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Obesity-Linked Lung Stress May Trigger Asthma

Harvard team spots links between overweight, respiratory trouble

THURSDAY, May 12, 2005 (HealthDay News) -- Lung compression may be a key factor linking asthma and obesity, new research shows.

There's increasing evidence that excess weight gain raises risks for asthma, but little is known about physiologic links between the two.

This new study, conducted by experts at the Harvard School of Public Health, Boston, found that the lungs of obese people are underexpanded and the size of their breaths smaller, making it more likely that their airways will narrow.

"Obesity has the capacity to impact lung function in a variety of ways. None of them are good and all of them are poorly understood. More research is needed to explain the relationship between asthma and obesity," study co-author Jeffrey Fredberg, professor of bioengineering and physiology, said in a prepared statement.

Obese people also have chronic low-grade systemic inflammation, which may originate in fat tissue, the investigators report. This inflammation can affect the smooth muscle in the airways and cause them to narrow excessively, the study said.

A third factor contributing to asthma risk lies in the fact that obese individuals also experience changes in blood levels of hormones derived from fat tissue -- hormones that may affect airways. One of these hormones, leptin, is pro-inflammatory, the researchers note. Obese people have increased leptin levels compared with lean people, and leptin is also found in higher levels in people with asthma, regardless of their weight.

Also, blood levels of another hormone, adiponectin, which has anti-inflammatory properties, are lower in obese people than in lean individuals, the researchers report. They published their findings in the May issue of the Journal of Allergy and Clinical Immunology.

More information

The U.S. National Heart, Lung, and Blood Institute has more about asthma.

SOURCE: Harvard School of Public Health, press release, May 10, 2005
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