In this large, population-based cross-sectional study, overweight, moderate obesity, and extreme obesity were associated with an increased frequency of asthma. Moderately and extremely obese youth had a 37% and 68% higher frequency of asthma, respectively. Several cross-sectional studies (4
) and prospective studies (5
) have reported associations between obesity, typically defined as > 95th percentile of BMI-for-age, and asthma in children. However, studies that examined the contribution of overweight to asthma risk yielded inconsistent findings, with some reporting a positive association (5
), and others reporting no association (8
); none specifically examined the role of extreme obesity.
In the 1996–2006, National Health and Nutrition Examination Survey (NHANES) population aged 2–19 years, Visness et al.
reported a prevalence of current asthma ranging from 9.0% to 10.7% per study year; the prevalence of current asthma for 2005–2006 was 10.7% (s.e. 0.5%), which is comparable to the estimated prevalence in our study (7
). These investigators also reported an adjusted OR for asthma risk of 1.32 (95% CI: 1.08–1.60) among overweight, and 1.68 (95% CI: 1.33–2.12) among obese youth (7
). These estimates are slightly higher than those described in this study, but may be due to the fact that NHANES assessed asthma status by self-report, included children from 2 years of age, and did not distinguish between moderate and extreme obesity (7
Results from our study also suggest that the magnitude of association between the degree of obesity and asthma substantially varies by race. Few studies have examined the association between increasing BMI and asthma within racial/ethnic groups, and results are inconsistent. Brenner et al.
found no association between obesity and asthma in 774 black adolescents (3
). However, the null finding in this study may be due to a small sample size, especially in the extreme ranges of BMI. Luder et al.
reported a significant association between increasing BMI and moderate to severe asthma among 1,017 black and Hispanic youth aged 6–13 (12
). Specifically, these investigators found that youth with asthma were 1.34 times as likely to be overweight, and 1.51 times as likely to be obese (12
); these estimates of association are relatively similar to those we report in our study. Despite our modest American Indian/Native Alaskan sample size (n
= 610), which limited our power to detect associations in some BMI groups, our findings of increased asthma prevalence among obese American Indian/Alaskan Native youth are highly consistent with a recent study conducted in 1,852 children from Northern Plains American Indian communities (28
). In this report, Noonan et al
. observed that overweight and obese youth were 1.72 times as likely to have current asthma compared to those of normal weight (28
), an estimate nearly identical to those we reported in our study for overweight and obese youth, respectively.
While some studies reported associations between increasing BMI and emergency department admission rates among youth with asthma (7
), others did not (29
). Our findings support the notion that extremely obese children and adolescents with asthma have greater health-care utilization, including both ambulatory and emergency room visits, than their normal weight counterparts. Other studies have reported higher number of asthma medications prescribed to overweight and obese youth with asthma compared to those of normal weight (12
). Our results also suggest that overweight, moderately obese, and extremely obese youth are more likely to be prescribed inhaled and oral steroids. Considered together, these findings may imply that obese youth are more symptomatic and/or have more severe asthma than normal weight youth with asthma.
We acknowledge that our cross-sectional design precluded us from assessing changes in asthma severity, which may be associated with obesity, or changes in body weight, which may be associated with asthma. Another limitation of our study is the lack of detailed information on specific asthma-related characteristics, such as wheezing and asthma attacks. Electronic health records did not include details on ethnic heritage, which would have allowed for further stratification among specific Hispanic subgroups known to have different asthma risks, or direct measures of lung function, such as forced vital capacity, forced expiratory volume, and forced expiratory flow rate which would also have allowed us to more accurately assess asthma status and severity. In addition, we were unable to control for certain environmental exposures or behaviors known to exacerbate asthma symptoms such as household smoking, pet dander, and air pollution, as well as physical activity or participation in sports.
Despite these limitations, our study has several strengths. Our population-based approach, combined with our large, multiethnic and diverse pediatric population, allowed us to examine a wide range of BMI within racial/ethnic groups that have not been previously investigated. While our American Indian/Native Alaskan sample was relatively small in size (n = 610), which limited our ability to detect modest associations between overweight and asthma, we were well powered to detect associations between extreme obesity and asthma, which were of larger magnitude. The high prevalence of extreme obesity, especially among racial/ethnic minorities, allowed for stable estimates of associations with high body weight in most minority groups. Additional strengths of the study include the availability of asthma diagnoses made by physicians rather than reliance on self-report, and the availability of asthma-specific prescription and health-care utilization information.
In conclusion, the findings of our study suggest that the association between increasing body mass and childhood asthma varies by race/ethnicity. Obesity, especially extreme obesity, may influence the prevalence of asthma in Asian/Pacific Islander and non-Hispanic white youth to a larger extent than in black or Hispanic youth. An increasing degree of obesity appears to further exacerbate asthma-related health-care utilization and treatment. Effective interventions are needed to target high risk populations in order to avoid medical emergencies among children with asthma.