Obviously I'll need to ask the doctor. However since it's Friday and I'm curious I'd love to hear what you ladies are doing. I am BFing 1/2 the time and supplementing the other half. Should I still give him his vitamin D drop or is he getting enough from the formula and the bit of sunlight he takes in?

BFP # 1 - June 2nd, 2011 - EDD Feb 5, 2012 Birthday Feb 10, 2012
BFP # 2 - Jan 19, 2012 - EDD Sept 24, 2013 - CP Jan 24, 2012
Re: Vitamin D and Supplementing
In addition to being absolutely necessary to prevent rickets a bone weakness disease, low Vitamin D levels are being studied for links to a wide range of immune system issues and GI disorders. The 400 IU reccomended dose in America is actually quite low, when compared to European countries. And in Canada, they actually recommend an 800 IU dose for babies in the winter, due to relative lack of high intensity sun exposure.
Vitamin D is necessary to your babies health, and it is super easy to give them the right dose. Carlson's D drops on Amazon are the best. Just one drop gives a full day's dose, and one bottle lasts an entire year. No artifical flavors or sweeteners or anything except Vitamin D suspended in coconut oil.
Melodic Insomniac
I BF and have never supplemented. I don't give DD any vitamins other than what she gets in the BM. She's fine. My friends do this too and for some reason NONE of them had even heard of giving a vitamin supplement to a BF baby from their pedi... and yes they go to totally "normal" pedis. Flame away, but unless I am shown with bloodwork that DD truly needs vitamins that she's not getting from BM then I won't be adding them in. It's just not necessary.
ETA- I have given them to her 2 times total, many months ago. Once by mouth- bad experience since I don't have the 1 drop kind, and once in a bottle of BM (looked NASTY). Maybe if I had the 1 drop kind it wouldn't be so bad, but I still don't think they are necessary.
Have you done a bone scan on your daughter to assess her bone strength? Can you see her tooth buds under her gums to see if her teeth are developing at the maximum possible density? Do you know kiddos that have developed the horrible disease rickets because their moms naively thought that their BM was enough? My husband treats those kids, whose bones and teeth will suffer permanent damage from their parents' uneducated decisions.
But, hey, if it is too much trouble for you to give your daughter one drop of vitamin a day, I guess that is just tough luck for your LO...
Sorry so harsh, but why are we so hyperconcerned about the exact ounces our LOs drink, the types of food they eat, and try to give them every development edge possible, but people are so super comfortable completely disregarding their physician's recommendation to give their LOs a necessary vitamin?
Society has changed. We now now not to leave our babies out in the sun all day because sunburns are bad and lead to cancer later in life. But the trade off to not as much sun exposure, and we are talking hours, not minutes of being in the sun, is that we need to supplement vitamin D. There are literally zero drawbacks to supplementing, and so many advantages. Please bear the inconvenience of supplementing for your baby's sake.
I wouldn't be too concerned if I were you unless your baby is never in the sun. However extra vitamin D won't hurt so if you're at all concerned you may as well give the supplement.