planning cities with access to parks in mind.


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