Most clinical trials in women have used between 90 and 180 micrograms of vitamin K2 (specifically the MK-7 form) per day, and that range is the best current basis for choosing a daily dose. No government agency has set a formal recommended daily allowance or upper limit specifically for K2, so the dosing guidance that exists comes almost entirely from intervention studies rather than official guidelines. The picture is also more nuanced than a single number, because the dose that matters depends on what you are trying to achieve and where you are in life.
Why There Is No Official Number
Vitamin K as a whole has an “Adequate Intake” set by the Institute of Medicine: 90 micrograms per day for adult women. But that number was built around vitamin K1 (phylloquinone), found in leafy greens, and was based on maintaining normal blood clotting. It was not designed with K2’s roles in bone and cardiovascular health in mind. Because no adverse effects from high vitamin K intake have been documented in healthy people, neither the IOM, the European Commission, the UK’s Expert Group on Vitamins and Minerals, nor the WHO has established a Tolerable Upper Intake Level for any form of vitamin K.1Scientific Reports. Safety evaluation of vitamin K2 (menaquinone-7) via toxicological tests That sounds reassuring, but it also means you are left without an official ceiling or target for K2 specifically.
Researchers have filled part of that gap. The doses that show up repeatedly in clinical trials on women range from 90 to 360 micrograms of MK-7 per day, with 180 micrograms being the single most commonly tested dose for bone-related outcomes.
The 180-Microgram Benchmark
The dose of 180 micrograms of MK-7 per day has the most research behind it for women. A three-year Dutch trial gave this dose to 244 healthy postmenopausal women and measured changes in bone density and bone strength.2PubMed. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women A separate dose-response study found that 180 micrograms of MK-7 reduced a key marker of vitamin K deficiency (called dp-ucMGP) by about 31% over 12 weeks, while 360 micrograms reduced it by about 46%.3PubMed. The effect of menaquinone-7 supplementation on circulating species of matrix Gla protein Both doses also improved markers of osteocalcin carboxylation, a sign that more of the body’s bone-building proteins were being activated.
The 180-microgram dose is where most supplement manufacturers have landed, partly because it sits at the inflection point in that dose-response data: you get a substantial improvement in vitamin K status, with only a modest additional gain from doubling the dose. For a woman looking for a general-purpose daily amount, 180 micrograms of MK-7 is the best-supported starting point.
Lower Doses and Bone Health
Not everyone needs 180 micrograms, and some research suggests that lower amounts still help. A randomized trial of middle-aged and elderly Chinese participants found that 90 micrograms of MK-7 per day significantly slowed bone loss at the femoral neck in postmenopausal women compared to placebo.4PubMed. Effect of Low-Dose Vitamin K2 Supplementation on Bone Mineral Density in Middle-Aged and Elderly Chinese: A Randomized Controlled Study The effect was specific to postmenopausal women; men in the same study did not show the same benefit. That 90-microgram dose is roughly what you would find in a fermented soybean dish like natto, which is one of the richest natural sources of MK-7.
The evidence on bone density, though, is not universally positive. A well-designed three-year trial of postmenopausal women with osteopenia found that MK-7 supplementation did not prevent bone density loss at the hip, femoral neck, or lumbar spine compared to placebo, and bone turnover markers were similar between groups.5PubMed. The effect of vitamin MK-7 on bone mineral density and microarchitecture in postmenopausal women with osteopenia, a 3-year randomized, placebo-controlled clinical trial A meta-analysis of randomized controlled trials found that vitamin K2 improved vertebral bone density in postmenopausal women who already had osteoporosis, but not in those without it.6PubMed. Does vitamin K2 play a role in the prevention and treatment of osteoporosis for postmenopausal women: a meta-analysis of randomized controlled trials The picture that emerges is that K2 may help more when bones are already in trouble than when they are just starting to thin.
Why MK-7 Instead of MK-4
Vitamin K2 is not a single molecule. It comes in several forms, and the two you will encounter in supplements are MK-4 and MK-7. They behave differently in the body. MK-4 has a short half-life in the blood and is cleared quickly, while longer-chain forms like MK-7 and MK-9 circulate for much longer.7PubMed Central. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women That longer half-life means MK-7 can sustain elevated blood levels on a once-daily dose, whereas MK-4 needs to be taken multiple times a day at much higher amounts (typically 15 milligrams three times daily in Japanese osteoporosis trials, a dose roughly 250 times larger than a standard MK-7 supplement).
