Global warming 'could increase asthma misery'

Global warming could lead to more people suffering the misery of asthma, new research suggests today.

A major study of almost 670,000 children has found a clear link between indoor humidity and asthma rates in western Europe.

Every 10% increase in indoor humidity was associated with a 2.7% increase in the prevalence of asthma symptoms, the researchers found.

House dust mites, which trigger asthma attacks, thrive in moist air, and humidity encourages mould which can irritate the airways.

The study also found that places where average outdoor humidity dropped below 50% for at least one month a year had lower rates of asthma.

Warmer temperatures caused by climate change are expected to drive up humidity levels, especially in cities.

Experts believe summers in the city will get stickier because of the “urban heat island” effect caused by asphalt and concrete trapping heat at night.

The impact of climate change was acknowledged by the authors of the asthma study, led by Dr Stephen Weiland, from the University of Ulm in Germany.

Writing in the journal Occupational and Environmental Medicine, they said the evidence showed that climate can affect rates of asthma and eczema in children.

The researchers added: “This may also have implications for the assessment of potential health effects due to climate change.”

The scientists found that temperature, altitude, humidity and latitude all influenced the prevalence of asthma and eczema.

Information was collected between 1992 and 1996 from children aged six to seven, and 12 to 13, from more than 50 countries.

The research formed part of a major worldwide investigation called the International Study of Asthma and Allergies in Childhood (ISAAC).

When the data were analysed, they showed the strong link between indoor humidity and asthma rates for both age groups.

The trend emerged in western Europe, where the study focused on 57 centres in 12 countries.

Increasing latitude was associated with higher rates of eczema, and higher outdoor temperatures with lower rates.

An association has been seen before between thunderstorms and higher numbers of hospital admissions due to asthma. But little is known about the effect of long-term climatic conditions on the disease.