© 2004 American Thoracic Society
Less Childhood Obesity—Less Persistence of Wheeze in Teenage Girls and Boys?Brigham & Women's Hospital Boston, Massachusetts From the longitudinal Tucson Children's Respiratory Study, Guerra and colleagues (1) report in this issue of the Journal (pp. 78–85) that 58% of children with frequent wheeze, and 30% of children with infrequent wheeze in the school-aged years before puberty, had wheezing that persisted after puberty. These results are comparable to the longitudinal New Zealand birth cohort study that followed children from birth to 26 years of age (2), in which more than 25% of children had wheezing that persisted from childhood to adulthood or that relapsed after remission. The Tucson findings provide a cautionary message for clinicians, who should not necessarily expect patients' asthma to remit when they reach their teens. Because overweight and obesity increased the risk of persistent wheeze, their findings also provide additional rationale for pediatricians to follow National Academy of Pediatrics Guidelines (3), encouraging children to develop dietary and activity patterns that decrease the risk of obesity. But despite its longitudinal study design, this report does not pinpoint at what stage of development obesity began, whether potentially modifiable behaviors (4) preceded development of obesity, and whether the teen obesity–wheeze relationship was the same for girls and boys. Cross-sectional studies and longitudinal studies from English-speaking countries (2, 5, 6) suggest that the course of asthma and wheeze is different for girls than for boys (7). In early childhood, up until the teen years, prevalence and incidence of asthma are higher in boys than in girls. In the teen years, the incidence rate in girls increases, and by adulthood women have higher asthma rates than men (6). Female sex as well as sensitization to house dust mites, smoking, airway hyperresponsiveness, and early onset of wheeze predicted persistence or relapse of wheeze in the longitudinal New Zealand birth cohort study (2). Girls had higher rates of unremitting wheeze in the Tucson study, but the investigators report that they had insufficient power to evaluate whether sex modified the effects of obesity or age of puberty on wheeze/asthma persistence. In an earlier Tucson study report (8), girls, not boys, who became overweight or obese between 6 and 11 years of age were 7 times more likely to develop new asthma symptoms between ages 11 and 13 years, with significantly more peak flow variability and bronchodilator responsiveness. Wheeze rates were not higher in girls or boys who already had established overweight or obesity by age 6 years. In contrast, in girls from the longitudinal Six Cities study of 9,828 children aged 6 to 14 (9), both increased body mass index at entry to the study and greater increases in body mass index during follow-up were associated with increased risk of new diagnosis of asthma with wheeze. Early age of puberty onset was also associated with increased risk of persistent wheeze in this Tucson report by Guerra and coworkers (1). It is not surprising that the association of female sex with increased risk of asthma persistence disappeared with adjustment of age of onset of puberty, because age of onset of puberty is so correlated with female sex. On average, girls begin to develop pubic hair before age 12 years, more than a year before boys (10). What is early puberty for boys may be normal age of puberty for girls. Just as the percent predicted values for lung function are sex-specific, the puberty results might have been easier to interpret had the investigators done sex-specific classification of whether puberty was early before combining the data for girls and boys. In addition, we may have less confidence in classification of age of puberty onset in boys compared with that of girls if the mothers were the primary reporters of when their sons or daughters first developed the earliest signs of puberty.
To make life more complicated, early puberty may be related to obesity, and that relationship may be different for girls and boys. Early puberty is a period of relative insulin resistance (11). Higher body mass index in the prepubertal years predicted earlier menarche in girls in New Zealand (12) and U.S. longitudinal studies (13). The potential biologic mechanisms for the association of overweight with persistence of asthma symptoms have been extensively reviewed (14). Overweight or obesity may contribute to persistence of asthma because of pulmonary mechanics; a relationship to chronic systemic non-IgE (e.g., interleukin-6; tumor necrosis factor- In the new age of genomics, a goal is to design therapies for disease that are increasingly individualized. There is no question that both obesity and asthma involve, in part, inherited traits. Research to identify genetically at-risk children who might benefit most from early intervention is one goal (3). But strategies to reduce teen wheeze by reducing childhood obesity will require social as well as individualized approaches. The National Academy of Pediatrics recommends working with communities and schools to enhance physical activity opportunities and decrease availability of foods with little nutritional value (3). The success of these recommended community approaches to reduce obesity or persistence of wheeze needs to be formally evaluated. Whereas primary prevention in pregnancy or early childhood may optimize establishment of normal growth patterns, the results of the Tucson study suggest that reduction of obesity (or its associated behaviors) in school-aged years may also protect against chronic wheeze. FOOTNOTES Conflict of Interest Statement: D.R.G. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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