For the very first time, researchers from Aarhus University have shown that marginal environmental factors can trigger the development of pollen allergy, among other things. Whether you grow up in a large city or a small town is one of them.

2015.08.18 | Kirsten Olesen

Even minor environmental differences during childhood can affect your health.

Is it healthier to grow up in a small town than in an urban area of more than 250,000 inhabitants? According to a new study conducted at Aarhus University, this seems to be the case. At least when it comes to the development of allergies and hypersensitivity to pollen, grass and house dust mites, among other things.

It is a well-known fact that allergies and hypersensitivity are most common in the industrialised countries, and especially among people growing up in the cities: Thus, several studies indicate that the prevalence of allergies is lower among people with a rural childhood.

For the first time, however, the new research project shows that the difference lies elsewhere than previously anticipated. It is not only a question of rural-urban differences; differences in size within urban environments are also a decisive factor.

Size is not all that matters

"Our data clearly suggest that it is not only a matter of extremes, such as the difference between growing up in New York or in New Guinea. Even minor environmental differences during childhood can affect your health – and determine whether you develop allergies. There is a significant decline indicating that the margins are much smaller than previously believed," says postdoc Grethe Elholm from the Department of Public Health at Aarhus University.

"So whether you grow up in Aarhus or Hadsten can actually affect your health as an adult".

She adds that the size of the town or city is not the only criterion: Another important factor is how we choose to live our lives, including the food we eat, the products we use (shampoo, deodorants, cream), whether we take any medication or have any pets, etc. – although theory also suggests that exposing your body to, e.g., bacteria challenges the immune system in a positive way.

The study was recently published in the scientific journal Clinical & Experimental Allergy. It also demonstrates a difference between growing up in a rural area and on a farm with livestock, although the differences are not as significant compared to urban environments.

See abstract of the article 'The Danish urban-rural gradient of allergic sensitization and disease in adults' .

About the study

• The study included 1,236 Danish male participants aged 30-40 from the so-called 'Glostrup cohort' and the Sund Stald cohort (project on young farmers).
• The four categories the researchers focused on were: city (more than 250,000 inhabitants), small town (more than 3,000 inhabitants), rural area (less than 3,000 inhabitants) and farm with livestock.
• The research project was conducted in collaboration with researchers from the Research Centre for Prevention and Health in the Capital Region of Denmark, Glostrup University
  Hospital, the University of Copenhagen, Aalborg University and the company ALK-Abelló.
• A previous study conducted by the same research group at Aarhus University in 2013 showed that the agricultural environment can prevent or reduce hypersensitivity and allergies – even in adults.

Further information

Postdoc, PhD Grethe Elholm
Aarhus University, Department of Public Health – Section for Environment, Occupation and Health
Mobile: +45 2211 2044
gelh@ph.au.dk

Associate Professor, PhD Vivi Schlünssen
Aarhus University, Department of Public Health – Section for Environment, Occupation and Health
Mobile: +45 2899 2499
vs@pu.au.dk

Professor Torben Sigsgaard
Aarhus University, Department of Public Health – Section for Environment, Occupation and Health
Mobile: +45 2899 2426
ts@ph.au.dk