It depends on what he’s drinking.
Although some vitamin D does pass from mother to child in breast milk, it’s hard to know just how much since it can vary from mother to mother. So the American Academy of Pediatrics recommends that all breastfed babies receive 400 IU of liquid vitamin D a day until they’re weaned or they’re drinking 32 ounces a day of vitamin D-fortified formula. (There is one well-known authority that disagrees with the AAP’s recommendation. La Leche League says that breast milk contains everything a baby needs, and that the risk of rickets is very low.)
Even if your baby is formula-fed, the AAP also suggests supplementing with 400 IU of vitamin D a day until he’s drinking at least 32 ounces a day of fortified formula.
Why is it so important? The body uses vitamin D to help absorb calcium and other nutrients. So the real risk of a deficiency is rickets, a bone-softening disease that causes symptoms like bowed legs, soft skulls, and delays in crawling and walking.
Even past the first six months, kids may be at a higher risk for deficiency if they live in high latitudes or in places with poor air quality or dense cloud cover or if they have dark skin. If in doubt, ask your physician. And of course, be sure to use a natural broad spectrum sunscreen on older babies and kids, like California Baby SPF 30 Sunscreen.