THE ASSOCIATION OF FAMILY-SIZE WITH ATOPY AND ATOPIC DISEASE

Background Studies in children have shown that family size is negative ly associated with atopy and atopic disease. Objective To describe the association of family size with atopy and atopic disease in young adu lts. Methods A randomly selected sample of 1159 men and women aged 20- 44 years provided information on respiratory symptoms, hay fever and e czema. Blood samples were taken for assessment of total IgE and specif ic IgE to house dust mite, grass, cat, Cladosporium and birch. The ass ociation of family size and birth order with respiratory symptoms, ato py and total IgE was assessed by multiple logistic and linear regressi on. Results There was a negative association between family size and t he reporting of 'wheeze with breathlessness' (adjusted odds ratio for an increase of one sibling 0.85; 95% confidence interval 0.75-0.98), ' wheeze without a cold' (adjusted odds ratio for an increase of one sib ling 0.85; 95% confidence interval 0.75-0.98) and 'asthma attacks' in the last 12 months (adjusted odds ratio for an increase of one sibling 0.77; 95% confidence interval 0.61-0.97), current 'hayfever and nasal allergies' (adjusted odds ratio for an increase of one sibling 0.84 9 5% confidence interval 0.75-0.94) and sensitization to grass (adjusted odds ratio for an increase of one sibling 0.87; 95% confidence interv al 0.76-0.99). Birth order was negatively associated with 'hayfever an d nasal allergies' only. A. decreased risk of sensitization to grass i n those from large families did not fully explain the negative associa tion between family size and hayfever. No statistically significant (P > 0.05) association of family size or birth order With the reporting of other respiratory symptoms, eczema, sensitization to the other alle rgens or total IgE was observed. Conclusion There is a negative associ ation between family size and some symptoms suggestive of asthma, 'hay fever and nasal allergies' and sensitization to grass in young adults. There is no consistent, significant association between family size a nd eczema, total ISE or sensitization to other allergens.