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Does exposure of young children to older siblings or to children at day-care facilities protect against the development of asthma later in childhood?
BACKGROUND: Asthma is the most common chronic disease of childhood in the United States and has increased dramatically in incidence and prevalence over the last 30 years. One hypothesis invokes the inverse relationship between the frequency of some allergic disorders and both childhood infections and the number of siblings. Children attending day-care have more infections, and this may have a similar protective effect.
POPULATION STUDIED: A total of 1246 newborns were enrolled in the Tucson Children’s Respiratory Study between 1980 and 1984. All newborns were healthy and were cared for by pediatricians of a large health maintenance organization in Tucson.
STUDY DESIGN AND VALIDITY: The parents of 1035 newborns completed at least1 questionnaire and were included in a cross-sectional analysis. The parents of 875 children (83%) completed at least 1 questionnaire and provided information on day-care attendance, and these were included in a longitudinal study. Information was obtained from parents of enrolled children on the number of siblings at home, day-care attendance in the first 3 years of life, the diagnosis of asthma, and frequent wheezing at the ages of 6, 8, 11, or 13 years. Children were categorized as having asthma if they had a diagnosis of asthma in the previous year. Children with scores of 2 or higher on a wheezing frequency scale from 1 to 5 at 2 or 3 years were defined as having frequent wheezing. Skin test reactivity to common allergens in the Tucson area and serum immunoglobulin E were measured at 6 and 11 years as a biological marker of allergic disease. The analysis accounted for potential confounding variables including sex, a history of asthma in either parent, race of parents, mother’s level of education, mother’s smoking status during the prenatal period, and breastfeeding status. Study participants were more likely to have 1 or no siblings, a mother with a high level of education, and white parents than those who were excluded or refused to participate. The retrospective nature of the questionnaires may have led to some misclassification. Although follow-up was very good, the study may not be generalizable to other ethnic groups or practices in different geographic locations.
OUTCOMES MEASURED: The primary outcome was the development of asthma and frequent wheezing in childhood as related to day-care attendance and exposure to siblings.
RESULTS: The incidence of asthma among children with 2 or more older siblings or who attended day-care before 6 months was significantly lower than that among children who had one or no older siblings and no day-care (relative risk [RR]=0.6; 95% confidence interval [CI], 0.4-0.8; P=.002). In multivariate analysis, there was an inverse association of each additional sibling (adjusted RR=0.8; 95% confidence interval, 0.7-1.0; P=.04) and attendance at day-care at younger than 6 months of age (adjusted RR=0.4; 95% CI, 0.2-1.0; P=.04) with the development of asthma. Frequent wheezing at the age of 2 years was more likely in children with exposure to more siblings or to day-care (adjusted RR=1.4; 95% CI, 1.1-1.8; P=.01). Those children with greater exposure were less likely to have frequent wheezing from the age of 6 years (adjusted RR=0.8; 95% CI, 0.6-1.0; P=.03) through the age of 13 years (adjusted RR=0.3; 95% CI, 0.2-0.5; P <.001). Male sex (adjusted RR=1.5; 95% CI, 1.1-2.0; P=.02) and a history of asthma in the mother (adjusted RR=2.3; 95% CI, 1.6-3.3; P <.001) or father (adjusted RR=1.6; 95% CI, 1.1-2.4; P=.02) were positively associated with development of asthma in the child.
Exposure of young children to older siblings or to children in day-care facilities may be protective against development of asthma and wheezing later in childhood, even though they may have more frequent wheezing in the preschool years.
BACKGROUND: Asthma is the most common chronic disease of childhood in the United States and has increased dramatically in incidence and prevalence over the last 30 years. One hypothesis invokes the inverse relationship between the frequency of some allergic disorders and both childhood infections and the number of siblings. Children attending day-care have more infections, and this may have a similar protective effect.
POPULATION STUDIED: A total of 1246 newborns were enrolled in the Tucson Children’s Respiratory Study between 1980 and 1984. All newborns were healthy and were cared for by pediatricians of a large health maintenance organization in Tucson.
STUDY DESIGN AND VALIDITY: The parents of 1035 newborns completed at least1 questionnaire and were included in a cross-sectional analysis. The parents of 875 children (83%) completed at least 1 questionnaire and provided information on day-care attendance, and these were included in a longitudinal study. Information was obtained from parents of enrolled children on the number of siblings at home, day-care attendance in the first 3 years of life, the diagnosis of asthma, and frequent wheezing at the ages of 6, 8, 11, or 13 years. Children were categorized as having asthma if they had a diagnosis of asthma in the previous year. Children with scores of 2 or higher on a wheezing frequency scale from 1 to 5 at 2 or 3 years were defined as having frequent wheezing. Skin test reactivity to common allergens in the Tucson area and serum immunoglobulin E were measured at 6 and 11 years as a biological marker of allergic disease. The analysis accounted for potential confounding variables including sex, a history of asthma in either parent, race of parents, mother’s level of education, mother’s smoking status during the prenatal period, and breastfeeding status. Study participants were more likely to have 1 or no siblings, a mother with a high level of education, and white parents than those who were excluded or refused to participate. The retrospective nature of the questionnaires may have led to some misclassification. Although follow-up was very good, the study may not be generalizable to other ethnic groups or practices in different geographic locations.
