In a modern, urban environment like Singapore, parents balk at the thought of their kids rolling in dirt or touching anything that creeps on the ground. However, our latest research suggests that exposure to natural environmental microbiota during a woman's preconception, pregnancy and postnatal periods can have a positive impact on her little one's predisposition to allergies.
The Nurturing Effect of Nature
19 Nov 2021
By Evelyn Loo and Lau Hui Xing
As the COVID-19 pandemic rages on, frequent sanitising and staying indoors has become part of a typical Singapore household. Isolation from germs appears to have become synonymous with staying healthy.
While this is true for pathogens, eradicating all microbes including beneficial ones may increase the risk of developing non-communicable diseases such as allergies.
Good to "get dirty"
The hygiene hypothesis proposes that exposure to a diverse microbial environment or “being dirty”, especially from a young age, can boost the immune system and protect against allergies1. This theory is supported by a number of studies around the world.
The URECA birth cohort from the U.S. reported that children exposed to increased bacterial diversity in household dust during the first year of life had a reduced risk of atopy and atopic wheeze2.
The PARSIFAL and GARBRIELA birth cohorts from Europe showed that children living in farms had lower rates of asthma and other allergic diseases compared to children from suburban areas due to an increased exposure to the environmental microbiome present in farming homes3. Another study conducted in a childhood centre in Portugal showed that frequent outdoor play alleviated asthma and eczema symptoms in children4.
During pregnancy, maternal exposure to farm animals was found to protect the offspring against allergy development5. This is because beneficial environmental microbes can affect maternal immune responses by regulating the bacteria communities that reside on and in the maternal skin and gut. This in turn influences immune responses in the foetus and reduces allergic inflammation.
Strong evidence on the involvement of microbial diversity is presented by a human intervention trial in Finland which showed that enriching the microbial diversity of daycare centres by covering the yard area with sod and forest floor caused an increase in microbial communities that reside on the skin and in the guts of children, as well as stimulated their immune responses6.
The dilemma of city-living
With urbanisation, children have significantly reduced contact with nature which may upset their microbiome balance. Furthermore, staying home all the time increases exposure to house dust mites that may lead to allergic sensitisation7.
By studying the Singapore Preconception Study of Long-Term Maternal and Child Outcomes (S-PRESTO) cohort, we were able to find further evidence of the importance of environmental microbes in protecting against eczema8. We collected dust by vacuuming the living room floor and the parents’ bed and/or infant’s cot to determine their microbial communities – the child was then assessed for eczema by clinicians.
Interestingly, we found that children with eczema had higher levels of pro-inflammatory human-associated bacteria (Actinomyces, Anaerococcus, Finegoldia, Micrococcus, Prevotella and Propionibacterium) and lower levels of the environmental microbe Planomicrobium at all timepoints. Planomicrobium originates from environmental sources such as soil and lakes, and has also been detected in mattress dust from farming environments9,10. Planomicrobium inhibited human-associated bacteria were particularly found in households of children without eczema. In support of our findings, a study by the PASTURE birth cohort identified seven protective outdoor-associated microbiota present in indoor dust, commonly found in sources such as soil, water and compost, which were linked to a lower risk of asthma11.
Another study conducted in Finland showed that walking inside non-farm houses with shoes worn outdoors increased the similarity of house microbial composition to that found in farm houses and resulted in lower risks of asthma development at age six years12.
Seek the great outdoors
Taken together, our study shows that natural environmental microbial exposure can modulate the microbes we shed in an indoor environment and further affirms the protective effect of nature against allergy. It is likely that we need a diverse range of human-associated and natural environmental bacteria to train our immune system during early life to minimise development of allergic diseases.
The famous mountaineer John Muir once said: “In every walk with nature one receives far more than he seeks.” Indeed, spending more time in the great outdoors has other wide-ranging benefits that go beyond reducing the risk of allergies. Research shows that interacting with nature can also improve mental health and cognitive function, as well as reduce metabolic disease risk in the general population13, 14, 15.
