In medical school, I was amazed to learn that 95% of human breast milk contains little or no vitamin D. I thought, “Were paleolithic women supposed to put their newborns in a field to get sun exposure, where they would be easy prey?” It simply struck me as incongruent that nature’s perfect food contains little or no vitamin D.
In March of 2013, Doctor Doria Thiele and colleagues did a systematic review of the literature on the amount of vitamin D a lactating woman needs to maintain adequate vitamin D levels in infants.
They only found three studies that directly addressed the question, two of them by Professors Bruce Hollis and Carole Wagner. They found another study that showed neither 2,000 IU/day nor 60,000 IU/month were adequate to maintain the vitamin D levels in suckling infants. They concluded:
“There is support to conclude that when maternal vitamin D intake is sufficient, vitamin D transfer via breast milk is adequate to meet infant needs. In the reviewed studies, doses up to 10 times the current recommended daily intake of vitamin D were needed to produce sufficient transfer from mother to breastfed infant.”
It was Bruce Hollis and Carole Wagner who first discovered why human breast milk contains little or no vitamin D. It is because almost all modern women are vitamin D deficient. They discovered that lactating women have lots of vitamin D in their breast milk as long as they take 4,000 to 6,000 IU/day of vitamin D/day. They found that breastfeeding women taking only 2,000 IU/day had some vitamin D in their breast milk, but 2,000 IU/day was not enough to sustain adequate vitamin D levels in their infants.
As natural sun exposure in hunter gatherers in Tanzania raise 25(OH)D levels to levels comparable to women taking 6,000 IU/day, it is logical to assume that free living hunter gatherer lactating women have vitamin D in their breast milk. However, to my knowledge, that has never been studied.
So, it looks as if nature did not make a mistake; humans did. It appears that nature always intended human breast milk to have vitamin D. In other words, before the modern age, lactating women must have had lots of vitamin D in their breast milk from sun exposure. To me, the best biomarker for adequate vitamin D levels is simple. What 25(OH)D levels are required for adequate production of vitamin D in breast milk? I have written about this before.
So if you know any breastfeeding moms, tell them about these studies and urge them to take about 6,000 IU/day. That would be about 5,000 IU for mom and 1,000 IU for the infant.