To assess the relationship between breastfeeding and the risk of developing nephrotic syndrome using a population-based nationwide birth cohort in Korea.

This nationwide cohort study utilized data from the National Health Information Database and the National Health Screening Program for Infants and Children. The study included all children born between January 1, 2010, and December 31, 2018, who underwent their first health screening, which included a specific questionnaire on breastfeeding between 4 and 6 months of age. Associations between nephrotic syndrome and exclusive breastfeeding were estimated using adjusted hazard ratios (aHR) derived from Cox proportional hazards models, adjusted for sociodemographic variables, with follow-up until the occurrence of nephrotic syndrome, 8 years postindex date, death, or December 31, 2022, whichever was first.

The study population comprised 1 787 774 children (median follow-up: 7.96 years; IQR: 6.31-8.00 years), including 612 556 exclusively breastfed and 1 175 218 formula-fed children. Exclusive breastfeeding was associated with a decreased risk of developing nephrotic syndrome (aHR: 0.80; 95% CI: 0.69-0.93). Subgroup analysis stratified by sex mirrored the overall findings, although statistical significance was not observed in girls (boys: aHR, 0.75; 95% CI, 0.62-0.92; girls: aHR, 0.87; 95% CI, 0.70-1.09). Sensitivity analysis confirmed these results.

Exclusive breastfeeding was associated with a 20% reduced risk of developing nephrotic syndrome up to 8 years of age.