DETROIT-- Poverty isn't the only reason black children have greater asthma morbidity and mortality than white children do. Physiologic differences--specifically, reduced lung function and higher immunoglobulin E (IgE) levels--may contribute to increased asthma severity in black children.

That was the finding of researchers who studied 569 children age 6 to 8 years, 14% of whom were black.[1] "Our study was unique because the African American children were from a middle class suburban area," lead author Christine Joseph, PhD, told RESPIRATORY REVIEWS. Black children in previous pediatric asthma studies typically came from poor urban areas.

By enrolling black and white children from the same middle-class suburb, the researchers hoped to minimize the influence of socioeconomic status. Low socioeconomic status increases the risk of asthma morbidity and mortality because the poor often have little or no access to quality health care.

Data were drawn from two studies of children in suburban Detroit--the Childhood Allergy Study and the Southfield Childhood Allergy Study. Subjects included children categorized as African American or European American. "The children in the latter group were essentially Caucasian," noted Dr. Joseph, a senior epidemiologist in the Department of Biostatistics and Research Epidemiology at the Henry Ford Health System in Detroit.

All subjects underwent a clinical assessment consisting of a medical history and physical examination, allergen skin testing, spirometry, methacholine challenge, and measurement of total and allergen-specific IgE. A subject was classified as asthmatic if a parent reported that the child had ever received an asthma diagnosis from a physician. Asthma prevalence was 10% in both groups, though fewer black children met the criteria for current asthma--a physician's diagnosis and asthma symptoms in the past 12 months.

HIGHER IgE LEVELS

The geometric mean serum total IgE level was higher in black than in white children (60.63 IU/mL vs 27.48 IU/mL). Also, the serum IgE level correlated with methacholine reactivity in white children but not in black children. "To our knowledge, this apparent racial difference in the relationship between total IgE and airway reactivity has not been previously reported," the study authors explained.

Baseline pulmonary function was markedly lower in black children. Only about three quarters of the black children, versus nearly all of the white children, had a forced expiratory volume in one second of at least 70% of predicted. This racial difference persisted after further adjustment for age, gender, education, parental smoking, and maternal smoking during pregnancy. Black children also had a significantly smaller forced vital capacity. Furthermore, they were markedly more likely than white children to react to methacholine challenge (41.7% vs 22.3%).

Baseline pulmonary function was markedly lower in black children. Only about three quarters of the black children, versus nearly all of the white children, had a forced expiratory volume in one second of at least 70% of predicted. This racial difference persisted after further adjustment for age, gender, education, parental smoking, and maternal smoking during pregnancy. Black children also had a significantly smaller forced vital capacity. Furthermore, they were markedly more likely than white children to react to methacholine challenge (41.7% vs 22.3%).

The researchers did not find racial differences when testing for sensitization to major indoor allergens, including cockroaches. However, they did find that black children were more likely than white children to be sensitized to ragweed and grass. These findings support the hypothesis that black children may be predisposed to asthma.

--Timothy Begany

Reference
1. Joseph CLM, Ownby DR, Peterson EL, Johnson CC. Racial differences in physiologic parameters related to asthma among middle-class children. Chest. 2000;117:1336-1344.