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Family structure, neonatal infection, and hay fever in adolescence
D P Strachan1, E M Taylor, R G Carpenter
1Department of Public Health Sciences, St George's Hospital Medical School, London.
Insights
Increased siblings and early life infections may protect against allergic sensitization, particularly hay fever. Larger families and more older siblings were associated with reduced hay fever risk in children.
Area of Science:
- Immunology
- Epidemiology
- Allergy Research
Background:
- Allergic sensitization, a key factor in conditions like hay fever, is influenced by environmental exposures in early life.
- The hygiene hypothesis suggests reduced exposure to microbes may increase allergy risk.
Purpose of the Study:
- To investigate the protective effects of sibling numbers and early life infections against allergic sensitization.
- To explore the relationship between family structure, infant feeding, and the development of hay fever.
Main Methods:
- A historical cohort study involving 11,765 children aged 11-16 years in Sheffield, UK.
- Data collection included questionnaires on family structure and hay fever history, health visitor records for neonatal illness, and skin prick testing for grass pollen sensitization in a subset of children.
Main Results:
- Hay fever prevalence was significantly lower in children from larger families and those with more older siblings.
- Exclusive breastfeeding in the first month was linked to a higher risk of hay fever.
- Children at high risk due to family structure were more likely to be sensitized to grass pollen.
Conclusions:
- Family structure influences allergic sensitization, suggesting an environmental effect rather than reporting bias.
- Sibship size and birth order effects support a protective role for postnatal infections.
- The critical period for this protective effect appears to extend beyond the first month of life and first allergen exposure.
Objective:
To determine whether increased numbers of siblings and infection in early life protect against allergic sensitisation.
Design:
Historical cohort study.
Setting:
Sheffield, UK.
Subjects:
11,765 children aged 11-16 years for whom a history of neonatal infectious illness had been recorded systematically at 1 month of age.
Methods:
A history of hay fever and family structure was obtained by postal questionnaire; neonatal illness history was ascertained from health visitor records; 723 children underwent skin prick testing with mixed grass pollen extract.
Results:
The prevalence of hay fever was reduced (p < 0.0001) among children of younger mothers, and those from larger families. The number of older siblings exerted a stronger independent effect than the number of younger siblings (p < 0.001). Infants breast fed exclusively during the first month were at higher risk (p < 0.05) of subsequent hay fever, independent of demographic factors. Adolescents at high risk of hay fever by virtue of their family structure were more likely to be sensitised to grass pollen (p < 0.002). No significant relations emerged between hay fever and infection in the first month of life, even among children born in June.
Conclusions:
The association of hay fever with family structure is not due to reporting bias and reflects an environmental influence on allergic sensitisation. The effects of sibship size, birth order, and infant feeding are consistent with a protective influence of postnatal infection. The first month of life and the first postnatal exposure to allergen are not the critical periods during which this protective effect is determined.