Just seen you are doing both :) By rule...babies get all the nutrients they need from formula/breast milk. If on less than the recommended amount of formula aday...they need additional vitamin D/vitamins. But when breast fed...mothers are providing them with vitamin D etc until at least 6 months (at weaning age) So i took supplements throughout pregnancy and breast feeding to insure she was getting enough vitamins. Then at 6 months...my HV told me to give her a multivitamin or vitamin D drops which i do :) X