Most of the clinical data cited throughout this article used MK-7 specifically. If you see a supplement labeled just “vitamin K2” without specifying the form, check the fine print. And if you are comparing products, make sure you are comparing the same subform, because 100 micrograms of MK-4 and 100 micrograms of MK-7 are not equivalent in terms of how long they remain active in your body.
Cardiovascular Benefits and the MGP Connection
The reason K2 gets attention beyond bone health is a protein called matrix Gla protein (MGP). MGP is one of the most potent natural inhibitors of calcification in the body. It prevents calcium from depositing in soft tissues like arterial walls. But MGP only works after it has been activated by vitamin K-dependent carboxylation.8PubMed Central. Association of the Inactive Circulating Matrix Gla Protein with Vitamin K Intake, Calcification, Mortality, and Cardiovascular Disease: A Review When vitamin K is insufficient, the inactive form of MGP accumulates, and calcium can end up in artery walls instead of bones.
Observational studies have found that higher K2 intake is associated with less coronary artery calcification and lower cardiovascular disease risk, and the mechanism is thought to run through this MGP pathway.9BMJ. Vitamin K2—a neglected player in cardiovascular health: a narrative review An adequate K2 intake activates MGP, which helps keep calcium where it belongs: in bones rather than blood vessels.10PubMed Central. Proper Calcium Use: Vitamin K2 as a Promoter of Bone and Cardiovascular Health For women who take calcium supplements for bone health, this becomes especially relevant. The concern that calcium supplementation might increase cardiovascular risk has led some researchers to argue that K2 should be a routine co-supplement whenever calcium is taken.
Pairing K2 with Vitamin D
Vitamins D and K work on overlapping parts of calcium metabolism. Vitamin D increases the production of vitamin K-dependent proteins like osteocalcin and MGP, but those proteins need K2 to become fully active through carboxylation. If you take vitamin D without enough K2, you are essentially ramping up production of proteins that cannot do their jobs properly.11PubMed Central. The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review
This synergy has been tested directly. A study of postmenopausal women with osteoporosis found that combined vitamin D3 and K2 supplementation increased lumbar spine bone density significantly more than either vitamin alone or calcium by itself.12PubMed. Effect of combined administration of vitamin D3 and vitamin K2 on bone mineral density of the lumbar spine in postmenopausal women with osteoporosis More recent surgical research echoed the finding, showing that combined K2 and D3 therapy improved bone fusion rates in osteoporotic patients undergoing spinal procedures.13Scientific Reports. Combined vitamin K2 and D3 therapy improves endoscopic fusion outcomes in osteoporotic lumbar degenerative disease: a prospective study The practical takeaway is straightforward: if you supplement with vitamin D (as many women do, especially in northern climates), adding K2 is a well-supported move.
PCOS and Metabolic Health
Some of the more intriguing recent K2 research involves polycystic ovary syndrome (PCOS), a condition affecting an estimated one in ten women of reproductive age. A randomized trial gave women with PCOS 90 micrograms of MK-7 per day for eight weeks and found significant reductions in fasting insulin, insulin resistance, triglycerides, and dihydrotestosterone (DHT) compared to placebo. The MK-7 group also saw decreases in waist circumference and body fat mass, with increases in skeletal muscle and sex hormone-binding globulin.14PubMed Central. Beneficial health effects of Menaquinone-7 on body composition, glycemic indices, lipid profile, and endocrine markers in polycystic ovary syndrome patients A follow-up from the same research group, however, found that fasting blood sugar itself was not significantly changed by eight weeks of MK-7 compared to placebo.15PubMed Central. Effect of vitamin K administration on depression status in patients with polycystic ovary syndrome: a randomized clinical trial
These results are promising but preliminary. The trials were small, and K2 is not a treatment for PCOS. Still, the metabolic improvements across multiple markers suggest that women with PCOS may be a group that benefits more than average from K2 supplementation, even at a relatively modest 90-microgram dose.
Pregnancy and Breastfeeding
Vitamin K crosses the placenta poorly, and newborns are born with low vitamin K stores. Breast milk is also relatively low in vitamin K, which is why newborns typically receive a vitamin K injection at birth. A small study found that when breastfeeding mothers supplemented with 15 milligrams of menatetrenone (MK-4) per day starting two weeks after delivery, their infants’ vitamin K status at one month was close to healthy adult levels, with much less variability than unsupplemented infants.16PubMed. Improvement of vitamin K status of breastfeeding infants with maternal supplement of vitamin K2 (MK40) That dose is far higher than what bone-health supplements contain and was used specifically to prevent vitamin K-deficient bleeding in newborns.
