Asthma Subgroups: Obesity Associated Asthma
Researchers first observed a relationship between obesity and asthma in 1970, and various studies since that time have confirmed the link. This has lead to a lot of research in this area, spawning a 5 of theories attempting to explain the link. Going along with the modern trend of dividing asthma into different subgroups, it only makes sense that one of them is now called Obese Asthma.
What do statistics show?
Obesity is considered a body mass index (BMI) of greater than 30%.1 Over the past several decades there has been a parallel rise in the rates of both obesity and asthma. For instance, between 1980 and 2000, obesity rates rose 50% while asthma rates rose 75%.2,3 As of 2010, 26.8% of people without asthma were obese, although 38.8% of people with asthma were obese.4
Studies show the risk of asthma increases as BMI increases, and the more BMI increases the worse lung function becomes. So, the more obese a person becomes the greater the risk for developing 9 severe asthma, or asthma that his difficult to control even with high doses of inhaled corticosteroids.5, 6, 9 Ultimately, studies show obesity doubles the risk for developing asthma.9, 10
Studies also show a reduction in the quality of life among obese child asthmatics, compared with non-obese asthmatics and also compared with obese children who did not have asthma.5 Obesity increases the risk of developing adult-onset asthma by 50%, and this risk is the same for both women and men.9
What are some theories?
Obesity complicates childhood-onset asthma (COA)
COA is most likely to be allergic asthma diagnosed early in life, and so it's less likely to be caused by obesity. It's more likely that poorly controlled asthma leads to a sedentary lifestyle, which lends itself to obesity. Obesity then complicates COA, making it harder to control.One explanation for this is that adipose (fat) tissue releases a hormone called leptin. While all asthmatics produce this hormone, obese asthmatics have higher leptin levels, and have worse lung function scores, than non-obese asthmatics. Leptin has been shown to have a regulatory effect on the immune system, and to cause it to release inflammatory markers that lead to worsening airway inflammation, more hyperactive airways, and severe asthma.2, 5, 6, 9, 10All asthmatics have increased levels of eosinophils, or white blood cells that play a significant role in airway inflammation and asthma. Leptin activates and prolongs the life of eosinophils, perhaps making airways increasingly hypersensitive to allergens, thereby making allergic asthma more severe.10
If true, better asthma control should result in lowered obesity rates, especially in children.
Obesity causes adult-onset asthma (AOA)
Researchers believe if obesity causes asthma, it's less likely to be due to allergies and hypersensitive airways. They believe it's more likely to result from prolonged exposure to substances released from adipose tissue, such as leptin and inflammatory mediators such as interleukin 6 (IL6), Tumor Necrosis Factor (TNF), and C-Reactive Protein (CRP).9, 10Adipose tissue in lean people consists of about 10% macrophages, white blood cell that destroy cellular debris like dead tissue, infected cells, pathogens, etc. They are pro inflammatory macrophages, meaning they secrete substances like TNF. Adipose tissue secretes a protein called CD163, which increases the number of macrophages in adipose tissue in the obese by as much as 50%. Macrophages secrete Interleukin 8 (IL8), which recruits neutrophils, white blood cells that enhance the inflammatory response. So, some researchers believe the combination of these effects may cause low-grade systemic inflammation, causing persistent airway inflammation, or severe asthma.9, 10If true, weight loss would cause a reduction in asthma severity. While studies in this area are limited, they do seem to show improved asthma control with weight loss. 2
Poor diet causes asthma
A 2010 study showed lung function worsened after eating foods high in saturated fats. Saturated fat may activate the Troll-like Receptor 4 (TLR4) gene, increasing the production of TLR4. This causes asthmatic immune cells to recognize saturated fat as a pathogen, releasing inflammatory markers and recruiting neutrophils, in response to it. This results in persistent airway inflammation, and severe asthma that responds poorly to asthma rescue medicine, a double whammy of sorts.6, 9
If true, efforts to improve diet may result in better asthma control.
The link may be purely coincidental
I attended an asthma forum recently for the Asthma Initiative of Michigan in which a doctor presented information about asthma and obesity, and his conclusion was that the link was merely coincidental. It's possible further research may confirm his suspicion.8
It may not even be asthma
Some obese individuals may be diagnosed with asthma due to obesity associated shortness of breath or air hunger (dyspnea). They are prescribed asthma medicine that fails to work because there is no asthma.
If true, proper testing should rule out asthma. These individuals may benefit from a proper diagnosis and weight loss treatment.
How is obesity-associated asthma diagnosed?
Impeding a proper diagnosis may be a blunted perception of dyspnea in obese asthmatics. They may assume they are short of breath due to obesity, although it’s actually asthma. Methods of diagnosis have yet to be established, although it would seem that proper BMI measurement, along with pulmonary function testing, would be key to obtaining an accurate diagnosis.
How is obesity-associated asthma treated?
At the present time, most asthma guidelines treat asthma as a single disease, meaning they are all treated the same. Future guidelines may be specific to the unique asthma subgroups, meaning specific treatment options specifically tailored for obese asthmatics.
Such treatment may involve asthma controller and rescue medicine. However, studies seem to show that higher BMIs blunt their effects, possibly requiring higher doses, or other treatments altogether. 8, 9
An option for severely obese individuals is bariatric surgery. Some studies do seem to show increased lung function, decreased asthma severity, along with a reduction in asthma attacks and decreased emergency room visits and hospitalizations, after substantial weight loss following bariatric surgery.8, 9
Obese asthmatics are also at an increased risk for developing GERD Asthma. So, this is something that should be considered, especially when asthma is difficult to control and worse at night. If such a diagnosis is made, GERD treatment would be indicated.
What should we make of all this?
Obesity can make asthma more difficult to control. While asthma medicines may be helpful, obesity treatment may be key to obtaining ideal control, although studies are inconclusive. I personally believe that the link between obesity and asthma is not coincidental, and involves a combination of the above theories. What do you think? Let us know in the comments below.
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