to the editor: Thank you for this very informative article. It did not specifically discuss the importance of vitamin D supplementation. The American Academy of Pediatrics (AAP) recommends that all infants consume a minimum of 400 IU per day of vitamin D beginning shortly after birth, particularly breastfed or partially breastfed infants.¹ Human breast milk is low in vitamin D, containing less than 25 IU per L.² Even with adequate oral intake, a premature infant would still receive far less than the recommended daily amount of vitamin D.

The article does mention that breast milk can be supplemented with a multinutrient fortifier, but that benefit postdischarge is not clear. Although common commercial preparations, (e.g., Similac Human Milk Fortifier, Enfamil Human Milk Fortifier) contain vitamin D, breastfed infants discharged without fortified milk will not benefit from this type of vitamin D supplementation. Sequelae of vitamin D deficiency among breastfed infants, such as rickets and hypocalcemia, are not common; however, supplementation is essential to prevent potential illness in this already vulnerable patient population.

in reply: We thank Dr. Shipley for the astute observation regarding vitamin D deficiency, osteopenia, and metabolic bone disease in graduates of neonatal intensive care units. Prematurity and the metabolic demands of sick newborns can put them at high risk of poor bone growth and health.¹

Our article focused on guidelines for the outpatient follow-up of newborns discharged from neonatal intensive care units that deviate from routine newborn care and guidelines. As Dr. Shipley stated, the AAP recommends that all infants, shortly after birth, begin receiving 400 IU per day of vitamin D.^2,3 This can be achieved with consumption of greater than 1 L per day of formula (which usually occurs by approximately one month of age) or vitamin D supplementation for those infants consuming breast milk or less than 1 L per day of formula (i.e., mixed feeding). This recommendation does not differ for graduates of neonatal intensive care units.

Regarding fortification of human breast milk, our discussion was to address concerns of extrauterine growth failure, not vitamin deficiencies. If breast milk is to be fortified as an outpatient, it is typically done with formula, as human milk fortifiers are not readily available other than for inpatient use. Because the amount of vitamin D provided would likely be less than 400 IU per day, supplementation is recommended.^2–4

Recently published studies suggest increasing the recommended vitamin D dosage to 800 IU per day. In a randomized double-blind trial (n = 96), the prevalence of vitamin D deficiency was significantly lower in preterm infants receiving 800 IU per day than in those receiving 400 IU per day at 40 weeks (38% vs. 67%) and at three months corrected age (12% vs. 35%). However, there was no improvement in bone mineralization between the two groups. One infant receiving 800 IU per day had vitamin Dexcess.⁵ In 2008, the AAP released new recommendations increasing the dosage of vitamin D from 200 to 400 IU per day based on growing evidence of vitamin D deficiencies in infants receiving lower dosages. Until larger trials are completed, 400 IU per day of vitamin D supplementation is the best evidence-based recommendation.

Interestingly, a longitudinal survey from 2010 revealed that very few infants were receiving adequate vitamin D supplementation. Only 5% to 13% of breastfed infants, 9% to 14% of mixed-fed infants, and 20% to 37% of formula-fed infants met the AAP recommendation.⁶ This evidence underscores the importance of vitamin D supplementation. Clinicians are encouraged to inquire about ingestion of vitamin D in this at-risk population.