A national survey conducted between 2005 and 2007 examined information on babies who had had been breast fed, formula fed or who received mixed feedings.
The study showed that no matter how they were fed only half of infants got the 200 units of Vitamin D recommended.
Researchers say the consequences may not be apparent for many years but they are serious.
There's growing concern that not enough Vitamin D early on may mean an increased risk of cancer or other diseases later in life.
