by Emily Oken, MD, MPH

Asthma and obesity are the two most common chronic health conditions affecting both children and adults. The most recent data from the US Centers for Disease Control and Prevention show that about 1 in every 6 US children are obese (17%), and almost 1 of every 7  (14%) will develop asthma by age 18. Both obesity and asthma are on the rise. Could these two conditions be connected? 
The answer appears to be yes. Individuals who are obese are 1½ to 3 times more likely to have asthma. But is the obesity causing the asthma, or vice versa? There are a number of reasons to think that asthma might result in weight gain. For example, because of their breathing troubles, people with asthma may be less likely to exercise regularly, thus putting them at some risk for weight gain. Also, some medicines used to treat asthma, including steroid inhalers or oral corticosteroids, can cause weight gain if taken frequently or for a long period of time.

However, most evidence suggests that it’s probably mostly the other way around – obesity causes asthma. In one analysis that summarized data from over 333,000 adults who did not currently have asthma, those who were obese had almost twice the odds of developing asthma in the future compared with those who were normal weight. 

Excess body fat probably affects breathing in a number of ways. Extra weight around the chest and abdomen can make it harder for lungs to expand. That extra weight can also cause acid reflux, which can in some cases result in stomach acid splashing all the way up the esophagus into the lungs. The stomach acid can be a chemical irritant to the airways, causing restriction of them, just what happens in asthma.

Most importantly, though, excess body fat causes inflammation, which has effects throughout the body including on the airways. Further, people who are obese tend to eat more fats and carbohydrates, which further increase inflammation, and less fruits and vegetables, which are rich in the anti-oxidants that help reduce inflammation and oxidative stress. 

But, that’s not all. Possible “upstream” exposures in very early life might increase risks for both asthma and obesity at the same time. We have previously found that during pregnancy a maternal diet rich in anti-inflammatory omega-3 fatty acids is associated with lower child BMI; higher levels of these same fats in umbilical cord blood were associated with better immune function.   Also, maternal cigarette smoking during pregnancy – which causes a great deal of inflammation – is a strong predictor of both obesity and asthma in the child. Professor Diane Gold and I are currently collaborating on a project to examine early life oxidative stressors and antioxidants in relation to allergy and lung function in the early teen years. Stay tuned for some interesting results in the future. 

Unfortunately, obese individuals with asthma tend to have more severe symptoms and also respond less well to medication. In one study from the Kaiser Permanente health system, obese adults with asthma were 4.6 times more likely to have an asthma-related hospitalization compared with those with asthma who were not obese. The good news is that a healthful diet rich in anti-oxidants will probably help both weight control and asthma. The more we understand about these connections may help us to understand how to treat both at the same time. 



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