Quick answer

Adult women need 1.1 mg of thiamine a day, teen girls 1.0 mg, and 1.4 mg during pregnancy and while breastfeeding. Most women get enough from food, averaging about 1.39 mg a day before supplements. The vitamin does the same job in women as in men; what changes with life stage is the amount.^1,2

Key facts

Pregnancy raises the US recommendation by 0.3 mg a day, from 1.1 to 1.4 mg.¹
An exclusively breastfed baby receives about 0.15 mg of thiamin a day from milk.³
Counting supplements, women in the United States average about 4.9 mg of thiamin a day.²
European reference values do not separate women from men: they scale with energy intake.³

How much girls and women need

Thiamin for girls and women, per day^1,2
Life stage	US recommended amount
Girls 9 to 13	0.9 mg
Girls 14 to 18	1.0 mg
Women 19 and over	1.1 mg
Pregnant teens and women	1.4 mg
Breastfeeding teens and women	1.4 mg

The amount for women stays at 1.1 mg after age 50. In Europe the reference for pregnancy and breastfeeding is the same 0.4 mg per 1,000 kcal used for every adult, so a woman's amount rises only as she eats more energy.^2,3

What women actually get

Women in the United States average 1.39 mg of thiamin a day from food alone, above the 1.1 mg they need, and about 4.9 mg once supplements are counted. National survey data suggest only about 6% of people fall short of the average requirement, although that figure is not reported separately for women.²

So for most women, thiamin is not the nutrient to worry about. The exceptions are the situations in the safety notes below, where intake drops or losses rise.²

Thiamine and breastfeeding

A mother's thiamin intake changes the thiamin in her breast milk very little unless she is short of it: milk from mothers taking 1.7 mg a day in a multivitamin had about 10% more.³

Mature breast milk from healthy mothers in Western countries carries 0.14 to 0.22 mg of thiamin per liter, and the first milk carries less. At about 0.8 liters a day, that is roughly 0.15 mg for the baby.^2,3

Pregnancy with severe or lasting vomiting

Severe, prolonged vomiting in pregnancy, called hyperemesis gravidarum, can drain thiamin quickly, because the body stores so little. A review of 177 published cases of Wernicke's encephalopathy in pregnancy found that it appeared at 10 to 15 weeks, after a median of 7 weeks of vomiting, and that thiamin was often given in too small a dose or not at all.^2,4

If you are pregnant and cannot keep food or fluids down, contact your doctor or midwife promptly. In that situation thiamin is given under medical care, often by injection.^4,5

The injectable thiamin label notes that studies in pregnant women have not shown that thiamin raises the risk of fetal abnormalities. Because they cannot rule out harm, the label says to use it in pregnancy only if clearly needed.⁵

Other reasons to ask first

You have had bariatric surgery: NIH says supplements with thiamin are almost always recommended afterward²
You drink heavily, which cuts how much thiamin you absorb and store²
You take furosemide or another loop diuretic¹

Questions people ask

Is thiamine good for women?

Women need it for the same reason men do: to turn food into energy. Most women already get the 1.1 mg a day they need from food, so a supplement mainly matters when diet or health keeps intake low.^1,2

Is thiamine safe in pregnancy?

Thiamin is a normal part of a pregnancy diet, and the recommended amount rises to 1.4 mg a day. No upper limit is set, but ask your doctor or midwife before taking more than a prenatal vitamin provides.^1,2

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Sources

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