It just never made sense to me, 40 years ago, when my professors at UNC School of Medicine casually announced human breast milk contained no vitamin D.
“How can that be? How can that possibly be? That makes no sense,” I thought. “Was primitive man supposed to give their infants vitamin D pills that didn’t even exist?”
I have written before about biomarkers, such as:
- How high does your vitamin D level have to be to maximally suppress parathyroid hormone?
- How high does your vitamin D level have to be to maximally improve calcium absorption?
- How high does your vitamin D level have to be to prevent abnormal bones?
The answer to these questions varies from 20 ng/ml to 40 ng/ml, depending on what study you decide to quote. But what about breast milk as a biomarker? Infants need vitamin D for strong bones and general development. Without vitamin D, the infant can develop rickets. In the 21st century, this is treatable in a clinic. In the wild, the tribe may have left a screaming baby with soft bones at the wayside.
How high does the breastfeeding mom’s vitamin D level need to be for her infant to get natural vitamin D levels? This level is a biomarker because it gives us insight on how high vitamin D levels were for species survival. If the breastfeeding mom couldn’t supply vitamin D to the infant, our species may not have survived. Whatever vitamin D level that might be, that would be the level humans evolved to have.
Professors Wagner and Hollis and colleagues did an elegant randomized controlled trial 6 years ago that we have covered before, but it should be covered often. They simply gave two different doses of vitamin D to nursing mothers and measured the vitamin D levels of their infants and mothers. They used a small sample of breast feeding women, giving half the women a prenatal vitamin (containing 400 IU) and the other half a prenatal vitamin plus an extra 6,000 IU/day of vitamin D.
The suckling infants of the mothers given only the prenatal were also given 300 IU of vitamin D directly (it would have been unethical to deprive any of the infants of vitamin D). They noted no side effects with any dose, but the 6,000 IU/day arm of the study answered my 40-year-old question.
Wagner CL, Hulsey TC, Fanning D, Ebeling M, Hollis BW. High-dose vitamin D3 supplementation in a cohort of breastfeeding mothers and their infants: a 6-month follow-up pilot study. Breastfeed Med. 2006 Summer;1(2):59-70.
The 6,000 IU/day dose of vitamin D did three things.
- It gave the mothers natural vitamin D levels (50 ng/ml or close to).
- It transformed breast milk into a rich source of vitamin D.
- It gave suckling infants natural blood levels of vitamin D (45 ng/ml).
Given this, if you are now breast-feeding and not taking vitamin D, then I hope you are giving your infant at least 400 IU of vitamin D per day as the American Academy of Pediatrics (AAP) recommends. If you want your infant to start getting their vitamin D from your breast milk, I recommend the following steps:
- Take a loading dose of 10,000 IU/day for a month.
- After one month on 10,000 IU/day, stop supplementing your infant with vitamin D as your breast milk should now be filled with vitamin D.
- Take 6,000 IU/day maintenance dose thereafter, except on days you get full body sun exposure.
However — and this is important — when the breastfeeding stops, you need to start supplementing your child again, as the AAP recommends, unless the child is in the sun enough to have adequate levels, and very few are.
I’d like to reiterate, can you think of a better biomarker for how much vitamin D humans need?
- “How much vitamin D do human breast–feeding mothers have to take to transform their breast milk into an adequate source of vitamin D for their infants?”
This is a great biomarker question, one essential to the survival of our species. The answer is 50 ng/ml, which can be achieved by 6,000 IU/day for breastfeeding mothers.