Hay fever, asthma and number of older siblings--a twin study

Clin Exp Allergy. 1997 May;27(5):515-8.


Background: It has been suggested that allergic sensitization is inversely related to the number of siblings in the family.

Objectives: To study whether a similar relation can be observed for hay fever and asthma among Finnish adolescents in a population with relatively low prevalence of atopic diseases.

Methods: A questionnaire mailed to a nationwide sample of 1849 families with 16-year-old twins assessing the cumulative incidence of doctor-diagnosed hay fever and asthma among the adolescents and the number of older siblings in the family by parental report.

Results: The cumulative incidence of hay fever was significantly lower among the adolescents with three or more older siblings (3.9%, 95% CI = 1.2-6.5%) compared with adolescents with fewer older siblings (12.7%, 95% CI = 11.4-14.0%). There was no difference in the cumulative incidence of asthma among the adolescents according to the number of older siblings in the family.

Conclusions: Large number of older siblings appears to be protective against the development of hay fever.

Publication types

  • Research Support, Non-U.S. Gov't
  • Twin Study

MeSH terms

  • Adolescent
  • Asthma / epidemiology*
  • Finland / epidemiology
  • Humans
  • Incidence
  • Rhinitis, Allergic, Seasonal / epidemiology*
  • Sibling Relations*
  • Surveys and Questionnaires