BACKGROUND Impaired fetal growth may be a risk factor for asthma although evidence in children is conflicting and there are few data in adults. Little is known about risk factors which may influence asthma in late childhood or early adult life. Whilst there are clues that fatness may be important, this has been little studied in young adults. The relations between birth weight and childhood and adult anthropometry and asthma, wheeze, hayfever, and eczema were investigated in a nationally representative sample of young British adults.

RESULTS The prevalence of asthma at 26 years fell with increasing birth weight. After controlling for potential confounding factors, the odds ratio comparing the lowest birth weight group (<2 kg) with the modal group (3–3.5 kg) was 1.99 (95% CI 0.96 to 4.12). The prevalence of asthma increased with increasing adult BMI. After controlling for birth weight and other confounders, the odds ratio comparing highest with lowest quintile was 1.72 (95% CI 1.29 to 2.29). The association between fatness and asthma was stronger in women; odds ratios comparing overweight women (BMI 25–29.99) and obese women (BMI ⩾30) with those of normal weight (BMI <25) were 1.51 (95% CI 1.11 to 2.06) and 1.84 (95% CI 1.19 to 2.84), respectively. The BMI at 10 years was not related to adult asthma. Similar associations with birth weight and adult BMI were present for wheeze but not for hayfever or eczema.

CONCLUSIONS Impaired fetal growth and adult fatness are risk factors for adult asthma.