Table 1

Characteristics of subjects included in the study

BMI quintile 1BMI quintile 2BMI quintile 3BMI quintile 4BMI quintile 5p value for trend
*Atopy was defined as a positive reaction of ⩾3 mm to any of a panel of eight common aeroallergens.
**Either mother or father.
Total no
    Boys584630619611563
    Girls589595569598625
Mean (95% CI) BMI
    Boys14.6 (14.5 to 14.7)15.8 (15.8 to 15.8)16.7 (16.6 to 16.7)18.0 (17.9 to 18.1)21.7 (21.4 to 21.9)<0.001
    Girls14.5 (14.4 to 14.6)15.9 (15.9 to 16.0)17.2 (17.1 to 17.2)18.9 (18.8 to 18.9)22.3 (22.1 to 22.5)<0.001
Mean (95% CI) height (cm)
    Boys136.7 (136.1 to 137.2)136.3 (135.7 to 136.8)137.4 (136.9 to 138.0)138.4 (137.9 to 139.0)140.7 (140.0 to 141.3)<0.001
    Girls135.6 (135.0 to 136.2)135.8 (135.2 to 136.5)137.1 (136.5 to 137.7)139.0 (138.4 to 139.6)140.3 (139.6 to 140.9)<0.001
Mean (95% CI) age (years)
    Boys9.95 (9.88 to 10.03)9.68 (9.61 to 9.76)9.71 (9.63 to 9.79)9.77 (9.70 to 9.84)9.81 (9.73 to 9.88)<0.001
    Girls9.80 (9.73 to 9.88)9.68 (9.60 to 9.75)9.77 (9.70 to 9.84)9.83 (9.76 to 9.91)9.70 (9.62 to 9.77)0.01
Mean (95% CI) prevalence of atopy* (%)
    Boys48.2 (44.2 to 52.3)41.8 (38.0 to 45.7)44.4 (40.5 to 48.3)43.9 (40.0 to 47.8)45.2 (41.1 to 49.3)0.56
    Girls31.4 (27.7 to 35.2)33.7 (29.9 to 37.5)33.1 (29.2 to 37.0)37.3 (33.5 to 41.1)38.5 (34.7 to 42.3)0.004
Mean (95% CI) prevalence of family history of asthma** (%)
    Boys24.9 (21.4 to 28.4)29.8 (26.2 to 33.4)30.3 (26.7 to 33.9)25.9 (22.4 to 29.4)28.9 (25.2 to 32.6)0.52
    Girls27.0 (23.4 to 30.6)25.8 (22.3 to 29.3)27.7 (24.0 to 31.4)29.7 (26.0 to 33.4)28.1 (24.6 to 31.6)0.29
Mean (95% CI) prevalence of smoker in family** (%)
    Boys29.9 (26.2 to 33.6)31.8 (28.2 to 35.4)31.0 (27.4 to 34.6)34.4 (30.6 to 38.2)39.7 (35.7 to 43.7)<0.001
    Girls32.4 (28.6 to 36.2)33.2 (29.4 to 37.0)33.1 (29.2 to 37.0)34.3 (30.5 to 38.1)42.7 (38.8 to 46.6)<0.001