Asthma rate triple world average

By MARTIN JOHNSTON, health reporter

New Zealanders suffer asthma at three times the global rate, according to the first international assessment of the disease.

The New Zealand-led assessment, which combines previous studies, estimates that 300 million people, about 5 per cent of the global population, suffer asthma.

The rate among New Zealanders is 15 per cent.

The prevalence of the disease is rising - particularly where populations are urbanising and adopting Western lifestyles - but the basic reasons remain unclear.

The latest study, for the World Health Organisation and the Global Initiative for Asthma, is published today to coincide with World Asthma Day.

It predicts that by 2025, some 400 million to 450 million people will have asthma, an increase of up to 50 per cent.

The lead researcher, Professor Richard Beasley, director of the Wellington-based Medical Research Institute, said last night that the study provided the first firm estimate of the disease's global prevalence using standardised data.

He said the rising prevalence was driven by a growing population, people shifting from rural areas to cities and the spread of Western habits.

"We know that with the adoption of urban and Western lifestyles the rate of asthma goes up markedly.

"One of the strong factors from studies, particularly in developing countries, is that asthma prevalence rates are much higher in cities than in rural areas.

The exact features of the lifestyle associated with urban living have not been identified with certainty in terms of why their rates are so much higher."

The research report says that when people from Southeast Asia and the Pacific Islands emigrate to Australia and New Zealand there is a marked increase in asthma prevalence within one generation.

Many scientists are investigating the "hygiene hypothesis" - that increasingly sanitised living conditions and a decreasing exposure to bugs early in life primes the immune system to overreact later, producing allergic diseases. Most asthma is triggered by allergies.

Professor Beasley said this theory explained part of the rise in asthma, "but it's not the whole answer".

Despite New Zealand's high asthma prevalence, the rate of people dying from the disease is within the range of many Western countries at 4.6 per 100,000 asthmatics.

At the Western extremes, Canada's rate is 1.6 and Denmark's 9.3. The world's worst rate is in China, at 36.7.

"New Zealand used to have far a higher mortality and case-fatality rate," Professor Beasley said.

They had fallen steeply in the past 10 years because of the withdrawal of the drug fenoterol, which was dangerous when overused, the greater use of inhaled corticosteroids and the use of asthma management plans.

ASTHMA BURDEN

Global prevalence of asthma estimated to be 300 million people or about 5 per cent of the population.

New Zealand prevalence 15 per cent.

225,723 people died from the disease worldwide in 2001.

Asthma is 300 times more common than coronary heart disease.

The global economic costs of asthma exceed those of TB and HIV/Aids combined.