Quick answer

NIH's LactMed database says vitamin B12 is a normal component of human milk and that the breastfed infant is not exposed to excessive B12 when a mother with a deficiency takes higher doses. It also says low doses in B complex or prenatal vitamins raise milk levels only slightly. Ask your doctor before supplementing.¹

Key facts

LactMed says vitamin B12 is a normal component of human milk.¹
LactMed says low doses found in B complex or prenatal vitamins increase milk levels only slightly.¹
LactMed says the breastfed infant is not exposed to excessive B12 when a mother takes higher doses for a deficiency.¹
NIH says exclusively breastfed infants of women who eat no animal products can develop B12 deficiency very early in life.²
The label of a B12 injection says B12 is excreted in human milk, and deficiency has been recognized in breastfed infants of vegetarian mothers who had no symptoms.³

What does LactMed say about vitamin B12 and nursing?

LactMed is the National Library of Medicine's database of medicines and supplements during breastfeeding. Its entry on vitamin B12, updated in March 2025, says B12 is a normal component of human milk. It adds that supplementation may be needed to reach the recommended intakes or to correct a known deficiency.¹

On how much reaches milk, the entry is specific. Low doses, such as those in a B complex or prenatal vitamin, raise milk levels only slightly, while higher daily doses are needed when the mother is deficient. It says the breastfed infant is not exposed to excessive B12 in those cases, and that the infant's own B12 status should rise if it was low.¹

What happens to infants of mothers with low B12?

The concern in the sources is deficiency, not excess. LactMed lists the poor outcomes in infants with B12 deficiency as anemia, abnormal skin and hair development, convulsions, weak muscle tone, failure to thrive, mental developmental delay and abnormal movements. It names exclusively breastfed infants of mothers with little or no animal food in the diet, or with pernicious anemia, as the well-recognized at-risk groups.¹

NIH's professional fact sheet says the same, and adds that the mother's own deficiency can be mild and unrecognized. A label for B12 injections makes the same point: deficiency has been recognized in breastfed infants of vegetarian mothers even though the mothers had no symptoms at the time.^2,3

Breastfed babies of women who eat no animal products can have very limited B12 reserves, because little B12 reaches them through the placenta and breast milk.²

What do NIH and the label say about milk?

NIH's professional sheet lists a recommended intake in lactation that is higher than for other adults, and it sets no upper limit for B12 at any life stage. It also reports the typical level of B12 in the milk of women who get more than the recommended amount.²

The breast milk of women who get more than the recommended amount of B12 averages 0.44 mcg per liter.²

The injection label says vitamin B12 is known to be excreted in human milk, and elsewhere says the need for B12 is increased by pregnancy and lactation.³

Who should ask a doctor before taking vitamin B12 while breastfeeding?

Anyone who eats no animal foods, since the infant's B12 depends on the mother's.^1,2
Anyone with pernicious anemia, a stomach or bowel condition or past stomach surgery.^1,2
Anyone taking metformin or a proton pump inhibitor, which can lower B12 levels.²
A parent whose baby has poor weight gain, weak muscle tone or missed developmental milestones, who should ask the baby's doctor and mention what the mother eats and takes.^1,2

Questions people ask

Is vitamin B12 safe while breastfeeding?

LactMed says B12 is a normal part of human milk and that the breastfed infant is not exposed to excessive B12 when a deficient mother takes higher doses. Ask your doctor about your own diet and supplement.¹

Are b vitamins safe while breastfeeding?

For B12, LactMed says the low doses in a B complex or prenatal vitamin raise milk levels only slightly. LactMed has a separate entry for B6, which our vitamin B6 page covers. Ask your doctor or pharmacist to check a B complex label.¹

Can you take b12 supplements while breastfeeding?

LactMed says supplementation may be needed to reach recommended intakes or to correct a known deficiency, and describes no exposure to excess in the infant. Ask your doctor, especially if you eat no animal foods.¹

Can I take b12 while breastfeeding if I am vegan?

NIH says exclusively breastfed infants of mothers who eat no animal products can develop B12 deficiency very early, and that the mother's own deficiency may be mild. Ask your doctor and your baby's doctor.²

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line

Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.