Purpose of the Study. Recent cross-sectional studies have shown an association between obesity and an increased risk of asthma, especially in females. These authors used data from the Tucson Children’s Respiratory Study to search for an increase in asthma in children who became overweight between 6 and 11 years of age.
Study Population. The participating children are a birth cohort enrolled between 1980 and 1984 and followed longitudinally. All are resident in the Tucson, Arizona, area.
Methods. Symptom questionnaires were completed by parents when the children were 6, 8, 11, and 13 years of age. Weight and height were measured at age 6 and 11. Home peak flow readings were gathered at age 11. Only those children providing peak flow measurements twice daily on at least 4 days over 1 week were included in the analysis. Spirometry including bronchodilator response was also obtained at age 11.
Results. By age 6 and 11 years, 55% and 48%, respectively, of the original cohort remained in the study. Several factors were associated with a body mass index (BMI) in the overweight (BMI >85 percentile to <95 percentile) or obese (BMI >95 percentile) range. Females who were overweight or obese at the age 11 visit were more likely to have a concurrent history of wheezing than the nonoverweight. This effect was not present in girls at age 6 nor in boys at either age. Females who became overweight or obese between age 6 and 11 were roughly 7 times more likely to have developed new-onset asthma at age of 11 or 13. This history of wheezing was accompanied by an increase in peak flow variability and bronchodilator responsiveness. This association of obesity with new-onset asthma between 6 and 13 years was seen in the boys.
Conclusions. The authors conclude that development of an elevated BMI between age 6 and 11 is associated with an increased risk of asthma in girls. They speculate that there are 2 likely explanations for the observation. First, obesity may influence circulating female sex hormones; these hormones are thought to alter beta2-adrenergic responsiveness and may have other proasthmatic activity. A second possibility is the presence of a subgroup of girls with genetic alterations in the responsiveness of female hormone receptor(s). Such a change could lead to a predisposition to obesity and to asthma symptoms. The authors note a third possibility, a relationship of lack of exercise and increased risk of asthma and obesity, that cannot be addressed by the data available.
Reviewer’s Comments. More risk factors for asthma continue to come to light. Certainly the risks are not all allergic, nor are they even all restricted to obvious links to the immune system. Now to the allergic risks, we might add the risks of cleanliness (the hygiene hypothesis), small sibships, and obesity. For early-life wheezing, there’s the risk of viral infection, but for later-life wheezing these infections may be protective. Perhaps we will really understand all this in another couple of decades.
- Copyright © 2002 by the American Academy of Pediatrics