Obesity is a known risk factor for type II diabetes, heart disease and some forms of cancer. Evidence is now mounting that obesity is also a risk factor for asthma. Reports have shown that nearly 75 percent of emergency room visits for asthma have been among obese individuals; other studies have shown that obesity pre-dates asthma. The risk for developing asthma increases with increasing obesity among individuals. Yet little is known about how obesity influences asthma.

In the May issue of the Journal of Allergy and Clinical Immunology, researchers from the physiology program at the Harvard School of Public Health describe factors that may contribute to this link between obesity and asthma. In obese people the lungs are under-expanded and the size of breaths is smaller. These factors make it more likely that their airways will narrow. In addition, there is chronic low-grade systemic inflammation in the obese. This systemic inflammation appears to originate in fat tissue. Inflammation can affect the smooth muscle in the airways causing the airways to narrow excessively.

There are also changes in the blood levels of hormones derived from fat tissue in the obese that may affect the airways. One of these hormones, leptin, is pro-inflammatory and obese individuals have higher leptin levels than lean individuals. Leptin is found at higher levels among asthmatics regardless of the extent of obesity. In contrast, blood levels of another hormone, adiponectin, which has anti-inflammatory properties, are actually lower among obese individuals.

"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," says Jeffrey Fredberg, PhD, co-author of the study and professor of bioengineering and physiology at the Harvard School of Public Health.

Research on the link between obesity and asthma in the authors' labs is supported through grants from the National Institutes of Health and the National Institute of Environmental Health Sciences.

Source: Harvard School of Public Health