Up to 30% of current allergic asthma could be attributed to a history of childhood eczema and hay fever, suggests a new study.
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SYDNEY: Kids who suffer from both eczema and hay fever are nine times more likely to develop allergic asthma in their forties, according to a study spanning four decades.
The report, currently in press in the Journal of Allergy and Clinical Immunology, draws from the results of a study involving around 1400 participants known as the Tasmanian Longitudinal Health Study (TAHS). Began in 1968 when the participants were seven years old, and followed up in 2004 when they turned 44, it is the longest-running asthma study in the world.
"We were expecting a connection to be found between eczema, hay fever and asthma," said lead author Pamela Martin, a University of Melbourne PhD student based at the Murdoch Children Research Institute in Melbourne.
"However, we were very surprised at how strong the association [was]. We found strong evidence that childhood eczema and hay fever predict for adult allergic asthma."
Explaining eczema and asthma connection
Previous research into these disorders has led to the proposal of three theories to explain the connection between eczema and asthma.
According to Martin, the first theory hypothesises that the two are expressions of the same genetic predisposition towards allergy - a person is fated to be at high risk of allergies (including hay fever and possibly food allergy) throughout their life. "There is evidence to support this," said Martin, "For example, allergies usually run in families."
The second theory considers that environmental factors may be triggering allergies in certain people - and their family members. "For example, exposure to pollens may influence the development of multiple allergies including asthma and hay fever," she said.
The third theory, said Martin, suggests that an inflammatory factor is produced by eczematous skin that travels to the lungs and contributes to asthma development. "A candidate for this theory is Thymic Stromal Lymphopoietin (TSLP), considered a 'master regulator' of the immune system responses that cause allergies," she said.
"In mouse models of eczema, if you block the activity of TSLP, the mice do not go on to develop asthma (or at least the asthma-like syndrome we can observe in mice)."
Watching the atopic march unfold
While several studies in the past have found evidence for what is known as the 'atopic march' in childhood, which sees the progression in a patient from having eczema in the first few years of their life to developing hay fever and asthma a few years down the track, this new study is the first to reveal how it unfolds over four decades of a patient's life.
The results also led to the first evidence of how childhood allergies affect the different types of asthma that can affect people in adulthood - allergic and non-allergic. While a very strong association between childhood eczema and hay fever, and adulthood allergic asthma was discovered, childhood allergies were not found to be linked with non-allergic form of adult asthma.
"Hence there are likely to be different origins for non-allergic asthma - which has different underlying inflammation when compared to allergic asthma," said Martin.
