September 4, 2008 (Portland, Ore.) – Obese people who have asthma are nearly five times more likely to be hospitalized for the condition than non-obese people with asthma, according to a Kaiser Permanente study published in the September issue of the Journal of Allergy and Clinical Immunology.

This is the first study to control for the risk factors – smoking, use of oral or inhaled corticosteroid medications, gastroesophageal reflux disorder, and demographics – that might explain the obesity-asthma association. Previous studies have shown that obese people are more likely to suffer asthma than non-obese people, and that obese patients often have more severe asthma than their non-obese counterparts.

More than 20 million Americans have been diagnosed with asthma. Nearly a third of adults with asthma are also obese, according to researchers. The Centers for Disease Control and Prevention defines obesity as having a Body Mass Index of 30 or higher (http://www.cdc.gov/nccdphp/dnpa/obesity/defining.htm)

Researchers at Kaiser Permanente Center for Health Research in Portland, Ore., and the Kaiser Permanente Institute for Health Research in Denver surveyed 1,113 patients in Oregon, Washington, and Colorado, age 35 and older, who have persistent asthma. The researchers asked the patients about their weight, height, smoking habits, other illnesses, treatment and their asthma-specific quality of life, asthma control and asthma-related hospitalizations.

“The big finding here is that even after adjusting for risk factors, obese adults were nearly five times more likely to be hospitalized for their asthma,” said study lead author David M. Mosen, Ph.D., MPH, of the Kaiser Permanente Center for Health Research. “Given that nearly 30 percent of our country is obese, this study is yet another example of the long-term dangers of obesity, along with heart disease, diabetes, stroke and dementia.”

The study uncovered these findings:

• Obese people with asthma had significantly worse asthma control, lower asthma-related quality of life, and had 4.6 times higher risk for asthma-related hospitalizations than non-obese asthmatics
• Obese people with asthma were younger and less educated than non-obese people with asthma
• Obese people with asthma used more oral corticosteroids
• Obese people with asthma had a higher incidence of gastroesophageal reflux disorder.

“The take-home message of this study for clinicians is that obese people with asthma need to be followed more carefully because it’s harder to control their asthma, so they are more likely to end up in the hospital,” said study co-author Dr. Michael Schatz, Chief of Allergy at Kaiser Permanente San Diego Medical Center. “My advice for obese asthmatics is: be vigilant to keep your asthma symptoms in check, make sure you know what to do when your symptoms worsen, and do whatever you can to lose weight.”

Source: Kaiser Permanente

“We were disappointed not to find a ‘smoking gun’ that would explain the common association between obesity and asthma,” said lead researcher, D. Robin Taylor, M.D., of the University of Otago in New Zealand. “However, this research points us to other possibilities that future research should examine.”

The results were reported in the first issue for September of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

“We hypothesized that the low-grade systemic inflammation present in obesity would augment the inflammation of asthma (a synergistic effect),” wrote Dr. Taylor. “Or alternatively, that the inflammation of obesity might affect the airways independently (an additive effect), perhaps resulting in mixed airway inflammation.”

In order to determine if there was indeed an interaction between systemic and local inflammation, the researchers recruited 79 women—20 who were obese with asthma, 19 who were of a normal weight with asthma, 20 who were obese but who did not have asthma and 20 controls.

Asthmatics were told to stop using their anti-inflammatory inhaler treatment to avoid confounding effects until “loss of control.” After the withdrawal period of four weeks, subjects underwent blood tests and tests for biomarkers of systemic and airway inflammation, such as C-reactive protein (CRP) and cytokines in blood and inflammatory cells and cytokines in sputum. Those that are known to be relevant in both obesity and asthma were chosen. The researchers then analyzed for interactions between systemic and airway-specific markers of inflammation.

“What we found was that although inflammatory cells and other biomarkers of inflammation were increased, there was no significant interaction demonstrated between obesity and asthma,” said Dr. Taylor.

Although their inflammation hypothesis was not supported by their results, Dr. Taylor points out that it does provide valuable direction for future research. “This does not change the fact that there is a well-established link between asthma and obesity. Sometimes a negative result is important, and the results add to our body of knowledge regarding the obesity-asthma link. Now we need to look in other directions for the answers.”

Animal studies suggest that changes in innate immunity may occur with obesity. “We did not look at this in our patients. Given that asthma is immunologically driven, this is a potential avenue for further research,” said Dr. Taylor. “Alternatively, it may be that dynamic changes in lung function that occur with episodes of asthma are different with excess body weight.”

Whatever the link is, uncovering it will have important clinical implications. “Obese patients with asthma are more difficult to treat because their response to bronchoconstriction is exaggerated and gives the impression that the asthma is worse,” said Dr. Taylor. “They may well have worse symptoms, but not as a result of underlying airway inflammation. Still, the typical response is often to increase their inhaled anti-inflammatory therapy. This is unlikely to provide the answer and may even do harm. The answer lies in dealing with the obesity itself.”

Source: American Thoracic Society