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Vitamin D in breastmilk

Breast milk contains all the nutrients a healthy, full-term baby needs during about the first six months of life. In the second half of the first year, other foods than breastmilk are slowly introduced. This time is a learning period for babies who should learn to master how to put food in their mouth, chew and swallow. Breast milk is still the staple food at this time.

Recently, the American Academy of Pediatricians (AAP) released a report recommending supplementation of vitamin D for all breastfed infants in the US. Does this mean that breast milk does no longer provide all the vitamins and minerals a baby needs? Let's take a look at this.

Where does the vitamin D come from?

In fact, vitamin D is not a vitamin, but a hormone. The precursor of this substance can be converted to what we call vitamin D. This happens in the skin under the influence of UVB radiation in sunlight. This is the natural way most human beings get sufficient vitamin D. Researchers previously estimated that daily exposure of small parts of the skin of European infants during 10 minutes would be sufficient to prevent deficiencies. Other sources that provide vitamin D may be fatty fish, fortified margarine and milk, eggs, butter. Besides sunlight, food is also considered a source of vitamin D. A mother with adequate nutrition gives her infant some vitamin D stores during pregnancy that carries to term. After that, in one way or the other a child should get vitamin D.
Breast milk does contain vitamin D in the range of 5 to 136 IU per liter. According to the AAP, infants should get 400 IU per day in the form of a supplement, preferably liquid drops. Exposure to sunlight can provide additional vitamin D, but exposing infants to sun light without protection against sunburn, is not recommended.

Breast milk and sun exposure

Let's assume that the amount of vitamin D in breast milk did not change over the centuries. Still, there appears nowadays to be a larger risk in infants to be deficient. Reasons for this deficiency may be:
Not living at the latitude that fits your skin color. People with a light skin at lower latitudes are likely to either avoid sun exposure to prevent sunburn, or use sunscreen, which protects against the effects of UVB, including production of vitamin D in the skin. People with a darker skin living at higher latitudes may not get the right amount of sun exposure, since their skin protects them against the effects of UVB radiation. In the winter, this effect is even stronger.
Sun exposure can further be inadequate as a result of clothing (to protect from cold, sun light or as a cultural norm), living indoors during daytime (including at daycare centers) and weather conditions.
In addition, it may be that in former times the amount of vitamin D in breast milk was higher due to more sun exposure. Also, researchers find that vitamin d protects against more diseases besides rickets, including certain cancers and cardiovascular disease. Also, vitamin D may help protect against depression. However, these protective effects happen at higher levels of vitamin D intake.

So over all, the amount of sun exposure changed and so did the production of vitamin D in the skin. The current recommendations of vitamin D supplementation stem from changes in our lifestyle regarding sun exposure and possibly our food intake.

What does vitamin D?

Vitamin D is necessary for the uptake of calcium and phosphates in the gut. An impaired uptake of vitamin D combined with a minimum exposure to sunshine can lead to rickets, a disease that affects the bone growth in young children. Currently, rickets is present in 9 per million infants, mainly in infants with a darker skin. Rickets in older children declined after the fortification of cows' milk.
New research suggests that vitamin D protects against more illnesses. It may be that the recommendations for supplementation will change again in the near future.


As of now, the AAP recommends that infants six months and under be not exposed to direct sunlight. After that, infants should be protected against UVB by application of sunscreen. To meet the requirements of vitamin D in infants and young children, supplementation of vitamin D is recommended by the AAP. By supplementing the infants, the effects of exclusive breastfeeding may be impaired. In children with severe allergies, administration of vitamin D drops may lead to problems. More research is needed to estimate the amount of safe and adequate sun exposure and safe and adequate vitamin D supplementation. What mothers and expectant women can do, is assure that their own levels of vitamin D are optimized by taking supplements themselves. A mother who had optimal serum levels during pregnancy and lactation, will produce milk with a higher level of vitamin D. Mothers can start working on optimal levels in breast milk prenatally or even preconception and continue to do so postpartum.

To supplement or not to supplement

Your pediatrician, or you yourself may want to know if your baby has adequate levels of vitamin D. this can be tested with a blood test. If you feel not comfortable with a blood test for your baby, you may suggest to get your own levels tested. If you test low, you can choose to test your baby and start supplements for yourself.

Making healthy choices

Consult your physician about your child 's risk factor for not meeting the vitamin D requirements and the need for supplementation.

Further reading:

Good Mojab, C. Sunlight deficiency: a review of the literature. Mothering 2003 Mar-Apr; 117:52-63
Passmore R. and Eastwood M.A. Davidson and Passmore Human Nutrition and Dietietics. 8th edition, 1986, New York, Churchill Livingstone
M. J. Heinig. Vitamin D and the Breastfed Infant: Controversies and Concerns. Journal of Human Lactation 19(3), 2003

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© 2003 Nanny Gortzak, updated September 2011