It appears that growing up on a farm with livestock is not the only factor that protects us against asthma later in life. A new study from Aarhus University shows that growing up in other small and larger environments on the scale between farm and city also affects the risk.

2016.03.09 | Kirsten Olesen

It appears that whether you grow up in a small town or a village is a not insignificant factor in relation to the risk of developing asthma as an adult.

We already knew that growing up on a farm with livestock protects against asthma when compared to growing up in a city. But it now appears that this perception is a little too black and white.

This is shown by a new study from Aarhus University that has been published in the scientific journal International Journal of Environmental Research and Public Health.

The new findings suggest that a protective effect from a childhood environment gradually increases the further away from the city environment you are.

"The farm magic" is gradually diluted

"If we imagine that there is something magical out on the farms, we can now see that this ‘magic’ has also spread to other environments - and that it is, as it were, diluted the closer we get to the city," says the primary author of the paper, PhD student Signe Timm from the Department of Public Health, Aarhus University.

"We still cannot say why this is so, but our hypothesis is that the quantity and diversity of bacteria and fungi that a person will be exposed to in childhood (the microbial exposure) plays a role. The more bacteria found in the environment, the lower the risk of asthma."

The hypothesis is supported by studies that have shown that there are most (and most kinds of) non-pathogenic bacteria and fungi in a farm environment and fewest in towns and cities.

Also a comment on urbanisation

The researchers have analysed data from more than 11,100 people in five Nordic countries, including Denmark. They have defined six environments in the new study: Farm with livestock, farm without livestock, village, small town, suburb and inner city. The trend is clear: The highest level of protection against developing asthma as an adult comes from growing up on a farm with livestock, while growing up in a city provides the lowest level of protection.

What is new is that the effect gradually increases and is different in all four intermediate steps: So more city means less protection. Among those who grew up at one end of the scale - on a farm with livestock, eight per cent developed asthma as adults. At the other end of the scale - in the inner city, the corresponding figure is 11 per cent.

"The study is therefore also a comment on the urbanisation taking place all over the world, and on the consequences that urbanisation appears to have on the pathological picture, especially autoimmune and allergic diseases," says Associate Professor, PhD Vivi Schlünssen from the Department of Public Health, Aarhus University.

•  Read the article ”The Urban-Rural Gradient in Asthma: A Population-Based Study in Northern Europe”

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Facts:

 

• An estimated 300,000 Danes suffer from asthma.
• The study is based on data from 11,123 people in what is known as the RHINE cohort, which covers people born between 1945 and 1973 in Denmark, Norway, Sweden, Iceland and Estonia.
• RHINE (Respiratory Health in Northern Europe) is a research network formed by researchers from Iceland, Norway, Sweden, Denmark and Estonia, which is involved in the European Community Respiratory Health Survey (ECRHS).
• Aarhus University has financed Signe Timm’s PhD degree programme.
• Research councils from several Nordic countries have supported the RHINE project.

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Further information:

PhD student Signe Timm
Aarhus University, Department of Public Health
Mobile: (+45) 2531 8606
signe.timm@ph.au.dk

Associate Professor, PhD Vivi Schlünssen
Aarhus University, Department of Public Health
Mobile: (+45) 2899 2499
vs@ph.au.dk