In short – yes.
Vitamin D is a fat-soluble vitamin that helps our bodies to absorb calcium and build healthy bones and teeth. Our bodies make vitamin D in the skin when it is exposed to UV-B light. Babies begin to store vitamin D before they are born as it is transferred from their moms through the placenta. Moms with low vitamin D levels are more likely to have babies with low levels as well. Vitamin D deficiency can result in rickets (softening or weakening of the bones) and low calcium levels. Other risk factors for low vitamin D include darker skin, living at higher latitudes, and the winter season (no sunshine!). Babies seem to hit their lowest levels between 3 and 6 months.
Although breast milk provides such good nutrition for babies, it does not contain enough vitamin D in it to help babies reach normal levels- even if mom is taking recommended or higher doses of the vitamin. Thus, we recommend breastfed babies receive vitamin D supplementation of 400 IU/day by mouth. Many formulations are available, most of which are 400 IU/mL – so it’s a small amount, given by a dropper.
Commercially prepared formulas typically have about 400 IU vitamin D per liter of formula – that’s about 34 ounces per day. So, if you are supplementing your breastfeeding with formula, or your baby takes less than 34 oz total in 24 hours, then it’s also recommended to supplement.