Associations (odds ratio (95% confidence interval)) between risk factors in childhood and asthma by age at onset#
| Age at asthma onset | ||||
| ≤8 years | 9–13 years | 14–19 years | >19 years | |
| Female sex | 0.74 (0.54–0.99) | 0.93 (0.66–1.29) | 1.84 (1.33–2.56) | 1.22 (0.78–1.91) |
| Family history of asthma | 3.30 (2.43–4.48) | 3.25 (2.31–4.57) | 1.55 (1.08–2.24) | 2.04 (1.25–3.34) |
| Low birthweight | 1.87 (1.04–3.36) | 1.24 (0.55–2.78) | 1.15 (0.54–2.44) | 2.12 (0.94–4.82) |
| Breastfeeding <3 months | 2.02 (1.45–2.81) | 0.63 (0.40–0.98) | 1.57 (1.10–2.23) | 1.75 (1.07–2.85) |
| Smoking during pregnancy | 1.30 (0.93–1.84) | 1.54 (1.05–2.25) | 1.33 (0.93–1.90) | 0.78 (0.45–1.35) |
| Any severe respiratory infection | 2.76 (1.95–3.90) | 1.31 (0.93–1.84) | 1.11 (0.80–1.52) | 1.06 (0.68–1.67) |
| Rhinoconjunctivitis | 6.55 (4.47–9.61) | 2.78 (1.68–4.59) | 1.48 (0.80–2.74) | 1.50 (0.61–3.65) |
| Eczema | 1.75 (1.29–2.37) | 1.30 (0.93–1.83) | 1.20 (0.86–1.66) | 0.87 (0.53–1.41) |
| Allergic sensitisation | 3.20 (2.16–4.74) | 2.92 (1.87–4.55) | 2.23 (1.45–3.43) | 1.95 (0.97–3.94) |
#: analysed in a multivariable multinomial regression analysis, with never-asthma as reference.