Nobody Told Me That Despite Everything Breastmilk Does, It Doesn’t Do Vitamin D

This article is part of the Nella Vosk Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide for Australian Mothers — your comprehensive resource on nourishing yourself and your baby through every stage of the feeding journey.

This article is part of Nella Vosk’s Nobody Told Me series — a growing collection of posts about the information gap that too many mothers encounter after birth. Every article in this series starts from a moment a mother wasn’t told something she needed to know, and works back through the clinical truth behind it. You can find the full series at nellavosk.com.au/pages/nobody-told-me. This is the final post in Chapter 1 — Nourish Mama. Chapter 2, Bamboo Bubby, begins next.

Nobody told me that despite everything breastmilk does, it doesn’t do vitamin D.

I had spent months reading about breastmilk. Its immune properties. Its live cells and antibodies. Its dynamic composition that changes within a feed, across the day, and in response to my baby’s illness. I understood breastmilk to be, in every meaningful sense, complete. The most nutritionally sophisticated substance produced by the human body, calibrated over millions of years of evolution to perfectly match what a human infant needs.

And then someone mentioned, almost in passing, that breastfed babies in Australia might need vitamin D drops. That breastmilk — this miraculous, irreplaceable, evolutionarily perfect substance — was not providing adequate vitamin D. And that in a country famous for its sunshine, vitamin D deficiency in breastfed infants was a real and documented clinical concern.

This post explains why — the evolutionary reason breastmilk is low in vitamin D, what this means for babies in Australia specifically, what both mothers and babies need to do about it, and the maternal vitamin D picture that sits behind this story.

Why Breastmilk Is Low in Vitamin D

The question of why breastmilk — otherwise extraordinarily complete — is low in vitamin D is one of the more interesting puzzles in nutritional biology, and the answer lies in evolutionary history.

For most of human evolutionary history, infants were carried against the skin of their caregivers in warm climates, with regular skin exposure to sunlight. Vitamin D is not, in the strict sense, a dietary nutrient — it is a prohormone that the body synthesises in the skin in response to ultraviolet B radiation from sunlight. Because infants in the evolutionary environment were reliably sun-exposed through skin-to-skin carrying, there was no evolutionary pressure to deliver substantial vitamin D through breast milk. The sun was the source. Breastmilk was not required to provide it.

The modern environment has profoundly changed this picture. Contemporary infants spend the majority of their time indoors, covered by clothing and blankets, protected by carseats and prams with sunshades, in climates and latitudes where UVB radiation is seasonal or insufficient for adequate skin synthesis. The evolutionary assumption that infants would receive sun exposure has not held, and breastmilk has not evolved fast enough to compensate.

The result is a genuine mismatch: breastmilk, which evolved in a world where infants were reliably sun-exposed, is nutritionally complete for every purpose except vitamin D — which evolution assumed the sun would provide. In the modern indoor world, it often doesn’t.

Does Breast Milk Have Enough Vitamin D?

No — not typically, and not for the majority of breastfed infants in Australia when considered against current recommendations.

The vitamin D concentration in breast milk is directly determined by the mother’s own vitamin D status. A mother with replete vitamin D levels (serum 25-hydroxyvitamin D above 75 nmol/L) produces milk with higher vitamin D concentrations than a mother who is deficient. But even at optimal maternal vitamin D status, the concentration in breast milk is low enough that an exclusively breastfed infant consuming a typical volume of milk per day (approximately 750 to 800ml) would receive well below the recommended daily intake for infants.

The NHMRC Nutrient Reference Values for Australia and New Zealand set the adequate intake of vitamin D for infants as 5 micrograms (200 IU) per day. Research consistently finds that breast milk from mothers with typical vitamin D status provides far less than this — often only 1 to 2 IU per 100ml of milk, meaning a breastfed infant consuming 750ml per day receives approximately 7 to 15 IU daily against a recommended intake of 200 IU.

This gap is not an argument against breastfeeding. It is an argument for targeted vitamin D supplementation of breastfed infants and/or high-dose maternal supplementation to increase milk vitamin D concentrations — both of which are evidence-based strategies with clear recommendations from major health bodies.

Vitamin D Deficiency in Australia: The Irony of the Sunburnt Country

Australia has some of the highest UVB radiation on earth. It also has rates of vitamin D deficiency that surprise most people when they first encounter them.

Research from the Australian Bureau of Statistics and the Australian Institute of Health and Welfare consistently shows that a meaningful proportion of Australian adults — including women of reproductive age — have vitamin D levels below the 50 nmol/L threshold considered adequate. The rates are higher in southern states (Victoria, Tasmania, South Australia), in women with darker skin (who require longer sun exposure to produce the same vitamin D as people with lighter skin), in women who cover their skin for religious or cultural reasons, and in mothers of newborns who are largely indoors during the demanding early weeks and months of new parenthood.