Whether you are a child, expectant mother, or even a couple planning for a baby, spending more time outdoors has far-reaching benefits for your health and well-being. So get out there today and reap the benefits that nature has to offer!
- Haspeslagh E, Heyndrickx I, Hammad H, Lambrecht BN. The hygiene hypothesis: immunological mechanisms of airway tolerance. Current Opinion in Immunology. 2018;54:102-108.
- Lynch SV, Wood RA, Boushey H, et al. Effects of early-life exposure to allergens and bacteria on recurrent wheeze and atopy in urban children. J Allergy Clin Immunol. 2014;134(3):593-601.e512.
- Ege MJ, Mayer M, Normand A-C, et al. Exposure to Environmental Microorganisms and Childhood Asthma. New England Journal of Medicine. 2011;364(8):701-709.
- Bento G, Dias G. The importance of outdoor play for young children's healthy development. Porto Biomedical Journal. 2017;2(5).
- Douwes J, Travier N, Huang K, et al. Lifelong farm exposure may strongly reduce the risk of asthma in adults. Allergy. 2007;62(10):1158-1165.
- Roslund MI, Puhakka R, Grönroos M, et al. Biodiversity intervention enhances immune regulation and health-associated commensal microbiota among daycare children. Sci Adv. 2020;6(42):eaba2578.
- Green WF, Marks GB, Tovey ER, Toelle BG, Woolcock AJ. House dust mites and mite allergens in public places. The Journal of allergy and clinical immunology. 1992;89(6):1196-1197.
- Ta LDH, Tay CJX, Lay C, et al. Household environmental microbiota influences early-life eczema development. Environmental Microbiology. 2021;n/a(n/a).
- Shivaji S, Srinivas TNR, Reddy GSN. The Family Planococcaceae. In: Rosenberg E, DeLong EF, Lory S, Stackebrandt E, Thompson F, eds. The Prokaryotes: Firmicutes and Tenericutes. Berlin, Heidelberg: Springer Berlin Heidelberg; 2014:303-351.
- Birzele LT, Depner M, Ege MJ, et al. Environmental and mucosal microbiota and their role in childhood asthma. Allergy. 2017;72(1):109-119.
- Karvonen AM, Kirjavainen PV, Taubel M, et al. Indoor bacterial microbiota and development of asthma by 10.5 years of age. J Allergy Clin Immunol. 2019;144(5):1402-1410.
- Kirjavainen PV, Karvonen AM, Adams RI, et al. Farm-like indoor microbiota in non-farm homes protects children from asthma development. Nat Med. 2019;25(7):1089-1095.
- Kondo MC, Jacoby SF, South EC. Does spending time outdoors reduce stress? A review of real-time stress response to outdoor environments. Health & Place. 2018;51:136-150.
- Oh B, Lee KJ, Zaslawski C, et al. Health and well-being benefits of spending time in forests: systematic review. Environmental Health and Preventive Medicine. 2017;22(1):71.
- Berman MG, Jonides J, Kaplan S. The Cognitive Benefits of Interacting With Nature. Psychological Science. 2008;19(12):1207-1212.
ABOUT DR EVELYN LOO
Dr Evelyn Loo is a principal investigator at the Singapore Institute for Clinical Sciences (SICS) and an adjunct assistant professor at NUS Yong Loo Lin School of Medicine's Department of Paediatrics. Her research interests include the study of epidemiology of a child's health, as well as identifying critical periods where environmental microbiome can exert the most influence and factors that can affect environmental microbiome. Armed with a better understanding of the interactions between environmental microbiome and allergens, Dr Loo hopes that her research will be useful in the implementation of strategies to prevent childhood diseases such as eczema.
ABOUT LAU HUI XING
Lau Hui Xing is a research officer on Dr Evelyn Loo's team. She assists with manuscript writing, literature review and data analysis of studies on paediatrics and allergy. She also has a special interest in environmental issues and hopes to work on the elimination of microplastics in the future.