Does Obesity Cause or Worsen Asthma? How Does Obesity Affect Asthma?

Obesity is an important public health issue. Experts estimate that 30% of the U.S. population is obese and an additional 35% is overweight. Moreover, the obesity rate is rising steadily according to the U. S. Centers for Disease Control and Prevention (CDC).

Obesity is a known risk factor for cardiovascular disease, diabetes, and certain types of cancer. Scientific evidence is suggesting that obesity and asthma are interrelated. Epidemiological data suggest that obesity and being overweight are risks factor for asthma.

Although the causality of asthma by obesity has not been established, research studies support the idea that there may be some relationship between the two conditions. The first report related asthma and obesity was published in 1986. However, the interest of the medical community about this issue started in the mid-nineties. After 1999, more than 30 studies on this issue have been reported. In 27 of these results show an increased prevalence of asthma in the obese and/or overweight people.

The largest prospective followed more than 135,000 men and women in Norway for more than 21 years! According to this large-scale prospective study, the incidence of asthma increased steadily at 1% for each unit of Body Mass Index (BMI), beginning at 22 for men. For women, beginning at BMI of 22, there is a 7% increase in asthma incidence per BMI Unit increase.

How does Obesity Affect Asthma?

There are many possible mechanisms by which obesity could be a risk factor in the development or worsening of asthma disease including: gastroesophageal reflux, complications from breathing problems (low lung volume, altered pattern of breathing , sleep-disordered breathing), chronic systemic inflammation, and endocrine factors.

Animal models may provide some directions on how obesity affects asthma. For example Ob/ob mice (obese mice) have small lung mass compared to normal mice. Obesity in these animals impacts the lung anatomy, airway branching structure, and the nature or distribution of connective tissue, all factors that may affect breathing and thus, enhance asthma symptoms.

Chronic systemic inflammation may be another mechanism causing obesity. It is known that obese people have a state of chronic, low-grade systemic inflammation. Inflammation of the respiratory tissue may cause edema which in turn may cause or worsen asthma symptoms.

The exact reason of why asthma is affected by obesity is not known. However, several biological processes experienced by obese patients may lead to the development or worsening of asthma. Knowing these mechanisms may be the basis for new therapeutic treatments for an increasingly susceptible part of the population (the obese and overweight).

References:

CDC 2010 (www.cdc.gov/nccdphp/dnpa/obesity/trend/index.htm).

Nystad, W., Meyer, H. E., Nafstad, P., Tverdal, A., & Engeland, A. Body mass index in relation to adult asthma among 135,000 Norwegian men and women. 2004. American Journal of Epidemiology, 160, 969–976.