Associations between breastfeeding duration and respiratory tract infections
| Breastfeeding duration as categorical exposure | Unadjusted (n=4040) | Adjusted# (n=3963) | ||
| OR (95% CI) | p-value | OR (95% CI) | p-value | |
| Frequent colds | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| ≤6 months | 0.97 (0.82–1.16) | 0.749 | 1.00 (0.83–1.21) | 0.985 |
| >6 months | 0.99 (0.80–1.24) | 0.958 | 1.01 (0.80–1.27) | 0.953 |
| Ear infections | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| ≤6 months | 0.91 (0.80–1.05) | 0.198 | 0.97 (0.84–1.13) | 0.710 |
| >6 months | 0.84 (0.70–0.99) | 0.048 | 0.88 (0.73–1.06) | 0.177 |
| Croup | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| ≤6 months | 0.92 (0.71–1.19) | 0.523 | 0.95 (0.72–1.26) | 0.738 |
| >6 months | 0.92 (0.66–1.28) | 0.612 | 0.86 (0.60–1.23) | 0.408 |
| Bronchiolitis | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| ≤6 months | 0.79 (0.64–0.97) | 0.028 | 0.89 (0.70–1.12) | 0.316 |
| >6 months | 0.68 (0.51–0.91) | 0.009 | 0.72 (0.52–0.97) | 0.034 |
| Pneumonia | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| ≤6 months | 1.28 (0.70–2.35) | 0.421 | 1.44 (0.76–2.73) | 0.260 |
| >6 months | 1.18 (0.55–2.55) | 0.675 | 1.11 (0.48–2.55) | 0.810 |
| Breastfeeding duration as continuous exposure | Unadjusted (n=2286) | Adjusted# (n=2248) | ||
| OR¶ (95% CI) | p-value | OR¶ (95% CI) | p-value | |
| Frequent colds | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| Breastfeeding (per month) | 1.00 (0.98–1.03) | 0.736 | 1.00 (0.98–1.03) | 0.734 |
| Ear infections | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| Breastfeeding (per month) | 0.99 (0.97–1.01) | 0.277 | 0.99 (0.97–1.01) | 0.408 |
| Croup | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| Breastfeeding (per month) | 1.00 (0.96–1.04) | 0.827 | 0.99 (0.95–1.03) | 0.571 |
| Bronchiolitis | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| Breastfeeding (per month) | 0.95 (0.91–0.99) | 0.016 | 0.96 (0.92–1.00) | 0.054 |
| Pneumonia | ||||
| No breastfeeding | 1.00 | 1.00 | ||
| Breastfeeding (per month) | 1.00 (0.91–1.10) | 0.972 | 1.00 (0.90–1.11) | 0.991 |
Baseline group: children that had never been breastfed. #: for sex, ethnicity, socioeconomic status (Townsend deprivation score), perinatal factors (gestational age, birthweight, birth season), environmental factors (pre- and post-natal maternal smoking, number of older siblings, day care attendance) and family history of asthma, hay fever and bronchitis. ¶: ORs here are presented as odds with every 1-month increase of breastfeeding duration compared to odds of children who had never been breastfed.