You may have heard or been told that all breastfed babies need 400 IU/day of vitamin D supplementation. While this is true, I wanted to provide a bit more information regarding the reasoning. My qualm with this is that sometimes, I think it sends us the message that our breastmilk is subpar. I know when I learned this I thought, "Hmm, so formula has more vitamin D than breastmilk?" and then my next thought was, "How did babies survive on breastmilk prior to the invention of vitamin D3 supplements?". There's much more to it than that and I'm here to share this topic in a more comprehensive way. But first, the truth is human milk is the perfect food for human babies. Okay, here's a bit more info.

Vitamin D is an important nutrient for optimizing calcium absorption. This promotes healthy bone growth and maintenance and prevents things like rickets (in children) and osteoporosis (in adults). Sufficient vitamin D may also be linked to a decreased risk for certain cancers, high blood pressure, certain autoimmune diseases such as multiple sclerosis and rheumatoid arthritis, and diabetes.

Our bodies make vitamin D from sun exposure, but in our modern world and with an emphasis on skin cancer protection, many of us are not spending time outside regularly and when we are, we are lathering on the sun screen.

Dietary sources of calcium include things like cod liver oil, tuna, mackerel and salmon, egg yolk, beef liver, and fortified dairy products. Often this isn't enough though, or these foods aren't consumed regularly enough.

Therefore, supplementation is often recommended. The American Academy of Pediatrics (AAP) and Academy for Breastfeeding Medicine recommend breastfed babies be supplemented with vitamin D, as adequate sun exposure is hard to measure and often unlikely. However, a lot of emphasis is put on supplementing baby - newborns should receive 400 IU of vitamin D3 per day from birth to 1 year. We don't often hear about mom supplementing. Curious right?

Remember, mom and baby are a dyad. They have a very symbiotic relationship. Interestingly, research shows that maternal vitamin D supplementation can help ensure adequate intake for both mom and baby without supplementation for baby being required. It's not that human milk has this weird defect and doesn't contain vitamin D (which is often how this topic is presented), but rather that maternal intake is not adequate and the true vitamin D needs of a lactating mother are not addressed. More recent research tells us "the inherent flaw is not the design of human milk but in the vitamin D recommendation with respect to the lactating mother" (Hollis et al., 2015). Specifically, maternal supplementation of 6400 IU/day of vitamin D3 has been shown to allow sufficient vitamin D in breast milk. "With appropriate vitamin D intake, the lactating mother can fully transfer from her blood to her milk the vitamin D required to sustain optimal vitamin D nutrition in the nursing infant, with no additional supplementation required for the infant" (Hollis et al., 2015). It is not that breast milk lacks vitamin D, but that we the mother, may not be getting enough. The other benefit to maternal supplementation is that this also benefits mom. We know that bone metabolism is higher in lactating mothers. During lactation, our bodies' ability to absorb vitamin D is also increased, which means that any vitamin D we consume will be even better utilized. This means that if we consume adequate amounts of calcium and vitamin D during the breastfeeding period, our risk for osteoporosis is actually decreased later! Another bonus to breastfeeding for us mamas!

References:
Hollis, B.W. et al. (2015) Maternal versus infant vitamin D supplementation during lactation: A randomized controlled trial, Pediatrics. U.S. National Library of Medicine. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586731/#:~:text=With+appropriate+vitamin+D+intake,supplementation+required+for+the+infant (Accessed: January 5, 2023).

Vitamin D, your baby, and you (2020) La Leche League International. Available at: https://www.llli.org/breastfeeding-info/vitamin-d/#:~:text=A+rigorous+study+reported+that,strategy+to+direct+infant+supplementation.%E2%80%9D (Accessed: January 5, 2023).