Between 250,000 and 300,000 adults suffer from asthma in Denmark. (Photo: Shutterstock)

Asthma might weaken the body’s immune system

Individuals with asthma suffer more infections and should be under greater medical supervision, says scientist behind new study.

Individuals with asthma do not only suffer from problems with their airways and lungs. They also suffer from a greater number of infections elsewhere in the body, shows new research.

The risk of infections is almost as high as that observed in diabetics.

“We’ve known for many years that individuals with asthma have a higher risk of lung infections than others. But it’s entirely new that this is also true for infections outside of the lungs,” says lead-author Jens Helby Petersen, a doctor at Herlev and Gentofte Hospital, Denmark.

The results are published in the Journal of Internal Medicine.

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Hay fever and eczema do not increase the risk

The study is based on 23 years’ worth of data on 105,519 people obtained from two large Danish population registers: the Copenhagen City Heart Study, and the Copenhagen General Population Study.

Helby and colleagues divided the participants into four groups according to whether they suffered from asthma, hay fever, eczema, or none of these.

They focussed on young, non-smokers to ensure that the participants did in fact have asthma and were not misdiagnosed with chronic obstructive pulmonary disease (COPD), which can cause similar symptoms.

They then calculated the infection rate of each group and the risk of an individual within that group of contracting an infection.

The results showed that individuals diagnosed with asthma before age 50 have a 40 per cent higher risk of infection outside the lungs. No such increased risk of infection was observed in the hay fever and eczema groups.

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Does asthma weaken the immune system?

The results suggest a connection between asthma and the immune system’s ability to fight off infections, says co-author Professor Stig E. Bojesen from Herlev and Gentofte Hospital and the Institute of Clinical medicine at the University of Copenhagen.

“The immune system in individuals with asthma seems to ‘forget’ earlier contact with harmful microorganisms more quickly and is therefore worse at fighting infections,” says Bojesen.

But there are other possible explanations, he says.

“The larger number of infections could be due to the body’s weaker immune system as it fights asthma. This immune modulation is a reasonable response, but it could also make it easier to contract infections. Other research will need to establish this. The tendency to contract infections is probably established early in life, coinciding with the typical début of asthma” says Bojesen.

Professor Thomas Vorup-Jensen, a professor at the Institute of Biomedicine, Aarhus University, Denmark, also struggles to explain the results, but suggests that harmful microorganisms can enter the body via the lungs.

“When asthma causes lung damage, they may allow more bacteria and viruses into the body, causing infection,” says Vorup-Jensen, who studies the immune system. He was not involved in the new research.

Read more in the Danish version of this story on

Translated by: Catherine Jex

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