Asthma is a very common condition. In developed countries between three and six percent of the total population have asthma. Asthma occurs more frequently in children with approximately one in five children suffering from the condition. In children, it is more common in boys than girls. In adults, men and women are equally affected.
Is Asthma More Common In Some Countries Than In Others?
Asthma occurs in every country in the world although there are marked differences. Most developed countries have a similar level of asthma – approximately six percent, with Australia at 13% and New Zealand with the highest incidence at 20%.
Asthma is far less common in the developing world. It was so rare in Papua New Guinea that there is no native word for asthma. There has however been a steep rise in the incidence recently.
In India and Africa, only about 3% of the population have asthma, and most of these people live in cities.
There is currently no certain answer to explain the differences in rates of asthma.
So Are We Genetically More Likely to Develop Asthma or Is It The Way That We Live?
Some years ago an interesting natural experiment occurred. A severe hurricane hit the island of Tokelau in the South Pacific and the entire population was forced to move to New Zealand. On the Tokelau Islands asthma was virtually unknown. After the move, asthma became widespread, particularly amongst children. This suggests that it is not so much genetic differences but the environment that causes asthma.
Asthma surveys in developing countries show that asthma is more prevalent in cities than in rural areas. In Kenya, asthma is virtually unknown in the villages, yet it is increasingly seen in the cities. Why urbanisation should make a difference in developing countries is not yet known. In developed countries there is no difference between rural and urban asthma levels. Theories put forward include: diets become more westernised, the standard of living is higher, exercise rates decrease, more dustmites and more pollution.
However, others argue against these factors. For example, Tokyo has a much higher incidence of pollution than Wellington, New Zealand, yet the asthma incidence is at least five times higher in Wellington than in Tokyo. Another study exploring why the Isle of Skye has the highest incidence of asthma anywhere in the UK, revealed that there was no pollution nor dust mites, on Skye.
The cause of asthma is still being hotly debated. Perhaps genetics give us a predisposition to asthma. Environment and lifestyle may effect these genetic types, causing a higher incidence of asthma in those who are genetically disposed to become sufferers.