Vitamin D is needed to support healthy bone development and to prevent rickets, a condition that causes weak or deformed bones. Vitamin D deficiency rickets among breastfed infants is rare, but it can occur if an infant does not receive additional vitamin D from foods, a vitamin D supplement, or adequate exposure to sunlight.
Breast milk alone does not provide infants with an adequate amount of vitamin D. Shortly after birth, most infants will need an additional source of vitamin D.
To avoid developing a vitamin D deficiency, the Dietary Guidelines for Americans and American Academy of Pediatrics recommend breastfed and partially breastfed infants be supplemented with 400 IU per day of vitamin D beginning in the first few days of life. Families who do not wish to provide a supplement directly to their infant should discuss with a healthcare provider the risks and benefits of maternal high dose supplementation options.
Once a child has started eating solid foods, parents can make sure their child is getting enough vitamin D from foods or supplements.
Why are infants at risk for vitamin D deficiency?
The risk for vitamin D deficiency is increased when there is limited exposure to sunlight or when an infant is not consuming an adequate amount of vitamin D. Although reducing sun exposure is important for preventing cancer, it also decreases the amount of vitamin D that a person can make from sunlight.
Other factors that decrease the amount of vitamin D a person can make from sunlight include:
Original reference: https://www.cdc.gov/breastfeeding/breastfeeding-special-circumstances/diet-and-micronutrients/vitamin-d.html#print