Breast-feeding influences thymic size in late infancy

We have previously shown that breast-fed infants have a considerably larger thymus at 4 months than formula-fed infants. The aim of the present study was to investigate whether breast-feeding also influences the thymic size i n late infancy. In a cohort of 50 infants, all being partially breast-fed w hen recruited at 8 months, ultrasound assessment of the thymic index (a vol ume estimate) was performed at both 8 and 10 months of age. At 10 months th e thymic index was significantly higher in those still being breast-fed com pared to infants who had stopped breast-feeding between 8 and 10 months of age (P = 0.05). This difference became more significant when controlled for the influence of infectious diseases (P = 0.03). In infants still breast-f ed at 10 months then was a significant correlation between the number of br east-feeds per day and their thymic index (P = 0.01). Conclusion The effect of breast-feeding on thymus size is likely to be caus ed by immune modulating factors in breast milk. Breast milk influences thym ic size in late infancy.