Postpartum vitamin D deficiency is particularly common for a combination of reasons:

• Pregnancy itself draws on maternal vitamin D stores for foetal skeletal development

• The early months of newborn care are typically spent predominantly indoors

• Breastfeeding transfers some vitamin D to the baby (though the total amount is modest), adding to maternal depletion

• New mothers are often too fatigued to pursue deliberate sun exposure, and when they do go outside, the baby is appropriately covered and protected from direct sun

A mother who is vitamin D deficient cannot produce vitamin D-replete breast milk. Addressing maternal vitamin D status is therefore both a maternal health issue and a breastfeeding health issue.

What Low Vitamin D in Breast Milk Means for Breastfed Babies

Vitamin D is essential for:

• Calcium absorption and bone mineralisation: the most clinically significant consequence of severe vitamin D deficiency in infancy is rickets — a condition characterised by soft bones, skeletal deformity, and impaired growth. While frank rickets is uncommon in Australia, subclinical vitamin D insufficiency is not

• Immune function: vitamin D is a significant modulator of the immune system, and deficiency in early life has been associated in research with increased susceptibility to respiratory infections and altered immune development

• Muscle function and motor development

• Neurological development: emerging research suggests vitamin D has roles in brain development and may be relevant to neurodevelopmental outcomes, though this area of research is still developing

The Royal Australasian College of Physicians and the Royal Australian College of General Practitioners both recommend vitamin D supplementation for exclusively breastfed infants who are at risk of deficiency. The Australian Breastfeeding Association also notes that breastfed babies who have limited sun exposure should receive a vitamin D supplement.

Should Breastfed Babies Get Vitamin D Drops in Australia?

For many breastfed infants in Australia, yes — though the specific recommendation depends on several factors that are worth understanding:

High-risk infants who should supplement

• Infants of mothers with low vitamin D status

• Infants with darker skin pigmentation, who require longer sun exposure to produce equivalent vitamin D

• Infants in southern Australian states (Victoria, South Australia, Tasmania) during autumn and winter, when UVB radiation is insufficient for skin vitamin D synthesis for much of the day

• Infants who are kept covered or indoors consistently (as most newborns are in the early weeks for practical and safety reasons)

• Premature infants, who may have lower vitamin D stores from limited third-trimester transfer

The standard Australian recommendation

The standard supplementation dose for infants is 400 IU (10 micrograms) of vitamin D3 daily, which aligns with recommendations from the American Academy of Pediatrics (which is widely referenced in Australian paediatric practice) and is considered safe and effective for addressing the gap between breast milk vitamin D content and infant requirements.

Vitamin D drops for infants are available over the counter in Australian pharmacies. Discuss with your GP or maternal and child health nurse whether supplementation is appropriate for your baby, particularly if you are in a southern state, your baby has darker skin, or you have reason to believe your own vitamin D levels may be low.

Can I Take Vitamin D Supplements While Breastfeeding?

Yes — and there is a specific reason to do so beyond the general maternal depletion picture.

Research has demonstrated that maternal high-dose vitamin D supplementation can meaningfully increase the vitamin D concentration in breast milk. A landmark randomised controlled trial by Hollis et al. (2015) found that lactating mothers supplementing with 6,400 IU of vitamin D3 per day produced milk with sufficient vitamin D to meet their exclusively breastfed infant’s needs without requiring the infant to take drops separately. This approach — high-dose maternal supplementation to fortify breast milk — is an evidence-based alternative to infant drops that some mothers and families prefer.

The standard adult recommended dietary intake for vitamin D in Australia is 5 micrograms (200 IU) per day for women aged 19 to 50. For breastfeeding women with confirmed or likely deficiency, supplementation at higher doses — typically 1,000 to 2,000 IU per day for general correction, or up to 6,400 IU per day if the specific goal is fortifying breast milk for the baby — is appropriate under GP guidance.

The upper tolerable intake for vitamin D in adults is 80 micrograms (3,200 IU) per day in the NHMRC framework, though some international bodies set this higher. Before taking high-dose vitamin D, a blood test to check your current 25-hydroxyvitamin D level is the most useful guide to how much supplementation is appropriate.

Can Low Vitamin D Cause Low Milk Supply?

This is a question that appears regularly in breastfeeding communities, and the evidence is suggestive rather than definitive. Several mechanisms have been proposed by which low maternal vitamin D might impair milk production:

• Vitamin D receptors are present in mammary gland tissue, and there is some evidence that vitamin D signalling plays a role in mammary gland development and function

• Vitamin D deficiency is associated with fatigue, low mood, and immune dysfunction — all of which may indirectly affect breastfeeding sustainability even if they do not directly affect milk volume

• Some case reports describe improved milk supply following correction of maternal vitamin D deficiency, though controlled trial evidence is lacking

The honest answer is that the direct evidence for vitamin D deficiency causing reduced milk supply is limited. What is more clearly established is that maternal vitamin D deficiency is a legitimate clinical concern in its own right — for maternal bone health, immune function, mood, and general postpartum recovery — and is worth addressing regardless of whether it directly affects supply.

