KEY POINTS:
For decades parents have been encouraged to get their asthmatic children into the pool, but new reports suggest the very exercise they have been told might remedy respiratory problems may in fact be causing them.
Last week Olympic gold medallist Grant Hackett announced he had been diagnosed with
exercise-induced asthma, or exercise-induced bronchoconstriction (EIB), following years of chronic chest infections, sinus complaints and even a bout of pneumonia.
He is not alone - one in ten Australians are believed to suffer from asthma, but at the past two Olympic Games between 16 and 20 per cent of the national swimming team have claimed to suffer from it.
Swimming Australia this week confirmed around one third of the team are now asthmatic.
The debate in medical circles is about what came first - do a high percentage of swimmers suffer from asthma because they swim, or did they take up swimming because they suffer from asthma?
While some members of the national swim team have admitted they took up swimming as asthmatic children - Libby Lenton and Jessicah Schipper included - there is mounting evidence to suggest a growing number of professional swimmers are developing the illness as a result of their time in the pool.
The Australian Olympic Committee's asthma expert Karen Holzer says all endurance athletes are exposed to the risk of EIB as a result of their training.
"You've got two types (of asthmatics) - the person who has got background asthma that is triggered by exercise, and that's about 90 per cent of people with asthma ... and then you have this other population which is more the elite athletes, particularly those involved in the endurance sports," Dr Holzer told AAP.
"As a consequence of doing a lot of exercise they injure their airways which leads to the development of exercise-induced bronchoconstriction, a form of asthma."
Dr Holzer says 30 to 50 per cent of asthmatic athletes go undiagnosed because they don't realise what they are suffering from.
"It's a gradual thing and that's why so many are not aware that they've got it, because it slowly creeps on, and then that's the way they always feel when they exercise," she says.
"They present in a number of ways - they may get the classical symptoms like the chest tightness and the cough ... but often it might be just a dry irritating cough, or they're puffing a lot more than other people, it can also present with recurrent infections."
Dr Holzer said over all other endurance sports, swimmers were most at risk of EIB because of their exposure to chlorine.
"On the surface of all pools there's a gaseous layer of chlorine and its metabolised gases, that acts as an irritant to the airways ... it's a bit like an occupational asthma," she said.
"Years ago it used to be thought that more people with asthma swum, and that's why the prevalence was so high with swimmers, but now they've found that the chlorine and the metabolised gases are actually irritating the airways and injuring them."
Professor Philip Thompson, director of the Lung Institute at the University of Western Australia, says while there is some evidence that over-chlorinated pools may trigger the illness, the actual act of swimming is not a cause.
"It's fairly straight forward: swimming doesn't cause asthma. There is no evidence of that," Professor Thompson says.
"(But) I think it's not unreasonable to highlight that there is an emerging question mark over whether indoor pools or chlorination is going to be good for asthma or not.
"People who swim in indoor pools have a higher likelihood of developing asthma than those who don't, and that's very much related to the by-products of chlorine."
Professor Thompson says a high level of fitness may have hidden symptoms from a long-term sufferer.
"If you're very fit you'll often tolerate very low levels of asthma activity and not realise that you've got asthma because your fitness overwhelms your awareness of the symptoms," he says.
While in other cases, he says, endurance athletes may be misdiagnosed with EIB simply because their lungs complain when they are pushed to the extreme.
"Some high altitude marathon runners, at the end of their running they appear to have what sounds like asthma, but when ... they're down at normal altitude doing normal things they never have any symptoms and all their breathing tests are normal," he says.
"It raises questions of whether it is asthma or not because the lung only has a few ways of saying it's not happy - you can be breathless, you can cough, you can wheeze, you can have pain, and after that it doesn't vary that much."
Dr Sandy Anderson from Sydney's Royal Prince Alfred Hospital, who is on the International Olympic Committee (IOC) medical commission's independent panel for asthma, says it is only endurance athletes - not everyday swimmers - who are at risk from the condition.
She also said the increased incidence of asthma on the national team would not hurt Australia's Olympic chances.
"[Hackett] has done fantastically well for an athlete for swimming for the Olympic games, but Dawn Fraser had much worse asthma and won more gold medals," she says.
"I guess we've experienced 50 years of asthmatics winning gold for Australia who are swimmers."
- AAP
