Asthma and obesity connection surprises public health researchers
Overweight inner-city minority kids are at high risk
Harvard researchers have noticed the obese children in their studies were more likely to be diagnosed with asthma. That observation raises the possibility that weight control could prevent the onset of asthma or even ease the severity of the disease among children who already have it.
Carlos Camargo, MD, DrPH, assistant professor, physician and research epidemiologist at Brigham and Women’s Hospital and Harvard Medical School in Boston, theorizes there is a distinct form of the disease he calls "obesity-induced asthma."
In his ongoing research, Camargo also suggests patients with this form of the disease may have different responses to medications and therapies than other patients with asthma. He presented the findings at the American Lung Association/American Thoracic Society International conference in San Diego in late April.
Other researchers have recently published studies on the correlation between obesity and asthma with some slightly different twists.
Two major questions are left unanswered:
Does obesity cause asthma or are asthmatic kids less likely to exercise, increasing their chances to become obese? Would losing weight prevent the onset of asthma in those at risk or lessen the effects of the disease in those already affected?"The link between asthma and obesity is something that is not well known in the field. We just stumbled across it," says Leonard H. Epstein, PhD, professor of psychology and nutrition at the State University of New York in Buffalo. "We noticed over time that kids who couldn’t join exercise programs because of the severity of their asthma were much more likely to be obese."
Epstein thinks obesity among asthmatic children is coupled with reluctance to exercise, fear that exercise will bring on an asthma episode, and parental belief that children with asthma should not exercise.
In a similar study conducted by Elisabeth Luder, PhD, associate professor of pediatrics at Mount Sinai School of Medicine and co-director of the Pediatric Pulmonary Center in New York, there seemed to be a connection between severe asthma symptoms and patient obesity.
None of the children in any of the studies were taking oral steroids, which would have accounted for weight gain.
Chicken or egg?
Which comes first — the obesity or the asthma? Luder was uncertain at the conclusion of her study. "In my mind, the obesity problems probably came first, followed by the asthma. Obesity related to asthma may turn out to have a different cause. We just don’t know yet."
"The sedentary nature of fat people affects breathing, and there may be some connection between fatty accumulation around the neck and airway compression," she says.
Luder’s study, published last year in the Journal of Pediatrics involved 209 black and Hispanic children in the poor South Bronx neighborhood of New York.
Her team found that obese children with moderate to severe asthma who attended an ambulatory chest clinic in the inner city medical center were significantly more likely to miss school, have poor peak expiratory flow rates, and need more medications than children of normal weight with similar asthma severity.
Citing evidence collected elsewhere through NHANES III (the third National Health and Nutrition Examination Survey) that suggests asthma may predispose children to gain weight by limiting their physical activity, Luder theorizes that being overweight may exacerbate the symptoms of asthma through a direct effect on pulmonary function. (NHANES III is a study conducted by the National Institute of Diabetes and Digestive and Kidney Disease in Bethesda, MD.)
Camargo’s paper is based on the study of 16,862 children of women who participated in the Nurses Health Study. His findings were similar to those of Luder and Epstein: The prevalence of asthma was 40% higher in children in the highest quintile of body mass index (BMI) than in those in the lowest quintile; the risk of asthma increased as the children became heavier. (See copy of BMI chart, p. 63.)
In addition, Camargo’s group found the rate of new asthma diagnoses more than doubled in the heaviest children.
"This study suggests that obesity may explain some of the increase in asthma in Western countries in the last 20 years," he says. "It’s interesting to note that in wealthier countries, the poorest people are the most likely to be obese and the most likely to have asthma, supporting the plausibility of the relationship between the two conditions."
Although very little research has yet been done to examine how obesity might lead to asthma, Camargo agrees with Luder’s speculation that being overweight somehow compresses the airways, making them smaller and therefore more reactive to pets and other common asthma triggers.
"Asthma is a somewhat vague term for a variety of disorders that manifest with episodic wheezing," Camargo says. "Some are clearly related to exposure to allergens [such as cat hair], others to exposure to irritants [e.g. perfume], others to obesity. This is entirely speculative but, I think, a reasonable starting point for investigation."
Epstein says he believes asthma is more likely to cause obesity in some patients rather than the other way around. In a study of 178 urban minority children published in the December 1998 issue of the Archives of Pediatric Adolescent Medicine, Epstein and his colleagues found that compared to the control group, 30.6% more of the children with asthma were very obese. In this study, severe obesity was defined as the 95th percentile of BMI.
"It makes sense to us that asthma can influence physical activity, since activity is such a tremendously powerful means of increasing lung function," says Epstein.
"Parental fear that their children will aggravate their condition through exercise is a major factor in the failure of kids with asthma to engage in physical activity," he says, because "parents have such a strong influence on their kids’ lives and they set up a pattern of that fear that can last a lifetime."
In a new and not-yet-published study, Epstein says even though asthma is more prevalent in minority children in poor inner-city neighborhoods, the results show the obesity-asthma link is not related to ethnic group or socioeconomic status.
He recommends that physicians and clinicians "pay careful attention" to the weight of young patients at risk for asthma and "get aggressive about weight loss" with any patient who reaches the 85th percentile, whether or not there are signs of asthma.
Luder adds that children in her clinic found their asthma symptoms were eased if they ate a high-protein diet, even when they lost only a few pounds.
Some experts suggest that diets high in fish, omega-3 fatty acids, and grain as well as fruits with high amounts of vitamin A and C all tend to help protect against asthma, Luder says.
In addition, she observed the children on a weight-loss plan were more compliant in taking their medications and experienced improvement in their condition because of better adherence to their management plans. It’s going to take more research to determine why this seems to be true, she says.
[Carlos Camargo can be reached at (617) 432-1000, Leonard Epstein at (716) 645-6315, and Elisabeth Luder at (212) 241-6500.]
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