Michael B. Foggs, MD Chief of Allergy and Immunology Advocate Health Centers Advocate Professional Group Advocate Health Care Chicago, Illinois

Asthma and obesity are common disorders that significantly affect public health. Evidence for a link between the two continues to grow, with an increase in asthma prevalence reported throughout the world for overweight adults and children.¹ In 2007, a meta-analysis of 7 prospective epidemiologic studies linked elevated BMI (= 25) with a dose-dependent increase in the odds of incident asthma in both men and women.²

Who is most at risk? Although the association between asthma and excess body weight has been well documented, the nature of the link appears to differ in adults vs. children, males vs. females, and allergic vs. nonallergic individuals.

In a large cross-sectional study published in 2006, obesity was more strongly associated with asthma in women.³ In this study of 86,144 Canadian adults, 1 unit of increased BMI was associated with an approximate 6% increase in asthma risk in women and a 3% increase in men.

The association between obesity and asthma was significantly stronger in nonallergic women than in allergic women
(P < 0.001) but not significantly different in nonallergic vs. allergic men.

A recent prospective study of 4393 children followed for 14 years showed that the relation between BMI and incident asthma also varied by sex.⁴ However, this time, boys with high body masses (= 85th percentile at age 2-3 years) had an increased risk for developing asthma when compared with girls (hazard ratios 1.6 vs. 0.8). These results suggest that obesity is a risk factor for asthma during early childhood—the time when most asthma develops.

Focusing on control. Asthma "control" is a central theme of newly issued asthma guidelines.⁵ However, achieving this control may be more difficult in patients who are overweight or obese.⁶ In a recent study of 406 patients,
overweight (BMI = 25) individuals were significantly less likely to transition from unacceptable to acceptable
control (P < 0.01).⁶

Clearly, weight control should play a role in the management of obese asthma patients. In adults, studies to date have shown associations of weight loss with improvements in asthma symptoms, lung function, hospitalizations, and medication use.¹ Although the effect of weight control on childhood asthma has not been established, evidence suggests that weight management early in life may also play a role in lowering the incidence of childhood asthma.⁴

Looking ahead. Research on the relationship between obesity and asthma is ongoing and may lead to additional therapeutic strategies for treating individuals with both conditions. Several possible mechanisms are under study,1 including common etiologies and genetic factors, shared comorbidities (eg, gastroesophageal reflux disease), mechanical factors (eg, rapid shallow breathing patterns), and the effects of adipokines such as interleukin (IL)-6, monocyte chemotactic protein (MCP)-1, and tumor necrosis factor a (TNFa). A better understanding of the pharmacokinetics of asthma medications in obese patients may also help clinicians finely tune their strategies for control.

References

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