Tom Spears
The Ottawa Citizen
June 8, 2004

For years, obese Canadian women have been taking drugs to treat their asthma -- a condition that new research in Ottawa suggests they may not have after all.

In some cases, says Dr. Shawn Aaron, the problem appears to be their weight, and nothing else. Excess weight presses all the muscles in the respiratory system and causes breathing difficulties that look a lot like asthma.

"The weight is a load on the chest wall," said Dr. Aaron. "Every time you breathe in, you expand your chest wall. And these people have the equivalent of a 20-pound block on the chest, preventing their lungs from expanding."

The key is that when they lose weight, the breathing problems disappear. You can't lose asthma this way. Maybe, then, it wasn't really asthma to begin with.

The research by Dr. Aaron's group from the Ottawa Health Research Institute, Ottawa Hospital and University of Ottawa appears in a journal on lung and heart diseases called Chest. For unknown reasons, obese women are diagnosed with asthma far more often than thin women. (The same isn't true in men.)

The researchers enrolled 58 women in a six-month weight reduction program, with a strict diet, exercise and counselling. The women weighed an average of 254 pounds at the beginning, and 41 per cent suffered from asthma.

The women lost an average of 44 pounds, or 17.4 per cent of their original weight. For every 10 per cent of their original weight the women lost, they improved their lung capacity by five per cent. The improvement was most noticeable in women with the greatest weight loss. But as their lung capacity improved, there was no change in the "reactivity" of their airways.

That's the defining feature of asthma: the upper airways are squeezed partly shut, often in a reaction to allergens such as dust or pet hair.

This suggests the problem may not be asthma, but rather the sheer strain of breathing with overburdened muscles, the researchers concluded.

Dr. Aaron, a respirologist, says the study suggests some obese women "may be misdiagnosed" as having asthma, but it is not final proof. If they are being misdiagnosed, "it might mean that you're on a lot of medicines that you may not really need, such as inhaled steroids or bronchodilators," and that these may not work very well anyway, he said. He hopes a longer study will test these findings.

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