Why are you giving him supplement? What do they feel he needs? Why don't you increase YOUR intake of these vitamins and then he will get them thru your milk? Make sure you are taking a REAL vitamin- one with much higher then a 10% absorbtion rate! Talk to your local Health food store, and check out www.oligofructosecomplex.net for info on absorbtion. I can feel the difference with the oligo- so I KNOW my body is getting it- thus passing it on to my son.
Update to my answer: Many of North americans are deficient in MANY vitamins and unfortunately commercial 'one a days' have fooled many into thinking that they are doing something good, when really they should are just throwing away $. Money that could be buying them better food, or better vitamins. My Dr also recommended Vit D, not because she had checked my levels or the babys levels- but because it is just 'standard'. Well my life isn't standard and she had no way of knowing that I take 2 Tbsp of cod liver oil each morning, and I also make sure my children get sunlight each day. (well, that there is sun) As well as make sure I am taking the best suppliment on the market to ensure that my child is getting what he needs. So if a mother isn't doing all of this- then yes, I agree she may need to suppliment her childs Vit. D and then find a good way to make him take it. I was simply sharing my way of supplimenting my childrens Vit. D. :)