© 2016 Roy Benaroch, MD
“Breast is best” is a simple, catchy phrase—but to be honest, it’s one that should be followed by a bunch of asterisks and qualifiers. Some mother-baby pairs have a hard time with nursing, and need support and understanding (rather than a simple dismissal of their concerns.) And breast milk, we know, isn’t a great source of absorbable iron, which is especially an issue for premature babies. But the biggest drawback of human breastmilk, compared with commercial formula, is that it is an inadequate source of vitamin D.
A new study shows that this doesn’t have to be the case. Perhaps insufficient vitamin D isn’t really a fundamental problem with breast milk, but a problem with mom’s vitamin D intake.
Backing up a second – we’ve known for a long time that breast-fed babies are much more at-risk for nutritional rickets than formula-fed babies. This is especially true for families with dark skin. Rickets is caused by insufficient vitamin D, and can lead to poor growth, bowed limbs, and other health problems. For most of human history our vitamin D came from sunlight exposure. The skin of babies and mothers can manufacture vitamin D, though it requires sunlight to do it. Darker skin is less efficient at making vitamin D than lighter skin.
To combat the risk of insufficient vitamin D in breast-fed babies, the AAP has recommended a daily vitamin D supplement, starting from birth. In practice, this recommendation is followed maybe 20% of the time. Parents don’t like to give their newborns medicine, and I think pediatricians are reluctant to focus on the possible inadequacies of human breast milk.
In the current study, researchers sought to determine if giving higher doses of vitamin D to nursing moms could result in enough vitamin transfer in their milk. 334 mother-infant pairs were recruited, and randomized into three groups. In group one, moms were given an ordinary vitamin supplement, and their babies a vitamin D supplement (400 IU/day, matching the current recommendation.) In group 2, the babies were given no extra D, but moms took 2400 IU/day; in group three, moms were given 6400 IU each day. Babies and moms underwent regular blood and urine tests to see if these doses resulted in good vitamin D levels in the babies, and to see if these doses caused any metabolic problems with vitamin D, phosphorus, or calcium metabolism.
There was a relatively high drop-out rate—of the original 334 pairs, just 148 stuck with the plan for exclusive breastfeeding, and were thus able to complete the trial (families who discontinued breastfeeding or added formula supplements were not included in the final analysis.)
All of the babies who received regular supplementation had robust vitamin D levels and normal biochemical testing – we know, if that 400 IU a day for babies is given, it works. That was group 1. Group 2, where moms were given vitamin D 2400 IU/day, was a failure—they actually stopped this arm of the study early, because many of the babies in this group did not have adequate vitamin D levels on their blood tests. But the babies in group 3 – who themselves received no direct vitamin D supplements, but whose moms got 6400 IU/day—did as well as group 1, with perfectly good vitamin D levels and no evidence for any side effects or problems. And, bonus, their moms also benefitted, with normal vitamin D levels and no side effects.
A reasonable question, though—is 6400 IU of D a day safe for moms to take? A prior guideline from the Institute of Medicine had suggested an upper limit of 2000 IU/day (though that has since been increased to 4000); the Endocrine Society now sets their upper limit at 10,000. During the past decade many studies have used adult D supplementation in the range of thousands of units per day, and according to the authors of this paper not a single adverse event was observed.
This study supports a safe alternative for families, and perhaps one that’s easier to do. Moms are used to taking prenatal vitamins, and continuing to take them while nursing. Adding 6,000 IU of D to the typical 400 in a prenatal isn’t expensive, and seems to be safe and effective at making sure their babies get enough D. Breast milk can have enough D – but only if mom gets her own supplement.