Asthma is one of the commonest chronic diseases around the globe where it is reported that around 300 million people are suffering of this disease.[I] Asthma is characterized by an inflammation of airways which is reversible presenting with recurrent attacks of shortness of breath, cough and wheeze. These symptoms are due to airflow obstruction, bronchial hyper-responsiveness and airway inflammation, which results in respiratory symptoms.
Obesity is an epidemic where many obese patients present with respiratory symptoms and disease due to the impact of obesity on lung function which is attributed to mechanic and inflammatory aspects of obesity.[ii]
Hence obesity has a major negative impact on both asthma treatment and control. In terms of hospitalization, patients suffering of obese asthma are almost fivefold more likely to be hospitalized than non-obese patients with asthma for an asthma exacerbation. Furthermore, obese patients with asthma have not responded as well as their non obese counterparts to standard controller therapy with either inhaled corticosteroids or combination inhaled corticosteroid/long-acting β-agonist, and they exhibit increased use of rescue therapy.[iii]
Effects of obesity on lung function:
Obesity could have mechanical or physical effect on the lung function could help us gain a greater understanding of the correlation between obesity and asthma.
A study conducted in 2014 by Rasmussen and Hanox[iv] revealed that the lung volume reduction seen was due to impinging adipose tissue hence, reducing the volume of the chest cavity and resulted in a direct mechanical effect.
A relative decrease in functional residual capacity (FRC) and low tidal volumes was observed in most obese patients. Spirometric values of FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) are inversely proportional to BMI, although no association was seen between BMI and spirometric values in elderly patients over 60 years of age. Inverse correlation between FRC and abdominal obesity was revealed, while there was no association with BMI. Fat distribution seems to be important as abdominal obesity elevates the risk of asthma in females in addition to BMI, this gives an indication that better clinical assessment for the risk of asthma could be done using both measures of BMI and waist circumference than either measure alone. Moreover, adiposity increase is correlated with lower lung function regardless of atopic status.
Results in a more recent study performed in 2018 by Forno et al. have further confirmed the effects of obesity on asthma. It showed that both overweight and obesity linked with higher incidence of asthma, asthma morbidity, and resistance to therapy. It also shows that weight gain precedes the development of asthma symptoms and that obese individuals have reductions in lung function. An inverse correlation between (BMI) and lung volumes indicates that obesity leads to a decreased lung function. Lower (FEV 1 /FVC) in adults with asthma was also reported.
The effects of weight loss on asthma control:
A couple of randomized studies reported by Rasmussen and Hanox in 2014 have revealed the positive impact of weight reduction on asthma symptoms and control. The first study was performed on obese asthmatic individuals revealed that weight loss improved lung function, symptoms, morbidity, and health status. Achieving these results could be through dietary weight reduction or by surgery. Thus an improvement in the airway responsiveness, lung volumes, systemic inflammatory markers and asthma severity and asthma control was observed after undergoing bariatric surgery in a follow-up period of 12 months. Whereas the other randomized study conducted, a 10-week dietary, exercise, or combined intervention, revealed that a 5–10% weight loss resulted in clinically important improvements in asthma control. Weight reduction results in improvement of asthma-related health outcomes in adults.[v]
In conclusion, it is evident that obesity is detrimental to asthma and affects asthma incidence, severity and control. The effects of obesity on lung function in asthmatic and non-asthmatic individuals observed could assist in the comprehension of asthmatic patients’ problems and eventually solving them. Obesity does have an undoubted negative impact on asthma severity and control and it requires the need for physicians to focus on obesity as a risk factor of asthma while treating obese asthmatic patients.
Medical awareness to obese asthmatic patients is a crucial part of the therapy plan as it will help the patient to understand his condition.
Hence individualizing treatment plans and providing a more patient centered management is an important step towards better patient outcomes, improving quality of life and help minimizing Emergency department visits and hospitalization on the long run.