Over half a century, the proportion of Danish people with hay fever and asthma has tripled, and the symptoms of asthma occur earlier in life, according to new research in Clinical and Translational Allergy.
Over fifty years, the proportion of young Danes who experience allergy symptoms because of pollen has grown from 7 to 8% t in the 1970s to 24% today. And the proportion of people who have asthma has risen from 4 to 12% during the same period. This is shown by a study of 53,000 Danish blood donors published by researchers from Aarhus University in collaboration with the Blood Bank at Aarhus University Hospital.
“In the newly published study, 53,000 blood donors from all over the country born in the period from the 1950s and up until the turn of the millennium, completed a questionnaire on a tablet while donating blood,” says the lead author of the study, Susan Mikkelsen, a PhD student at the Department of Clinical Medicine and a medical specialist in clinical immunology. Mikkelsen also works as a physician the at Department of Clinical Immunology at Aarhus University Hospital.
“The blood from 25,000 of the participants has also been examined for antibodies against nine selected allergens, ranging from different types of pollen to animal hair and dust mites. In medical language, we say that the test participants who react by forming antibodies are ‘sensitized’,” she explains.
The blood samples show that the proportion of sensitized donors increases with the number of allergic disorders. For example, the researchers can see that 90% of those who indicate that they have both asthma and allergic reactions in the nose and eyes, form antibodies.
On the other hand, the proportion of sensitized is only half as large for donors who grew up on a farm with animals, where they are exposed to a range of bacteria, fungi and pollen that might be protective against hypersensitivity.
Mikkelsen also points out that the newly published study is a so-called conservative research result which cannot be accused of exaggerating the problem – it most likely downplays it. The blood donors are in fact not representative random sample of the Danish population, as they are healthier, in particular the oldest blood donors, due to the requirement that a donor must be ‘healthy’ to give blood.
“For us, this means that the severe asthmatics aren’t included when we calculate the proportion of allergy sufferers, because they simply aren’t allowed to give blood. When every fifth blood donor nevertheless ticks the box as allergic and every tenth as asthmatic, this of course tells something about how hay fever and asthma are today very common diseases,” says Mikkelsen.