Quick answer
Women need 90 mcg of vitamin K a day, the same in pregnancy and while breastfeeding, and US women average 122 mcg from food. Most vitamin K bone trials studied women after menopause: one 3-year trial of 180 mcg of MK-7 a day reported a slower decline in bone density, but pooled trials are mixed.1,2,3,4
Key facts
- Pregnant and breastfeeding teens need 75 mcg of vitamin K a day.1
- Newborns get a vitamin K shot at birth, because little crosses the placenta and breast milk is low in it.2
- With supplements counted, US women average 164 mcg of vitamin K a day.2
- No upper limit has been set for vitamin K at any age.2
How much women need
| Stage | Adequate intake |
|---|---|
| Girls 14 to 18 | 75 mcg |
| Women 19 and older | 90 mcg |
| Pregnant or breastfeeding, aged 14 to 18 | 75 mcg |
| Pregnant or breastfeeding, aged 19 and older | 90 mcg |
The figure is the same for every adult woman, and it covers K1 and K2 together. Women in the US already average 122 mcg a day from food, above that mark, so a true shortfall is uncommon.2
After menopause: what the bone trials found
Most trials of vitamin K and bone have been in women after menopause, when bone density tends to fall. The results depend heavily on the form, the dose and the trial, and the grades below reflect that.4,5
MK-7 may help maintain bone mineral density in women after menopause*2,3,4
Early evidence
One three-year randomized trial in 244 healthy women after menopause found that 180 mcg of MK-7 a day slowed the usual decline in bone mineral content and density at the lower spine and the femoral neck, though not at the total hip, and bone strength measures held up better than on placebo. It came from a single vitamin K research group, and other trials of vitamin K have found no effect on bone density, so the evidence is early.
Amount studied: 180 mcg of MK-7 a day for three years
Contributes to the maintenance of normal bones*2,4
Moderate evidence
Vitamin K is needed to activate osteocalcin, a protein in bone, and NIH reports that the European Food Safety Authority found a cause and effect relationship between dietary vitamin K and the maintenance of normal bone. Supplements beyond a normal intake are another matter: trials are mixed, a 2019 review of 36 randomized trials found no clear effect on bone mineral density in women after menopause once lower quality trials were set aside, and the FDA has not authorized a health claim for vitamin K in the US.
Amount studied: Adequate intake of 90 to 120 mcg a day from food; supplement trials used from 180 mcg of MK-7 to 45 mg of MK-4 a day
In a 12-month trial of 381 women after menopause, 1 mg of K1 or 45 mg of MK-4 a day activated more osteocalcin than placebo but made no difference to bone mineral density at the spine or hip. Every woman in the trial also took calcium and 400 IU of vitamin D3.2
When vitamin D or calcium is given alongside vitamin K in a trial, it can be hard to tell which nutrient made any difference to bone, which may explain some of the mixed results.2
Pregnancy, breastfeeding and newborns
Little vitamin K crosses the placenta and breast milk is low in it, so newborns have little at birth. The American Academy of Pediatrics recommends a single shot of 0.5 to 1 mg of vitamin K1 for every newborn.2
For adult women the amount stays at 90 mcg a day through pregnancy and breastfeeding. Because so little vitamin K crosses the placenta, newborns rely on the shot given at birth.1,2
K2 with D3 for women
Vitamin K is often sold in one product with calcium, magnesium or vitamin D. There is no official K2 to D3 ratio. A woman's vitamin D need, 15 mcg (600 IU) a day until 70, is set on its own, and our vitamin D guide for women covers it.1,2,6
Cautions
Ask your pharmacist or doctor first
Warfarin and similar blood thinners work by blocking vitamin K. A sudden rise in vitamin K from food or supplements can weaken their effect and raise the chance of a blood clot, and a sudden drop can strengthen it and cause dangerous bleeding. NIH and the warfarin label advise keeping vitamin K intake about the same from day to day. NIH names warfarin and similar medicines used in Europe (phenprocoumon, acenocoumarol and tioclomarol), not blood thinners that work in other ways.1,2,7,8
On the medicine's label
- Ask your doctor or midwife before taking a vitamin K supplement while pregnant or breastfeeding
- Ask first if you have had a blood clot, or have a bleeding or clotting disorder
- Ask first if you take orlistat, a bile acid sequestrant such as cholestyramine, or a long course of antibiotics1
Questions people ask
Is vitamin K2 good for women over 50?
Possibly, but the evidence is early. One 3-year trial in healthy women after menopause found that 180 mcg of MK-7 a day slowed the usual decline in bone density, while a pooled analysis of 36 trials found no clear effect once lower quality trials were set aside. Reaching 90 mcg of vitamin K a day from all sources is the firm part.1,3,4
Do women need more vitamin K than men?
No, a little less: 90 mcg a day for women against 120 mcg for men.1
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Sources
- Office of Dietary Supplements, National Institutes of Health. Vitamin K: Fact Sheet for Consumers. Updated March 22, 2021. Opened 2026-10-07.
- National Institutes of Health, Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. Updated March 29, 2021. Opened 2026-10-07.
- Knapen MH, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499-2507. Opened 2026-10-07.
- Mott A, et al. Effect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials. Osteoporos Int. 2019;30(8):1543-1559. Correction: Osteoporos Int. 2020;31(11):2269-2270. Opened 2026-10-07.
- National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. Updated June 27, 2025. Opened 2026-10-07.
- Office of Dietary Supplements, National Institutes of Health. Vitamin D: Fact Sheet for Consumers. Updated November 8, 2022. Opened 2026-10-07.
- Warfarin sodium tablets: prescribing information (Amneal Pharmaceuticals). DailyMed, U.S. National Library of Medicine. Published June 3, 2026. Opened 2026-10-07.
- Warfarin. MedlinePlus Drug Information, U.S. National Library of Medicine. Last revised March 15, 2026. 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.