Influence of smoking on asthmatic symptoms and allergen sensitisation in early childhood.

BACKGROUND

Apart from heredity, several early life environmental factors are implicated in the development of childhood asthma. Maternal smoking is believed to increase asthmatic symptoms but its influence on the development of allergen sensitisation is debatable.

STUDY DESIGN

A whole population birth cohort was reviewed at ages 1, 2, and 4 years. Of 1218 children seen at 4 years, 981 (80.5%) were skin prick tested with a battery of common food and aeroallergens. Smoking history was recorded at birth and updated at each follow up and its impact on the development of asthma and allergen sensitisation in the children was assessed.

RESULTS

Two hundred and fifty mothers smoked during pregnancy (20.5%) and 307 (25.2%) after childbirth. Maternal smoking in pregnancy was associated with low birth weight (mean (SD): 3.3 (0.5) v. 3.5 (0.5) kg; p<0.001). Smoking mothers were more often from lower social classes (31.8% v. 16%, p<0. 001) and they breast fed their babies for a shorter duration (8.5 (11.4) v. 16.6 (15.2) weeks; p<0.001). The difference in breast feeding duration was partly due to a higher proportion of smoking mothers who never breast fed their babies. Although at age 2 years asthmatic symptoms were associated with exposure to maternal tobacco smoke (odds ratio 2.2, 95% confidence interval 1.5 to 3.4; p<0.001), this association was lost by 4 years. However, maternal smoking was a significant risk factor in a subgroup of children with asthmatic symptoms but negative skin prick test. Maternal smoking did not increase allergen sensitisation at age 4 years. No effect of paternal smoking on asthma was observed in the children.