My opinion - Vitamin D supplementation is the newest medical fad. Your daughter only needs 10-15 minutes of sunlight on her hands and face daily to produce the VitD she needs naturally. This exposure to sunlight is not going to give her cancer. We need to remember that most everything is okay in moderation. Please don't buy into the idea that breastmilk is missing something your daughter needs. This is a common medical misconception that has *no basis* in medical fact. The medical community - with it's emphasis on measuring and quantifying everything - simply CANNOT accept that breastmilk is perfect as is, and there is NO BENEFIT to formula feeding over breastfeeding. Breastmilk has been designed as nature's perfect food. Formula has not. Don't buy into the idea that breastmilk is missing something and you need to supplement your daughter. If you are concerned about Vitamin D, you might try supplementing yourself with some fermented cod liver oil. You can buy it in capsules, and it is far and away the best way to get Vit D. I have taken the Green Pastures brand before - you order it online.
If you are concerned about vitamin supplementation, please choose a high-quality, food-based vitamin, or you will simply be wasting your time and money. Most commercial vitamins are basically useless to our bodies. In trying to spend the least amount to produce their vitamin, vitamin companies use forms of the vitamin that are inaccessible to our bodies. That is why we get "vitamin pee" - that nasty smelling, bright colored pee. It is all the insoluble vitamins passing through our systems and down the toilet. If you want to get the benefits of vitamin supplementation, you need to take a good quality, *food based* vitamin. If you take a good vitamin, you will have good nutrients in your breastmilk for your baby. I particularly like the New Chapter Organics. They are 100% food based, and I can tell a difference in my energy level when I haven't taken them for a while. There are other good brands out there, but just make sure it is a food-based vitamin for the best absorption.
In the meantime, I would say to just enjoy your baby and make sure she gets a little sunshine every day. We mothers are way too scared about every little thing that comes down the pike. A few minutes of sunshine is *not* going to give your daughter cancer. An exclusive diet of breastmilk is *not* going to give her rickets.
Best of luck,
S. L