Most infants in the US are not getting adequate amounts of vitamin D.  Among those exclusively breast fed, only 5% to 13% met the guidelines for 400 IUs of vitamin D daily.  For those formula fed, only 20% to 37% did.  (Pediatrics, March 2010).  In children, low levels of vitamin D have been associated with asthma, influenza, respiratory infections, growth abnormalities, muscle weakness, osteoporosis, diabetes, and cardiovascular risk factors.  All children should be taking a supplement of 400 IUs of vitamin D3 daily.