Breastmilk is considered the perfect food and health authorities encourage women to breastfeed exclusively for the first six months and continue to breastfeed for as long as possible. Surely if Mum takes a vitamin supplement, there should be no issue with vitamin D for the baby?

Researchers have looked at this very question and here are their findings:[1]

  • Mothers who took vitamin D supplements at typical doses of 400 IU (10mg) per day while breastfeeding do not seem to pass enough vitamin D in their breastmilk.
  • Most multivitamins and prenatal supplements contain 400 IU per dose.
  • Past studies show that breastmilk of normal healthy mothers contains only 5-80 IU/L. To put this in perspective, a baby needs 400 IU per day!
  • Researchers found that a dose of 6400 IU (160 mg) per day for mothers provides enough circulating vitamin D to be able to supply her baby with the required amount through breast milk.
  • The daily dose of 6400 IU is much higher than public health recommendations for adults, which is 600 IU per day. As a precaution, health authorities recommend a daily vitamin D supplement for breastfed infants.
  • Health authorities recommend that lactating mothers continue to take vitamin supplements to ensure that they remain healthy.

The question remains: why would Mother Nature design breastmilk to be low in vitamin D?

The quick answer is that human breastmilk is not defective! The way that we live has changed. The general population does not consistently make enough vitamin D from direct sunlight during their daily living.

A deeper dive into science explains the mystery of vitamin D in human breastmilk (1):

  • The vitamin D supplement molecule that we make in our skin from sunshine or take in a supplement can pass from mother’s blood supply into breastmilk.
  • This initial form of vitamin D stays in the bloodstream for a short period of time, only 12-24 hrs.
  • Scientists believe that to keep this original vitamin D version in a mother’s bloodstream, a daily vitamin D supplement at a higher amount is required to pass this nutrient into breastmilk.
  • Our bodies begin to break down the initial vitamin D within 12 to 24 hours. The by-product or metabolite of vitamin D, 25-OH vitamin D, does not seem to pass into human breastmilk.
  • This metabolite stays in the blood system much longer and is used as a marker to test vitamin D blood levels.
  • If a mother’s blood test shows a healthy range of the 25-OH vitamin D, she could still not have the right amount of the original version in her bloodstream to pass to the baby!
  • As a precaution, a daily vitamin D supplement for breastfed babies is a standard recommendation in most countries

Why is vitamin D a big deal now and it was not an issue in past generations?

  • Many generations ago, our ancestors likely lived in climates that were warm and sunny, keeping safe from bitter cold long winters
  • They were outside in direct sunlight pretty much every day, doing activities like walking outside, farming, building etc. They did not spend time inside in air conditioning, nor did they have sunscreen
  • With this daily sun exposure on their skin, they made their own vitamin D molecules in consistently high amounts, that supported growth and development of healthy bones and teeth.
  • These vitamin D molecules could pass into mothers’ breastmilk in sufficient amounts to keep the adequate levels in breastmilk
  • Now that things have changed and people can live successfully in areas that do not have consistently pleasant weather. Industrialization means many people work indoors, and transportation is in covered, protected vehicles.
  • Researchers and health authorities are noticing that our population may not have the same levels of vitamin D as previous generations. This is why some foods are fortified with vitamin D and a vitamin D supplement is often recommended, especially in industrialized areas of the world.

Be sure to check with your healthcare practitioner for their advice on supplementing yourself and your baby.

[1]Hollis, B., et al. Maternal Versus Infant Vitamin D Supplementation During Lactation: A Randomized Controlled Trial. Pediatrics 2015;136;625 DOI: 10.1542/peds.2015-1669