The Association Between Being Breastfed in Infancy and Risks of Cancer in Adulthood—a UK Biobank Study

Being breastfed has established benefits for infant health, but its long-term effects on adult diseases, including cancer, remain underexplored. We examined associations between being breastfed in infancy and the risks of common cancers. Data from 339,115 participants (191,117 women) enrolled in the UK Biobank with self-reported breastfeeding data were linked to national cancer registries. Cox models estimated sex-specific hazard ratios (HR) and 95% confidence intervals (CI) for the associations between being breastfed (ever/never) and risks of overall cancer as well as common cancer sites. In total, 34,392 incident cancers (17,895 in women) were registered. The HR of overall cancer associated with being breastfed was 1.05 (95% CI 1.01–1.09) in women and 1.00 (95% CI 0.96–1-04) in men. In site-specific analysis being breastfed was associated with an increased risk of breast and ovarian cancer in women and a reduced risk of oesophageal cancer in men. We found that having been breastfed was associated with a marginally increased risk of adult cancer in women, but we found no evidence of an association in men. These findings should be viewed within the study limitations, and do not outweigh the many benefits that breastfeeding provides.