OUTCOMES MEASURED: The primary outcome was the development of asthma and frequent wheezing in childhood as related to day-care attendance and exposure to siblings.
RESULTS: The incidence of asthma among children with 2 or more older siblings or who attended day-care before 6 months was significantly lower than that among children who had one or no older siblings and no day-care (relative risk [RR]=0.6; 95% confidence interval [CI], 0.4-0.8; P=.002). In multivariate analysis, there was an inverse association of each additional sibling (adjusted RR=0.8; 95% confidence interval, 0.7-1.0; P=.04) and attendance at day-care at younger than 6 months of age (adjusted RR=0.4; 95% CI, 0.2-1.0; P=.04) with the development of asthma. Frequent wheezing at the age of 2 years was more likely in children with exposure to more siblings or to day-care (adjusted RR=1.4; 95% CI, 1.1-1.8; P=.01). Those children with greater exposure were less likely to have frequent wheezing from the age of 6 years (adjusted RR=0.8; 95% CI, 0.6-1.0; P=.03) through the age of 13 years (adjusted RR=0.3; 95% CI, 0.2-0.5; P <.001). Male sex (adjusted RR=1.5; 95% CI, 1.1-2.0; P=.02) and a history of asthma in the mother (adjusted RR=2.3; 95% CI, 1.6-3.3; P <.001) or father (adjusted RR=1.6; 95% CI, 1.1-2.4; P=.02) were positively associated with development of asthma in the child.
Exposure of young children to older siblings or to children in day-care facilities may be protective against development of asthma and wheezing later in childhood, even though they may have more frequent wheezing in the preschool years.
BACKGROUND: Asthma is the most common chronic disease of childhood in the United States and has increased dramatically in incidence and prevalence over the last 30 years. One hypothesis invokes the inverse relationship between the frequency of some allergic disorders and both childhood infections and the number of siblings. Children attending day-care have more infections, and this may have a similar protective effect.
POPULATION STUDIED: A total of 1246 newborns were enrolled in the Tucson Children’s Respiratory Study between 1980 and 1984. All newborns were healthy and were cared for by pediatricians of a large health maintenance organization in Tucson.
STUDY DESIGN AND VALIDITY: The parents of 1035 newborns completed at least1 questionnaire and were included in a cross-sectional analysis. The parents of 875 children (83%) completed at least 1 questionnaire and provided information on day-care attendance, and these were included in a longitudinal study. Information was obtained from parents of enrolled children on the number of siblings at home, day-care attendance in the first 3 years of life, the diagnosis of asthma, and frequent wheezing at the ages of 6, 8, 11, or 13 years. Children were categorized as having asthma if they had a diagnosis of asthma in the previous year. Children with scores of 2 or higher on a wheezing frequency scale from 1 to 5 at 2 or 3 years were defined as having frequent wheezing. Skin test reactivity to common allergens in the Tucson area and serum immunoglobulin E were measured at 6 and 11 years as a biological marker of allergic disease. The analysis accounted for potential confounding variables including sex, a history of asthma in either parent, race of parents, mother’s level of education, mother’s smoking status during the prenatal period, and breastfeeding status. Study participants were more likely to have 1 or no siblings, a mother with a high level of education, and white parents than those who were excluded or refused to participate. The retrospective nature of the questionnaires may have led to some misclassification. Although follow-up was very good, the study may not be generalizable to other ethnic groups or practices in different geographic locations.
OUTCOMES MEASURED: The primary outcome was the development of asthma and frequent wheezing in childhood as related to day-care attendance and exposure to siblings.
RESULTS: The incidence of asthma among children with 2 or more older siblings or who attended day-care before 6 months was significantly lower than that among children who had one or no older siblings and no day-care (relative risk [RR]=0.6; 95% confidence interval [CI], 0.4-0.8; P=.002). In multivariate analysis, there was an inverse association of each additional sibling (adjusted RR=0.8; 95% confidence interval, 0.7-1.0; P=.04) and attendance at day-care at younger than 6 months of age (adjusted RR=0.4; 95% CI, 0.2-1.0; P=.04) with the development of asthma. Frequent wheezing at the age of 2 years was more likely in children with exposure to more siblings or to day-care (adjusted RR=1.4; 95% CI, 1.1-1.8; P=.01). Those children with greater exposure were less likely to have frequent wheezing from the age of 6 years (adjusted RR=0.8; 95% CI, 0.6-1.0; P=.03) through the age of 13 years (adjusted RR=0.3; 95% CI, 0.2-0.5; P <.001). Male sex (adjusted RR=1.5; 95% CI, 1.1-2.0; P=.02) and a history of asthma in the mother (adjusted RR=2.3; 95% CI, 1.6-3.3; P <.001) or father (adjusted RR=1.6; 95% CI, 1.1-2.4; P=.02) were positively associated with development of asthma in the child.
Exposure of young children to older siblings or to children in day-care facilities may be protective against development of asthma and wheezing later in childhood, even though they may have more frequent wheezing in the preschool years.