Obesity and Asthma
Obesity and Asthma Are LinkedThe rates of both asthma and obesity are rising in North America, and they are rising together. The Centers for Disease Control (CDC) reports that about 30% of adults in the US are obese, a rate that has almost doubled in the past 20 years. The percentage of adults in the US who have asthma has also risen, with current rates at about 8% of the population. READ MORE
That’s not just a coincidence: there is a strong link between obesity and asthma. All over the world, studies have found that obese individuals are more likely to develop asthma. In fact, being even moderately overweight increases your risk of having asthma. Overweight and obese individuals have a 38% and 92% higher risk, respectively, for developing asthma than people of normal weight.
It seems clear that obesity can, in some way, cause asthma. But the relationship between obesity and asthma is complex. How, exactly, the two disorders are related remains a mystery. The cause-and-effect relationship is not totally clear cut, because not everyone who is obese has asthma. LESS
Effects of Obesity on AsthmaObese people aren’t just more likely to have asthma, they’re also more likely to have severe and persistent asthma. The more obese the individual, the more severe and persistent the asthma is likely to be. Obese people with asthma are also more likely to be hospitalized than nonobese people with asthma. READ MORE
Asthma is harder to control in someone who is obese as well. Obese individuals with asthma are more likely to take asthma medications than nonobese people with asthma. But they are less responsive to standard asthma medications, such as inhaled corticosteroids. The more obese someone is, the less responsive that person is likely to be to asthma medication. LESS
Does Losing Weight Help?When obese patients lose massive amounts of weight, the results are consistent: their symptoms improve and they are able to use less medication. However, some symptoms, such as airway hyperresponsiveness, may not disappear.
Possible Reasons for the LinkScientists don’t know just how obesity is linked with asthma. Many theories have been put forward:
- Inflammation. To many researchers, the link between obesity and asthma seemed clear. Because fatty tissue is metabolically active and secretes a number of inflammatory chemicals, being obese creates a chronic, low level of inflammation throughout the body. So asthma and obesity share a common pathology: chronic inflammation.
To see if the increased level of inflammation in obesity is related to asthma, a number of studies have looked at the presence of eosinophils in the airways of obese individuals with asthma. (The presence of eosinophils in the airways is a hallmark of asthma.) Not only was no correlation found, but in some cases there was an inverse correlation—meaning that the more obese an individual was, the fewer eosinophils were present.
Other studies have looked at the effect of cytokines (inflammatory agents released by fatty tissue) on the lungs, and have found some correlations. But a recent study discounted the role of systemic inflammation in creating the typical type of airway inflammation associated with asthma. It is possible that other, still unknown forms of inflammation are involved. So the jury is still out on the relationship between inflammation, obesity, and asthma.
- Allergies. Having allergies is a well-known risk factor for asthma, so it’s been theorized that obesity may be a risk factor for allergic responses. But a recent epidemiological study found that the risk of asthma in obesity isn’t related to whether or not the individual has allergies.
- Insulin resistance. Individuals who are obese frequently have decreased sensitivity to insulin. However, the same epidemiological study that found no relationship between asthma and allergies also found that there doesn’t appear to be any relationship between insulin resistance and asthma.
- Comorbidities: Gastroesophageal reflux disease (GERD) and sleep apnea. Obesity is associated with GERD. It’s been theorized that GERD could lead to asthmatic symptoms in people with asthma, possibly through vagal nerve stimulation caused by acid refluxing into the esophagus and/or inhaling tiny droplets of acid into the bronchi. Some obese people who have been treated for GERD have had improvement in their asthma symptoms.
Obesity is also associated with sleep apnea, a breathing disorder characterized by brief interruptions of breathing during sleep. There is some evidence that sleep apnea may have a role in the development of asthma: in obese persons with identical BMIs, severe asthmatics had a higher rate of sleep apnea than moderate asthmatics.
More Possible Reasons for the Link
- Genetics. Mutations have been found in certain chromosomal regions in individuals who have asthma and who are obese. These regions contain genes for receptors relevant to both asthma and obesity. One gene, for instance, controls both airway tone and metabolic rate. Other mutations have been found in regions associated with inflammatory mediators.
- Mechanical factors. Mechanical—that is, having mostly to do with physical dynamics—factors undoubtedly have something to do with the increased risk of asthma in the obese. Because the chest wall bears large amounts of excess weight, it is more difficult for the chest of an obese person to rise and fall. Having excess fat in the abdomen also raises the diaphragm and limits its motion. This makes it more difficult for the individual to inhale and exhale deeply and leads to a lower overall lung capacity, causing wheezing and shortness of breath and possibly contributing to asthma.
- Hormones. Fatty tissue produces many different hormones that have a strong effect on the body’s functioning and may contribute to asthma. One hormone in particular, leptin, seems implicated in asthmatic inflammation. Leptin is found at high levels in people with asthma. It has an overall pro-inflammatory effect. It activates pro-inflammatory cells, promotes T-helper 1 responses, and mediates the production of the other pro-inflammatory cytokines, such as tumor necrosis factor-a, interleukin (IL)-2, and IL-6.
Leptin also stimulates the growth of blood vessels and recruits monocytes and macrophages (types of white blood cells). An increase in leptin levels may cause an imbalance between the production of Th1 and Th2 cytokines. This imbalance is implicated in the development of asthma.
- Misdiagnosis. Up to a third of obese people who have been diagnosed with asthma do not actually have it. As explained above, having a great deal of weight pressing on the chest can lead to wheezing and shortness of breath, symptoms that may be misdiagnosed as asthma.