Quick answer

Women need 30 mcg of biotin a day, the same as men, and 35 mcg while breastfeeding. Biotin is marketed to women for hair and nails, but the studies are small and had no placebo group. It can also throw off thyroid and other hormone blood tests.^1,2,3

Key facts

Prenatal vitamins often contain biotin, as do many multivitamins and hair, skin and nail products.²
At least a third of pregnant women develop marginally low biotin status even with normal intakes.¹
One nail study gave 2.5 mg a day for 6 to 15 months to 22 women with brittle, splitting or soft nails.¹
Laboratory reviews list reproductive hormone tests among those biotin can upset.^3,4

How much biotin women need

Biotin for girls and women, adequate intake per day^5,6
Life stage	Biotin per day
Girls 14 to 18	25 mcg
Women 19 and older	30 mcg
Pregnant teens and women	30 mcg
Breastfeeding teens and women	35 mcg

Age does not change the figure after 19. Women over 40, over 50 and over 60 have the same 30 mcg target, and a mixed diet usually covers it.¹

Pregnancy and breastfeeding

At least a third of pregnant women develop marginally low biotin status despite normal intakes, and biotin in blood and breast milk falls during breastfeeding even when intake is above the adequate intake. What this means for health is not yet known.¹

NIH lists pregnant and breastfeeding women among the groups more likely to have trouble getting enough biotin. Because prenatal vitamins often already contain it, check that label before adding a separate biotin product.^2,5

Hair and nails: what the studies in women found

Much of the nail research involved women. One study of 2.5 mg a day for 6 to 15 months included 22 women with brittle, splitting or soft nails and 10 healthy volunteers. Nails were 25% thicker in the 8 people whose samples were taken just before and after, but only 7% thicker, a change that was not statistically significant, in 14 people sampled later.¹

None of the three nail studies had a placebo group or checked whether the women were low in biotin at the start, so they cannot show that biotin caused the change.¹

For hair, our sources contain no trial of biotin in women who were not short of it. A review of 18 published cases found that everyone whose hair or nails changed on biotin had an underlying cause for poor growth.⁷

NIH says more research is needed to know whether biotin supplements make any difference to hair, nails or skin, especially in healthy people.^1,5

Thyroid, hormone and pregnancy tests

The tests most at risk include thyroid and reproductive hormone tests, heart tests such as troponin, and tests that measure some immune-suppressing medicines. Since 2016, 92 cases of suspected biotin interference have been reported to FDA.³

One laboratory review lists estradiol, progesterone, testosterone, LH and FSH among the hormone tests biotin can affect, and describes beta hCG tests, used to confirm pregnancy, as robust.⁴

Case reports describe thyroid test results that falsely suggested Graves' disease or a severely overactive thyroid in people taking 10 to 300 mg of biotin a day.¹

If you are having thyroid or reproductive hormone tests, tell the clinic and the lab that you take biotin, and ask whether to pause it first and for how long. Results that do not match how you feel are worth raising with your doctor.¹

Who should ask first

Women who are pregnant or breastfeeding, before adding biotin to a prenatal vitamin
Women who take levothyroxine or another thyroid medicine⁸
Women who take an anticonvulsant such as carbamazepine or phenytoin, which can lower biotin¹
Anyone with blood tests coming up

Questions people ask

Does biotin help hair growth in women?

There is no good evidence that it does unless a woman is short of biotin, which is rare. NIH says the hair claims rest on case reports in children, and a review of the published cases found too little evidence to recommend biotin to people without an underlying cause.^1,7

Can biotin affect a pregnancy test?

One laboratory review describes beta hCG tests, the kind used to confirm pregnancy, as robust to biotin. Tests differ by maker, though, so tell the clinic or lab that you take biotin.^4,9

Can I take biotin while pregnant?

Pregnant women need 30 mcg a day, and prenatal vitamins often supply it. Ask your doctor or midwife before taking a separate biotin supplement, and tell them about it before any blood tests.^1,2

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Sources

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