Quick answer
Women need 2.4 mcg of vitamin B12 a day, 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding. US women average 3.69 mcg from food, but 11% fall below the average requirement. After 50, NIH advises getting most B12 from fortified foods or supplements.1,2
Key facts
- About 29% of US women take a supplement that contains B12.2
- Women, people with low incomes and non-Hispanic Black people are the groups most likely to have low B12 intakes.2
- The recommended amount stays at 2.4 mcg a day for women over 50, 60 and 70.1
- B12 in supplements does not need stomach acid to be released from food protein.1
How much women need
| Stage | Recommended per day |
|---|---|
| Girls 14 to 18 | 2.4 mcg |
| Women 19 and over | 2.4 mcg |
| Pregnancy | 2.6 mcg |
| Breastfeeding | 2.8 mcg |
| Over 50 | 2.4 mcg, mostly from fortified foods or supplements |
What B12 does for women
B12 does the same jobs in women as in men. These are its established functions, graded moderate.
Contributes to normal red blood cell formation*2,3
Moderate evidence
NIH lists healthy red blood cell formation among B12's core jobs, and the US recommended amount was set as the intake needed to keep blood counts and blood B12 levels normal. Without enough B12, the body makes large, abnormal red blood cells. The EU permits this statement.
Amount studied: Recommended intake: 2.4 mcg a day for adults, from all sources
Contributes to normal functioning of the nervous system*2,3
Moderate evidence
NIH describes B12 as required for the development, myelination and function of the central nervous system; myelin is the coating around nerve fibers. The EU permits this statement. In trials summarized by NIH, B12 supplements given alone or with other B vitamins for 1 to 5 years did not change measures of memory and thinking in older adults.
Amount studied: Recommended intake: 2.4 mcg a day for adults, from all sources
In your 30s and 40s
At this age food usually covers it: US women average about 3.7 mcg a day from food, well over 2.4 mcg. The common exceptions involve diet, surgery and medicines: vegan or mostly plant-based eating, past weight-loss surgery, and long-term use of metformin or acid reducers.1,2
If you eat no animal foods, fortified foods or a supplement are the reliable sources, because B12 occurs naturally only in animal foods.2
Pregnancy and breastfeeding
The recommended amount is 2.6 mcg a day during pregnancy and 2.8 mcg while breastfeeding.1
Blood B12 levels tend to fall during pregnancy, sometimes below normal, and usually return to normal after delivery.2
The breast milk of women who get more than the recommended amount of B12 averages 0.44 mcg per liter.2
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
Over 50, 60 and 70
The amount stays at 2.4 mcg at every age after 14. What changes is absorption: many older adults make too little stomach acid to release B12 from food, which is why NIH advises people over 50 to rely mostly on fortified foods or supplements.1
Among adults aged 60 and over, about 3.7% have blood B12 below 200 pg/mL and about 12.3% below 300 pg/mL.2
Cautions for women
Pernicious anemia, an autoimmune condition in which the stomach stops making intrinsic factor, is more common in women and in people of European ancestry. It causes low B12 even with a good diet, and doctors usually treat it with B12 shots.1,2
Atrophic gastritis, which cuts stomach acid and intrinsic factor, affects about 2% of people overall but 8% to 9% of adults aged 65 and over.2
In pregnancy and breastfeeding, low B12 might cause neural tube defects, developmental delays, failure to thrive and anemia in the baby. Breastfed babies of vegan mothers can become deficient very early in life.2
- Ask first if you take metformin or a medicine for acid reflux
- See a doctor about numbness, tingling, balance problems or memory changes, which can come from low B121
- Ask first if you are pregnant or breastfeeding and eat no animal foods
Questions people ask
Should women over 50 take a B12 supplement?
NIH advises everyone over 50 to get most of their B12 from fortified foods or supplements, because most people that age can absorb B12 from those sources. Either route works, and a blood test can show whether you need more.1
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Sources
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Consumers. Updated December 15, 2023. Opened 2026-10-07.
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. Updated July 2, 2025. Opened 2026-10-07.
- European Commission. Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods. Official Journal of the European Union, L 136, 25.5.2012, p. 1. Opened 2026-10-07.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.