In fastly urbanizing societies people experience a slow divorce from natural environments. Built environment ‒ asphalt and concrete ‒ literally cuts our roots. Biodiversity hypothesis of health alerts us to think: where are we going and can we change the course?
A Finnish research group has investigated allergy in the Finnish and Russian Karelia for 20 years. The setting is intriguing as after the Second World War, Soviet Union left Russian Karelia undeveloped and as a barrier against Western influence. The people maintained small scale agricultural life-style and subsistence economy. This was also the case on the Finnish side in 1940s and 1950s, which started to change with urbanization and technological development.
Photo 1. The research site in Russian Karelia, Pitkäranta, is located on the Northern shore of lake Ladoga. Photo: Peter LeSouef 2003.
In school children, the prevalence of allergy was manifold in Finns compared with Russians. Among children living in Pitkäranta, located at the Northern shore of Lake Ladoga, the pollen and food allergy were almost non-existent. The Russians also had much less asthma than the Finns. In adults, an important observation was made. In those born in 1940s, there was no allergy difference between the Finns and Russians, but in those born in 1980s the difference was already manifold. The Finnish adults had much more allergies than the Russians adults. What would explain such a contrasting process after the war?
The basic genetics did not explain the allergy contrast. The genetic differences between the Finns and Russians were small and not connected to the mechanisms of inflammatory pathways. What about common environmental chemicals? They were measured in serum samples but again: no explanation. Then the microbes, bacteria and fungi, were targeted and analysed in drinking water and house dust. Heureka! There were much more living microbes and microbial elements in the Russian water and dust. It was obvious that the microbial exposure on the Russian side was stronger than on the Finnish side, due to different lifestyle and environment. Microbes determine much of the gene expression, e.g. by activation and de-activation of various inflammatory pathways. That would give a plausible explanation of the striking allergy (immunological) differences between the two populations.
With Ilkka Hanski, we made a hypothesis and asked, whether environmental biodiversity affects the observed allergy differences? We characterized the environments the children live in, examined their microbiota, and analysed the immune balance. Finally, all these determinants were put in the same statistical model. Indeed, diversity of the natural environment (macrodiversity) associated with the microbiota richness of the children's skin (microdiversity), and that, in turn, with balanced immune response. Contact with diverse natural enviroment seemed to protected from allergy. Results from two other Finnish studies supported these observations.
Photo 2. A Finnish research group has investigated allergy in the Finnish and Russian Karelia for 20 years. This photo was taken on April 30 2014 by Helena Minkkinen. From left to right: Kaisa Koskinen, Johanna Vendelin, Laura Paalanen, Pia Karisola, Leena von Hertzen, Lasse Ruokolainen, Tiina Laatikainen, Harri Alenius, Vladimir Masyuk, Tari Haahtela (principal investigator), Mika Mäkelä, Ilkka Hanski, Pekka Jousilahti and Lars Paulin. Missing from the photo: Petri Auvinen, Nanna Fyhrquist, Timo U. Kosunen, Mirja Salkinoja-Salonen and Erkki Vartiainen. In Northern Karelia the study has been undertaken by Vesa Korpelainen and Tiina Vlasoff and in Russian Karelia Olga Markelova, Mihail Uhanov and Elmira Zilber.
Individual's immune defence needs constant training for an appropriate response against environmental micro-organisms, and that is provided by a rich natural environment. Birch pollen on nasal mucosa or peanut in the mouth are not dangerous and worth of inflammatory defence. In contrast, pathogenic bacteria or viruses need fast response to stop them to spread in the body.
The microbial training starts from the birth, maybe even in utero. The exposure is concrete: what we eat, drink, breathe and touch. Microbes of our evolutionary home, from soil and natural waters, invade us and are constantly modified by environment and lifestyle (especially nutrition). The genetic entity of the microbiota is titled the microbiome, which is also called the ”second genome” of human. Many protective functions of the body are outsourced to the microbiome, which has intimate cross-talk with the environment.
The Karelia Allergy Study gave birth to the biodiversity hypothesis, first for allergy and then for immune balance and health in general. Paradoxically, the notorious Iron Curtain may be thanked for that! Tari Haahtela
Professor Emeritus, HUS, Skin and Allergy Hospital, University of Helsinki