© 2004 American Thoracic Society
Obesity and Asthma in ChildrenTo the Editor:Weiss and Shore, in their report on a workshop on obesity and asthma (1) referenced two of our articles (2, 3), which described analyses of data from the National Study of Health and Growth, a mixed longitudinal study of children aged 4–11 years from 1972–1994. The first article was a cross-sectional analysis of the association between asthma and body mass index (BMI) z-score. It did not examine "if obesity preceded the increase in asthma and wheezing" as stated by Weiss and Shore (1). It showed a strong association between asthma and BMI in the final period of data collection for more than 9,000 white children in the representative sample, and in girls in the multiethnic inner city sample. Weiss and Shore (1) criticized our second article "because it is primarily a repeated cross-sectional...analysis rather than a true longitudinal analysis, it did not use all the available data..." The main aim of the article was to investigate whether the increasing trend in BMI could explain that in the prevalence of asthma. In order not to mix this question with the separate question of whether, for the individual child, asthma attacks or wheeze varied in parallel with BMI, we included a maximum of one record per child. This was achieved by selecting a priori data for 8- and 9-year-old children from the biennial surveys from 1982–1994. We used the 1982–1994 data, as this was the period over which the trends were observed to be marked. As Weiss and Shore state correctly, there has been no other analysis of linked asthma and BMI data over time, and we found that no part of the trend in asthma was explained by the trend in BMI. This unexpected finding was because of the cross-sectional association between asthma and BMI being found only in recent years of the study. In a secondary analysis of a different selection of data, we showed a relationship between asthma or wheeze and BMI at age 9 or 10 years according to BMI categories at age 5 or 6 years, omitting those with disease reported at baseline. We therefore are puzzled why Weiss and Shore said that we "did not clearly show that BMI values actually antedated the asthma wheeze determinations." We hope that this clarifies any ambiguity.
King's College London London, United Kingdom FOOTNOTES Conflict of Interest Statement: S.C. does not have a financial relationship with a commercial entity that has an interest in the subject of this letter. R.J.R. received $1,000 in 2003 and $800 in 2004 for speaking at conferences sponsored by GlaxoSmithKline and Pfizer, respectively. REFERENCES
From the Authors: Drs. Chinn and Rona's interest in our workshop report (1) is appreciated. Their correction of our statement that their then second analysis was indeed longitudinal is also appreciated. Careful reading of their second article does suggest, however, that additional factors besides the statistical approach may have influenced their results. They studied 8- to 9-year-old children and examined incident asthma from this age onward, which could create a null bias in any relationship between body mass index (BMI) and incident disease in their cohort. This is because most childhood asthma is diagnosed before this age and, hence, elimination of these prevalent cases would be a null bias. Drs. Chinn and Rona also misquote our workshop report in saying that "there has been no other analysis of linked asthma and BMI data over time." There are now a number of studies in both adults and children, many of which are referenced in the workshop report, which clearly demonstrate that increases in BMI or birth weight are significant predictors of the development of asthma prospectively and independently of potential confounding factors, such as diet and physical activity (2–8). The majority of the epidemiologic evidence clearly suggests that BMI does influence asthma prevalence and morbidity. As Dr. Chinn herself has stated, there may be controversy about the relative magnitude of this association, and who is most at risk, but we can all agree that intervening on obesity should not await epidemiologic "proof" of the magnitude of this association (9). Further research also should not wait. The reason for the NHLBI Workshop was to stimulate this research effort to attempt to better understand the reasons for this important public health relationship.
a Brigham and Women's Hospital Boston, Massachusetts FOOTNOTES Conflict of Interest Statement: S.T.W. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. S.S. received $15,000 in 2002 from Merck and Co. to study the effects of IL-9 on airway smooth muscle. REFERENCES
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
