The Unique Link Between Obesity and Asthma Risk
A 2018 study in Lung Cellular and Molecular Physiology suggests that the patterns of asthma in people who carry significant excess weight, may have a unique mechanism. The study suggests that under these circumstances, asthma is guided by how the respiratory muscles are affected by obesity. Asthma is traditionally thought of as an airway disease. Adding muscle dysfunction to its pattern adds a new dimension which may change the traditional treatment approach.
Asthma might not be primarily caused by airway inflammation (as is usually observed), but more likely by hyper-responsiveness of the airways. According to the study findings, in asthmatics who are also diagnosed with obesity, the exposure to irritants results in an increased secretion of calcium to the smooth muscle cells of the airways, and that results in the airway obstruction. This is quite different from the traditional inflammatory process in the airways, which causes thickening of the inner mucosal layer.
The relationship between asthma and obesity has been quantified as more causal rather than coincidence. There does appear to be a clear relationship.
The Severe Asthma Research Program (SARP) is a comprehensive study of adults and children with asthma. It has studied the patterns of severe asthmatics, identified clusters of asthmatics that are obese, and defined the different phenotypes in this unique group.
Some of the difficulties when classifying people with obesity are the diagnostic criteria for obesity. Criteria are different for children and adults. In adults, obesity is defined by a body mass index (BMI) of greater than 25. In children, obesity is defined by a weight percentile based on gender and height of greater than the 90th percentile.
Some different characteristics of asthma in the obese population:
- These individuals do not show the characteristic “positive” result on exhaled nitric oxide, a test for airway inflammation
- They do not show the presence of eosinophils commonly seen in asthmatics.
These are possible additional unique factors:
There are co-morbidities in obesity that predispose an individual to asthma, like gastroesophageal reflux and sleep-related breathing disorders.
Another distinct difference is that in asthmatics with obesity there is no association with eosinophils in the disease process. What is observed is the presence of other substances called adipokines, which play a role as inflammatory mediators. Adipokines are substances that attract cells involved in inflammation and they have adverse effects on the airways. These substances are produced by adipose tissue (fat cells). Some of these substances, whose activity influence the airways, include plasminogen activator, monocyte chemotactic factor, leptin (hormone whose levels are increased in obesity), and adiponectin (levels are decreased in obesity).
There are also mechanical factors. Obese people breathe at low lung volumes because of the restriction posed by the large abdomen. These low volumes come close to what is known as the “closing volume.” This term refers to the minimal volume that’s needed to keep the small airways patent or open. The presence of this phenomenon may lead to premature closure of the airways that will not improve with the administration of inhalers, corticosteroids, or bronchodilators. The management of asthma in this case will require “breathing training” and alterations in performing certain activities combined with compensatory breathing techniques. You essentially learn ways to compensate for the impact of the excess fat on your breathing mechanism.
The presence and identification of asthma in obese individuals is often not clear cut. All these features suggest that individuals with obesity should be treated with special considerations.
The novel approach for management of this particular group that involves more than just the use of medications is called shared decision making (SDM). This includes an agreement on preferences of activities, perception of control, and attainable goals. The purpose is to improve quality of life, gain adherence to appropriate medications, and reduce healthcare and hospital visits.
SDM also adds another paradigm of treatment — weight reduction measures including bariatric surgery if indicated. One of the criteria for consideration for bariatric surgery is the presence of co-morbidities like diabetes, and asthma is a potential factor.
Statistics suggest that people who go through SDM, who were deemed to have severe asthma have shown greater reductions in exacerbations.
Given the special needs of this population, more careful assessment and diagnostic criteria is needed to meet the needs of those who have both obesity and asthma. SDM is a novel new approach that still requires further refinement.
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