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Asthma and Obesity

According to a study by the CDC, obese adults were 66% more likely than adults of normal weight to have asthma (1). Other studies have found that women who gained weight after age 18 had an increased risk of developing asthma (2) and that female reproductive hormones may contribute to the onset of asthma among adult women (3).

Another study showed that while obesity is a risk factor for self-reported asthma, many more obese than non-obese subjects were using bronchodilators despite a lack of objective evidence for airflow obstruction (e.g. pulmonary function tests). This suggests that causes other than airflow obstruction are responsible for the onset of shortness of breath in obesity, and that asthma might be overdiagnosed in the obese population (4).

Childhood asthma and obesity have risen in tandem over the last 20 years, but the nature of that relationship remains vague. A high, not low, birth weight has been found to be a risk factor for increased emergency visits for asthma during childhood (5). A large Canadian study found there was no statistical association between obesity and asthma among children age 4 to 11 years (6). In a study of U.S. inner-city children with asthma, obese children used more medicine, wheezed more, and a greater proportion had unscheduled ED visits than thinner children (7).

Some potential explanations for the apparent link between asthma and obesity that require further research include: insulin resistance, gastroesophageal reflux disease (GERD) as a result of obesity, physical inactivity promoting both obesity and asthma, and diet. There may be no causal connection between the two conditions, and more research is needed to complete this complex puzzle.

(1) Risk factors for asthma in US adults: results from the 2000 Behavioral Risk Factor Surveillance System. Gwynn RC, J Asthma, 2004 Feb;41(1):91-8.

(2)Prospective Study of Body Mass Index, Weight Change, and Risk of Adult-onset Asthma in Women. Camargo, CA et al, Arch Intern Med, 1999;159:2582-2588.

(3) Prospective Study of Postmenopausal Hormone Use and Newly Diagnosed Asthma and Chronic Obstructive Pulmonary Disease. Barr RG et al , Arch Intern Med .  2004;164:379-386.

(4) Obesity is a risk factor for dyspnea but not for airflow obstruction. Sin DD, et al, Arch Intern Med. 2002 Jul 8;162(13):1477-81.

(5) The relationship between birth weight and childhood asthma: a population-based cohort study. Sin DD, et al, Arch Pediatr Adolesc Med. 2004 Jan;158(1):60-4.

(6) Is obesity associated with asthma in young children? To T, et al, J Pediatr. 2004 Feb;144(2) :162-8.

(7) Do obese inner-city children with asthma have more symptoms than nonobese children with asthma?  Belamarich PF et al, Pediatrics. 2000 Dec;106(6):1436-41.

From the Summer 2004 AIM newsletter, author: Michael Cabana, MD, MPH