Sodium content was analysed in the expressed breast milk from 30 mothe
rs. Measurements were taken up to 24 days postpartum, during which tim
e the mothers expressed manually or by means of a pump. Statistical an
alysis has confirmed not only the known decline in sodium levels postp
artum but has also shown a significantly higher sodium content in manu
ally expressed milk compared to that from pump expressed milk. This fi
nding suggests that the method of expression may alter the sodium conc
entration in human breast milk, thus potentially reducing the amount o
f sodium supplementation required by some preterm infants.