Sun Exposure for Breastfed Babies: What It Actually Achieves

Many mothers are told that their baby can get adequate vitamin D from sunlight, and this is technically true under specific conditions. But those conditions are narrow and often impractical:

• The UVB radiation that triggers skin vitamin D synthesis is present in sufficient intensity in most Australian cities only during certain times of day (roughly 10am to 3pm) and only during certain months (May to August is insufficient at latitudes south of approximately Brisbane)

• Only a small amount of skin needs to be exposed — face, arms, and legs — but exposing a young infant’s skin to direct sunlight carries significant UV damage risk. Sunscreen blocks vitamin D synthesis; hats and clothing block it. Shade reduces it substantially

• Current skin cancer prevention guidelines in Australia recommend sun protection for all children under 12 months and advise against deliberate sun exposure of infants, which directly conflicts with the vitamin D synthesis requirement

The practical conclusion is that sun exposure is not a reliable vitamin D source for young infants in Australia, particularly in southern states or winter months, and supplementation is the safer, more predictable approach.

Maternal Vitamin D: The Picture Beyond the Baby

Everything discussed above about vitamin D and breast milk is primarily about the baby’s needs. But the mother’s own vitamin D status deserves attention independently.

Maternal vitamin D deficiency postpartum is associated with:

• Increased bone resorption: particularly relevant in the context of lactational amenorrhea and its oestrogen-deficient state, which already elevates bone turnover. Low vitamin D in this context compounds the bone density risk

• Postpartum fatigue and mood disturbance: vitamin D deficiency is independently associated with low mood, fatigue, and cognitive difficulty — symptoms that are also common postpartum for many other reasons, making deficiency easy to miss

• Immune vulnerability: postpartum immune function is already transitioning; vitamin D deficiency adds to the susceptibility to respiratory infections, recurrent mastitis, and other infections that some mothers experience in the first postpartum year

• Postpartum thyroiditis risk: vitamin D has immunomodulatory effects, and there is evidence of an association between vitamin D deficiency and autoimmune thyroid conditions including postpartum thyroiditis (affecting 5 to 10% of postpartum women)

Requesting a vitamin D check at or after the six-week postnatal appointment is worthwhile for most Australian breastfeeding mothers, particularly if they are in a southern state, have darker skin, or have been spending significant time indoors. For the broader picture of postpartum nutritional status and what blood tests to request, the article on signs of postpartum depletion covers the complete recommended panel.

Food Sources of Vitamin D for Breastfeeding Mothers

Vitamin D from food is limited but worth maximising:

• Oily fish: by far the richest dietary source. Salmon provides approximately 10 to 18 micrograms per 100g serving; sardines approximately 5 to 12 micrograms; canned tuna approximately 2 to 5 micrograms. Eating oily fish two to three times per week supports both vitamin D and DHA intake

• Eggs: the yolk contains vitamin D at approximately 1 to 2 micrograms per egg, with significantly higher levels in eggs from hens raised outdoors with sun exposure

• UV-exposed mushrooms: mushrooms that have been exposed to UV light (or sunlight) generate vitamin D2. Some commercially available mushrooms in Australia are sold as “UVB-treated” or “sun-dried” for this purpose. A serve can provide meaningful vitamin D if specifically sourced for this property

• Fortified foods: in Australia, margarine is fortified with vitamin D by law; some plant milks are voluntarily fortified. These provide modest but consistent contributions to daily intake

Food alone is unlikely to be sufficient to address vitamin D deficiency, particularly in the postpartum period. Supplementation alongside food sources is the realistic approach for most mothers.

This is the final post in Chapter 1 of the Nobody Told Me series — Nourish Mama. Twenty-two posts about what the postpartum breastfeeding body actually needs, and what the system consistently fails to communicate. Chapter 2 — Bamboo Bubby — begins with the first post about baby eczema, skin triggers, and the information gap that keeps parents blaming themselves.

Keep Reading

These posts connect to the postpartum nutritional picture:

Signs of Postpartum Depletion (And What to Do)

Postpartum Nutrition & Recovery: Complete Guide for New Mothers

From Colostrum to Mature Milk: The Stages of Breastmilk Production

Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide

Nobody Told Me That Zinc Was Quietly Running Low

Best Postpartum Snacks for Energy and Milk Supply

Postpartum Allergies: Why They Happen & What to Do

Breastmilk is extraordinary. And it still needs a little help with vitamin D. The Nella Vosk postpartum recovery range is formulated by a Certified Postpartum Nutrition Professional who has spent fourteen years in the nutritional gap between what breastfeeding mothers are told they need and what they actually need — including the nutrients that even the most complete food on earth cannot deliver on its own.

ABOUT THE AUTHOR

Kelly Northey is a Certified Postpartum Nutrition Professional (CPPNP) and founder of Nella Vosk, an Australian maternal and family wellness brand. She specialises in breastfeeding nutrition, postpartum recovery, and the evidence behind what Australian mothers actually need — and aren’t being told.
Learn more about Kelly.