BackgroundChildhood-onset asthma (COA) has become a major and growing problem worldwide and imposes a heavy socioeconomic burden on individuals and families; therefore, understanding the influence of early-life experiences such as breastfeeding on COA is of great importance for early prevention.ObjectivesTo investigate the impact of breastfeeding on asthma in children under 12 years of age and explore its role at two different stages of age in the UK Biobank cohort.MethodsA total of 7,157 COA cases and 158,253 controls were obtained, with information regarding breastfeeding, COA, and other important variables available through questionnaires. The relationship between breastfeeding and COA were examined with the logistic regression while adjusting for available covariates. In addition, a sibling analysis was performed on 398 pairs of siblings to explain unmeasured family factors, and a genetic risk score analysis was performed to control for genetic confounding impact. Finally, a power evaluation was conducted in the sibling data.ResultsIn the full cohort, it was identified that breastfeeding had a protective effect on COA (the adjusted odds ratio (OR)=0.875, 95% confidence intervals (CIs): 0.831~0.922; P=5.75×10-7). The impact was slightly pronounced in children aged 6-12 years (OR=0.852, 95%CIs: 0.794~0.914, P=7.41×10-6) compared to those aged under six years (OR=0.904, 95%CIs: 0.837~0.975, P=9.39×10-3), although such difference was not substantial (P=0.266). However, in the sibling cohort these protective effects were no longer significant largely due to inadequate samples as it was demonstrated that the power was only 23.8% for all children in the sibling cohort under our current setting. The protective effect of breastfeeding on COA was nearly unchanged after incorporating the genetic risk score into both the full and sibling cohorts.ConclusionsOur study offered supportive evidence for the protective effect of breastfeeding against asthma in children less than 12 years of age; however, sibling studies with larger samples were warranted to further validate the robustness our results against unmeasured family confounders. Our findings had the potential to encourage mothers to initiate and prolong breastfeeding.

Background To explore the long-term relation between smoking during pregnancy and early childhood growth in the UK Biobank cohort. Methods To estimate the effect of smoking during pregnancy on offspring height and body size at ten years old, we performed a cross-population comparison to examine whether such influence could be repeatedly observed among three different ethnic groups in the UK Biobank cohort (n = 22,140 for European, n = 7,094 for South Asian, and n = 5,000 for African). Especially, we applied the UK Biobank European sibling cohort (n = 9,953 for height and n = 7,239 for body size) to control for unmeasured familial confounders and incorporated a polygenic risk score to adjust for potential genetic effect. Results We discovered that children whose mothers smoked during pregnancy had greater risk of being shorter or fatter at age ten in the full UK Biobank European cohort, with 15.3% (95% confidence intervals (CIs): 13.0 ~ 17.7%) higher risk for height and 32.4% (95%CIs: 29.5 ~ 35.4%) larger risk for body size. Similar associations were identified in the South Asian and African populations. These associations were robust and remained significant in the European sibling cohort (12.6% [95%CIs: 5.0 ~ 20.3%] for height and 36.1% [95%CIs: 26.3 ~ 45.9%] for body size) after controlling for family factors or genetic influence. Conclusion Smoking during pregnancy can promote offspring's height defect and obesity in childhood.