Prolonged Breastfeeding at 18 Months and Early Childhood Caries at Age 3 Years: A Population‐Based Cohort Study From Japan

BACKGROUND: Breastfeeding is recommended to 2 years or beyond, but its association with early childhood caries (ECC) after infancy remains uncertain, partly because of inconsistent adjustment for confounders and reverse causation. AIM: To examine whether breastfeeding at 18 months was associated with dental caries at age 3 years. DESIGN: Japanese check-up cohort (2014-2019). Logistic regression estimated odds ratios (ORs), adjusting for sex, regular sweetened juice consumption, screen time > 1 h/day, parental tooth-brushing assistance, single-parent household and parental employment; sensitivity analyses adjusted for or excluded those with 18-month caries. RESULTS: Of 69 165 children, 12 788 (18.5%) were breastfeeding at 18 months. Any caries (35.9% vs. 23.7%) and severe caries (19.2% vs. 10.5%) were more common in breastfeeding children. After behavioural and socioeconomic adjustment, breastfeeding remained associated with any caries (OR 1.89, 95% CI 1.82-1.98) and severe caries (OR 2.14, 95% CI 2.03-2.26); associations persisted after adjustment for caries at 18 months (any caries OR 1.74; severe caries OR 1.87). CONCLUSION: Breastfeeding at 18 months was independently associated with higher odds of ECC at 3 years; reverse causation alone did not account for this. Findings support integrating targeted oral-health counselling, including avoidance of feed-to-sleep and post-feed oral cleaning, into breastfeeding support after infancy.