Asthma: Obesity Is a Factor More in Girls than in Boys

Girls who are obese are more likely to also have asthma than are obese boys.

A study recently published in The Journal of Pediatrics gauged the relationship of physical fitness levels and obesity risk to asthma in adolescent boys and girls.

The study results pointed to several outcomes that diverged by sex, with obesity associated with greater prevalence of asthma in girls but not in boys, independent of fitness levels. At the same time, higher fitness levels were associated with reduced asthma morbidity in boys but not girls, regardless of weight considerations.

The cross sectional assessment, led by Kim D. Lu MD, and colleagues, a pediatric pulmonologist in the Department of Pediatrics, UC Irvine Medical Center, Orange, CA, examined data from the 1999-2004 National Health and Nutrition Examination survey. The study group comprised of 4828 adolescents between 12-19 years of age.

Participants who had been previously identified as asthmatic by a doctor or health professional answered a series of follow-up questions on their current asthma status, asthma attacks and asthma-related ED visits in the prior 12 months, and wheezing history. They were further assessed for BMI and cardiorespiratory fitness status.

Cardiorespiratory fitness was assessed through a multi-stage treadmill exercise with the goal of achieving a heart rate around 75% of age-predicted maximum (220- age) by the 2^nd exercise stage. A series of logistic regression models were employed to assess sex-specific associations of BMI and fitness with asthma prevalence and morbidity.

The data demonstrated significant relationships between overweight/obesity status in girls and increased asthma prevalence, history of asthma, and current asthma (aOR 1.73, 95% CI 1.13-2.64).

None of these associations was found for boys. Overweight/obese girls also showed significantly increased odds of asthma attacks and exercise-related wheezing (while boys did not).

Examining the roles of fitness levels, high fitness among boys — though not girls - was associated with significantly decreased odds of asthma morbidity.

Compared with low/moderately fit boys, for example, the high fit boys had significantly lower odds of asthma-related ED visits (aOR 0.24, 95% CI 0.07-0.88), and decreased wheezing-related measurements (e.g. missed days, ED visits).

The authors noted that, while indicating mixed results, most prior studies in this area “support a more consistent relationship between obesity and asthma development in girls,” — but not in boys - as suggested by the present study.

The authors also note, however, that the significantly divergent effect of high fitness levels on asthma status between girls and boys are not in accord with some other study findings, and emphasize the need for future studies that use “more objective measures including cardiorespiratory fitness testing and spirometry in a pediatric population with asthma.”