ArticlesAge of entry to day nursery and allergy in later childhood
Introduction
The prevalence of childhood allergies has increased during the past decades.1 One hypothesis is that a decline in exposure to infections early in life may be partly responsible for this trend.2, 3, 4 An inverse relation has been shown between some childhood infections and atopy in later life.5, 6, 7 Stimulation of Th1 lymphocytes by infections that may inhibit the expansion of allergen-specific Th2 lymphocytes at a critical time during early childhood could explain these results,8, 9 although lack of effect of early vaccination on the development of atopy is puzzling.10 Indirect evidence of an inverse relation between early childhood infections and allergies in later life comes from studies that reported an inverse relation between the number of siblings and allergic sensitisation.7, 11, 12 Siblings promote cross infections and this effect also takes place in day-care centres. Children who attend day nursery have more infections,13, 14, 15, 16 especially infections of the respiratory tract,17, 18, 19 than children who do not attend day nursery. If this infection hypothesis is true, children who attended day nursery should have fewer allergies in later life than children who did not. Comparisons between the two groups showed no differences in allergies or allergic sensitisation in schoolage children20 or in young adults.12 Why preschool nursery attendance does not seem to reduce the rate of atopy in later life is not known.21
An increase in the risk of respiratory illness associated with attendance at day nursery is most pronounced or even detectable if a child has no older siblings.22 Marbury and colleagues18 reported that the effect of day-care attendance on respiratory illness is stronger in firstborns than in those not born first. Therefore, a reduction in atopy associated with preschool nursery attendance might be detectable only in firstborns or in families with only one child.
We aimed to investigate the association between preschool attendance at day nursery and atopy in later life in a cross-sectional survey of children aged 5–14 years from eastern Germany.
Section snippets
Participants
Between September, 1992, and August, 1993, 2773 children from the towns of Zerbst, Bitterfeld, and Hettstedt in southern Sachsen-Anhalt, eastern Germany, were selected to take part in the study.23 There were three age-groups: 5–7 years (school entrants), 8–10 years (third grade), and 11–14 years (sixth grade). In Zerbst and Hettstedt, we enrolled all children in the three age-groups. In Bitterfeld, a random sample that represented a third of all schools and kindergartens (for school entrants)
Results
Data on family size and the exposure variable for age of entry to day nursery were known for 2430 children, 669 of whom were from small families and 1761 from large families. Table 1 shows the rate of allergy-related variables by age of entry to day nursery and by family size.
Among children from small families, all allergy-related variables showed an upward trend with older age at entry to day nursery. Exclusion of children with insufficient serum samples did not affect the results for
Discussion
Our findings show that in children aged 5–14 years from small families who entered day nursery at age 6–11 months, the prevalence of atopy was lower than in children who entered day nursery at an older age. There was no such association in children from large families.
Selection bias cannot explain these results. Even if the response to the study were associated with atopy, it is unlikely that this association would vary with age of entry to day nursery. Recall bias may have a role; parents who
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