 Neonates from hospitals in the greater Montreal area will be studied. Neonates will be screened for low vitamin D status within 48 h of birth for 25OHD to enable rapid entry into study groups. Those with serum 25OHD 50 nmolL will be randomized to 400 or 1000 IUd until 1 y of age. Those with 25OHD 50 nmolL will be provided standard of care 400 IUd and form a reference group. 