Quick answer

Women need slightly less thiamin, riboflavin and niacin than men, but needs for most B vitamins rise in pregnancy and breastfeeding. NIH advises women who could become pregnant to get 400 mcg of folic acid a day, and women over 50 to get most vitamin B12 from fortified foods or supplements.^1,2,3

Key facts

Even counting supplements, 17% of women aged 19 to 30 do not reach the average folate requirement.⁴
Women's vitamin B6 needs rise from 1.3 mg to 1.5 mg a day at age 51.⁵
Prenatal vitamins and most multivitamins already contain folic acid and other B vitamins.^2,5
Breastfed babies of mothers who eat no animal foods can run short of vitamin B12.³

How needs change through life

What rises for women, compared with the usual adult amounts^{1,2,3,5,6,7,8,9}
Stage	What changes
Pregnancy	Folate rises to 600 mcg DFE, vitamin B6 to 1.9 mg, vitamin B12 to 2.6 mcg, thiamin and riboflavin to 1.4 mg each, niacin to 18 mg NE and pantothenic acid to 6 mg. Biotin stays at 30 mcg.
Breastfeeding	Folate is 500 mcg DFE, vitamin B6 2.0 mg, vitamin B12 2.8 mcg, riboflavin 1.6 mg, thiamin 1.4 mg, niacin 17 mg NE, pantothenic acid 7 mg and biotin 35 mcg.
Age 51 and older	Vitamin B6 rises to 1.5 mg, and most vitamin B12 should come from fortified foods or supplements.

Outside pregnancy and breastfeeding, women need 1.1 mg of thiamin, 1.1 mg of riboflavin and 14 mg NE of niacin a day, a little less than men. The other B vitamin amounts are the same for both.^1,6,7

Turning 30, 40 or 60 does not change the amounts. The steps come at 19, at 51, and during pregnancy and breastfeeding.¹⁰

Folic acid if you could become pregnant

NIH advises all women and teen girls who could become pregnant to get 400 mcg of folic acid a day from supplements, fortified foods or both, on top of the folate in a varied diet.^2,10

The advice covers every woman who could become pregnant, not only those planning to, because about half of all pregnancies are unplanned. For this purpose the CDC advises folic acid itself rather than methylfolate, even for women with an MTHFR gene variant.^2,4

Teens and women in their 20s

Even counting supplements, 19% of girls aged 14 to 18 and 17% of women aged 19 to 30 do not reach the average folate requirement, and 23% of non-Hispanic Black women fall short.⁴

Folate from food, folic acid in enriched grains and folic acid from a supplement all count toward the target, so a young woman who eats few fortified grains or leafy greens can fall short without noticing.²

Women over 50

Two things change after 50. Vitamin B6 needs rise a little, and NIH advises getting most vitamin B12 from fortified foods or supplements, because many older adults absorb less of the B12 that is bound to protein in food.^3,5

Between 3% and 43% of older adults are low in vitamin B12, depending on how it is measured.^3,11

Vegetarian and vegan women

Women who eat no animal foods need fortified foods or a supplement for vitamin B12. This matters most in pregnancy and breastfeeding, because a mother who is short of B12 can pass that shortage to her baby.^3,11

Riboflavin is the other B vitamin more likely to run short in women who avoid dairy, so fortified cereals, mushrooms, spinach and almonds are worth knowing about.^6,12

Medicines, tests and who should ask first

Large amounts of folic acid can correct the anemia caused by a vitamin B12 deficiency while the nerve damage continues, which can delay the diagnosis, and may make the deficiency worse. This is the basis of the upper limit for folic acid.^2,4

Exclusively breastfed babies of mothers who eat no animal foods can develop vitamin B12 deficiency early in life, which can cause neurological damage and anemia if it is not found and treated.¹¹

If you are planning a pregnancy, ask your doctor about folic acid
If you are pregnant or breastfeeding, ask before adding a B complex to a prenatal vitamin
If you take methotrexate or an anticonvulsant, ask before any product with folic acid^4,13
If you have thyroid or hormone tests coming up, check whether your B complex contains biotin and tell the lab^9,14
If you take metformin or an acid reducer long term, ask whether your vitamin B12 should be checked^15,16

Questions people ask

What does B complex do for women?

The same things it does for men: B vitamins help release energy from food and make DNA and red blood cells. What differs for women is how much is needed at each stage, and the folic acid advice for anyone who could become pregnant.^2,3

Should women over 40 take a B complex?

Turning 40 does not change B vitamin needs, and a varied diet covers most women. Ask your doctor if you eat little animal food, are planning a pregnancy, or take a medicine such as metformin that can lower vitamin B12.^11,15

Can I take a B complex with a prenatal vitamin?

Ask your doctor or midwife first. Prenatal vitamins already contain folic acid and often other B vitamins, and folic acid has an upper limit of 1,000 mcg a day from supplements and fortified foods.^2,10

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