Does oral maternal Vitamin D supplementation normalize the Vitamin D level in exclusively breastfed infants?

Summary of the Issues:

Adequate vitamin D is essential for proper bone development and prevention of skeletal abnormalities.¹ Neonatal vitamin D deficiency is associated with rickets, altered calcium metabolism, poor growth, early childhood tooth decay, asthma, and an increased risk of diabetes.² Lower vitamin D levels have also recently been linked to an increased risk of acute lower respiratory tract infections including respiratory syncytial virus.³ It has been long accepted that breast milk is the ideal source of nutrition for infants, however, data reveals that on average, breast milk contains <20% of the daily recommended dose of vitamin D.⁴ The actual normal laboratory value corresponding to adequate vitamin D is controversial; therefore, for this review, the lower limit of normal is considered to be a 25 (OH)D level of 20 ng/mL.

Vitamin D deficiency is common, but does vary according to geographical location and race. For example, the risk of deficiency is elevated in areas of higher latitude and during the winter months since vitamin D is synthesized when the skin is exposed to sunlight.¹ The American Academy of Family Physicians recommends 400 IU/day of oral vitamin D for all exclusively breastfed infants regardless of race or location.⁵ However, daily supplementation may be cumbersome and compliance with this recommendation is suboptimal. It has been hypothesized that breastfeeding mothers may take an oral vitamin D supplement and supply the recommended dose to their infant solely through their breast milk. This brief review analyzes whether parents may forego infant supplementation and simply utilize oral maternal supplementation to provide their child with an adequate vitamin D supply.

Summary of the Evidence:

A detailed literature review revealed multiple studies addressing vitamin D levels in exclusively breastfed infants. A 2017 Japanese longitudinal study found that 97% of 38 term, healthy, exclusively breastfed infants were vitamin D deficient with 25 (OH)D levels < 20 ng/mL at birth and all were deficient at 5 months of life.¹ Another study in 2003 found that 82% of the infants studied were not only vitamin D deficient, but had levels < 10 ng/mL.³ In a 2014 Brazilian study, it was discovered that vitamin D levels of mothers were deficient in 85% of cases, while 80.5% of their neonates were deficient as well.⁶ This evidence is of paramount importance since exclusively breastfed babies have a higher risk of hypokalemic seizures and rickets in comparison to formula-fed infants.¹ Evidence clearly indicates that neonatal vitamin D deficiency is a widespread issue.

A potential simple solution for this common issue is to determine whether maternal supplementation of vitamin D is sufficient in providing the recommended amount through breast milk for exclusively breastfed infants. Wagner, et al’s randomized, controlled pilot trial found that supplementing breastfeeding mothers with a high dose of 6,400 IU/day of oral vitamin D in comparison to oral supplementation of newborns with 400 IU/day were equivalent.⁷ A similar and more recent randomized, double-blind, comparative effectiveness trial studied maternal dosing of 6,400 IU/day of vitamin D with 400 IU/day for the mother plus 400 IU/day for the infant. This study also found that 6,400 IU/day “safely and significantly increased maternal vitamin D,” and most importantly infants receiving traditional oral 400 IU/day did not differ from those whose mothers alone were receiving 6,400 IU/day.⁸

The efficacy of maternal supplementation has therefore been confirmed, yet the optimal dose has yet to be established. The optimal dose is difficult to determine as the recommended normal serum value of vitamin D remains controversial. March et al’s double-blind randomized controlled study classified adequate vitamin D levels as > 12 ng/mL instead of 20 ng/mL.² They supplemented mothers during gestation and continued at least eight weeks postpartum. They reported that 400 IU/day, 1,000 IU/day, and 2,000 IU/day normalized vitamin D levels in 57%, 84%, and 98% of infants, respectively. Basile, et al set a higher goal for normal vitamin D at > 32 ng/mL and discovered maternally supplemented doses of 2,000-4,000 IU/day were effective in achieving normal vitamin D levels in all infants. This 2006 study indicated that although the 2,000 IU/day dose was adequate, the 4,000 IU/day regimen was more effective in raising both maternal and infant serum levels.⁹ Furthermore, a 2013 randomized, controlled trial by Oberhelman, et al compared an oral dose of 5,000 IU/day with a single high dose of 150,000 IU vitamin D. The study followed 40 mothers and infants and discovered that both doses resulted in normal infant vitamin D levels of > 20 ng/mL.¹⁰

Comments:

Evidence clearly suggests that maternal vitamin D supplementation alone in doses >2,000 IU/day is appropriate for providing adequate vitamin D to most exclusively breastfed infants. Further studies are needed to finalize the accepted normal vitamin D value as well as the recommended dose for maternal supplementation.

Clinical Question:

Does oral maternal Vitamin D supplementation normalize the Vitamin D level in exclusively breastfed infants?

Answer:

Yes. Based on multiple randomized, controlled studies, oral maternal supplementation of >2,000 IU/day is sufficient to produce adequate vitamin D levels in most exclusively breastfed infants.

Level of Evidence for the Answer:

A