Three myths surrounding vitamin D supplementation in infants are: (1) rickets is rare; (2) children receive enough sunlight; and (3) breast milk contains enough vitamin D from the mother to supply the infant adequately.7 Rickets is no longer rare and poses a threat to infants. The AAP advises against direct sunlight for infants and recommends the use of sunscreen after age 6 months to block UV rays from penetrating the skin. As a result, infants are not receiving sufficient sun exposure to produce enough vitamin D on their own. Breast milk does not contain an acceptable amount of vitamin D; it averages 22 IU/L in vitamin D-sufficient mothers—significantly less than fortification requirements.3-5,8
Vitamin D deficiency
Severe vitamin D deficiency can present as hypocalcemia with tetany or seizures. In periods of active growth, especially infancy and adolescence, hypocalcemia may be the first sign of deficiency caused by the body’s inability to meet the demand for calcium without proper levels of vitamin D to aid in absorption.4,6
Most often, however, vitamin D deficiency presents as osteomalacia, with rickets being osteomalacia of the immature bones. Rickets causes abnormal reorganization of cartilaginous growth. After being vitamin D-deficient for a few months, children with rickets usually present with skeletal deformities, including the classic presentation of genu varum (bowlegs) or genu valgum (knock knees), widening of the wrists and ankles, prominence of the costochondral junctions, and/or skull deformities. Delayed tooth eruption and poor enamel may also be seen, along with an increased number of dental caries.
Although infants who are breastfed are the most susceptible to vitamin D deficiency, breastfeeding is not the only risk factor. Mixed feedings of formula and breast milk as well as formula-only feeding with volumes of less than 1 L/day are also considered risky.7 Other factors that may lead some babies to an an even higher risk for deficiency are prenatal conditions, geographic location, phenotype, and social and economic environment.
Prenatal. All women are advised to take prenatal vitamins throughout pregnancy, yet research suggests that although prenatal vitamins are important, more than 30% of women who take them regularly in the second and third trimester are still vitamin D-deficient.9 One study found that it took vitamin D doses greater than 1,000 IU to achieve 25(OH)D concentrations >50 nmol/L in pregnant women (most prenatal vitamins offer a concentration of 400 IU).6
In utero, it is generally thought that the newborn is able to obtain sufficient stores of vitamin D by robbing the mother. No skeletal malformations or deformities have been seen in neonates of deficient mothers. However, the strongest modifiable risk factor for infant deficiency after birth was maternal deficiency during pregnancy.6,10 If a mother can be kept vitamin D-sufficient during pregnancy, her child is more likely to be sufficient after birth as well.9
Geographic locations. Northern locations are notorious for vitamin D deficiency, especially during the winter months.5 Vitamin D is created when UVB photons penetrate the skin and cause a reaction that turns vitamin D into its active metabolite. The only times UVB rays are concentrated enough and bent correctly to reach the earth’s surface are between 10 am and 3 pm during the spring, summer, and fall. At northern latitudes, the UVB rays filter into the atmosphere at an even more deflected angle than elsewhere, making them even less likely to penetrate the skin.4 Mothers who live in northern locations have breast milk with vitamin D levels that range from 10 to 30 IU/L, which is insufficient to meet the infant’s needs.2
Phenotype. Infants with dark pigmentation are also at an increased risk for vitamin D deficiency because of their skin’s natural solar-reflective qualities. These children require more sun exposure to synthesize large enough amounts of vitamin D in comparison with fair-skinned children. The risk is greater still if the mother has darker pigmentation and is at risk for deficiency herself.8