Final answer:
Newborns are given vitamin K at birth to prevent vitamin K deficiency bleeding, as they naturally have low levels due to inadequate transfer via the placenta, a sterile gut with no bacteria to produce the vitamin, and the low vitamin K content in breast milk.
Step-by-step explanation:
A single dose of vitamin K is administered to newborns at birth to prevent a condition called vitamin K deficiency bleeding (VKDB), which can lead to serious bleeding issues in the infant. Newborns have a natural deficiency because vitamin K is not sufficiently transmitted from the mother's placenta before birth and the sterile gut of a newborn does not yet have the bacteria that synthesize the vitamin. Moreover, breast milk contains lower levels of vitamin K. The single dose helps in the absorption of ions by the colon and plays a key role in blood clotting. Without this intervention, the insufficient vitamin K levels in a newborn could lead to hemorrhaging and serious health complications.