Supplemental Vitamin D is recommended for breastfed infants regularly but it is VERY important to look closely at the label. Your provider will likely recommend 400 IU/day which in the most commonly available product is 1 ml (about 20 drops), but in some newer products which are better formulated (in my opinion) the dose could be 0.25ml or even just one single drop (which is really easy to apply to the nipple while feeding or drip into a bag of pumped milk)!
I’m a big fan of simple and like to avoid unnecessary inactive ingredients (ie. the yellow label, more about this coming soon!!!) so I tend to recommend products with Vitamin D in an oil such as olive, coconut, or MCT oil.
Above you can see example photos of a few different Vitamin D products. Remember always read the label carefully.