For pregnant and breastfeeding women, the evidence is thin and the stakes are higher. A systematic review noted that insufficient evidence exists to establish side effects from high K intake during pregnancy, but because vitamin K interacts with anticoagulant medications and crosses into breast milk, supplementation should be discussed with a healthcare provider rather than self-directed.17Scientific Reports. Vitamin K supplementation during pregnancy for improving outcomes: a systematic review and meta-analysis This is one area where the general 90–180 microgram guidance from bone health trials cannot be casually applied.
Heavy Menstrual Bleeding
Vitamin K’s classical role is in blood clotting, so it is reasonable to wonder whether K2 might help with heavy periods. A narrative review found that case reports and small observational studies suggest acquired vitamin K deficiency, from poor diet, malabsorption, or prolonged antibiotic use, can contribute to menorrhagia, and that correcting the deficiency improved bleeding in some cases.18Clinical and Experimental Obstetrics & Gynecology. The Impact of Vitamin K Deficiency on Menorrhagia: A Narrative Review The evidence here is weak, however, consisting mostly of case reports rather than controlled trials. If you have unusually heavy periods, the issue is far more likely to be hormonal, structural, or related to a clotting disorder than to a dietary K2 shortfall. Getting tested is more useful than reaching for a supplement.
Safety, Warfarin, and Who Should Be Careful
For healthy women, K2 at the doses discussed here has an excellent safety profile. As noted earlier, no upper limit has been set because adverse effects have not been demonstrated. The one major exception is women taking warfarin or other vitamin K-antagonist anticoagulants. Warfarin works by blocking vitamin K’s role in clotting, so adding K2 can directly reduce the drug’s effectiveness. Research has confirmed that even modest K2 supplementation can shift anticoagulant activity enough to matter clinically.19PubMed Central. Effect of vitamin K2 on the anticoagulant activity of warfarin during the perioperative period of catheter ablation If you are on warfarin, do not add K2 without your prescriber’s involvement. Newer anticoagulants like rivaroxaban and apixaban work through a different mechanism and are not affected by vitamin K intake in the same way.
Supplement Quality Is a Real Problem
One issue that rarely makes it into dosage conversations is whether the K2 supplement you buy actually contains what it claims. A laboratory analysis of commercially available MK-7 supplements found that the biologically active form (all-trans MK-7) was below the labeled amount in the majority of products tested. The actual content of all-trans MK-7 ranged from 5.5 to 49 micrograms per pill, and one supplement contained none at all despite the label claim. In some products, inactive cis-isomers outnumbered the active trans form by nearly four to one.20PubMed. Identification of cis/trans isomers of menaquinone-7 in food as exemplified by dietary supplements
This matters because the cis and trans configurations of MK-7 are not biologically equivalent. Research has confirmed a difference in carboxylation activity between the two forms.21PubMed Central. Carboxylative efficacy of trans and cis MK7 and comparison with other vitamin K isomers If you are choosing a supplement, look for products that specify “all-trans MK-7” and ideally carry third-party testing verification. Without that, you may be getting a fraction of what you think you paid for.
Your Gut Makes Some K2, but Probably Not Enough
Gut bacteria produce several forms of vitamin K2 (menaquinones), which has led some people to assume that supplementation is unnecessary. Research has confirmed that gut microbes can remodel dietary vitamin K precursors into bacterial menaquinones.22PubMed Central. Dietary vitamin K is remodeled by gut microbiota and influences community composition However, the K2 produced in the large intestine is mostly absorbed poorly because it is made in a part of the gut where fat-soluble vitamin absorption is limited. The contribution of gut-synthesized K2 to your overall vitamin K status is thought to be modest at best, and it is not something you can rely on as a substitute for dietary or supplemental intake.
Topical K2 for Skin
An emerging area of research involves applying MK-7 directly to the skin rather than taking it orally. A randomized, double-blind trial of women aged 35–60 tested a 0.05% MK-7 cream applied twice daily for eight weeks. The treated side showed significant improvements in wrinkle roughness on both the face and neck, along with better elasticity and reduced sagging compared to placebo.23ACS Publications. Topical Menaquinone-7 (Vitamin K2, MK-7) as a Mitochondrial Bioenergetic Activator for Skin Anti-Aging: Mechanistic Evidence in Skin Cells and a Randomized Split-Face/Neck Study The researchers attributed the effect to MK-7’s ability to activate mitochondrial energy production in skin cells. This is a single small study and very early-stage science, but it signals that K2’s relevance to women’s health may eventually extend beyond what a daily capsule addresses.
How to Know If Your K2 Status Is Low
Standard blood tests do not routinely measure vitamin K2 levels. Researchers use biomarkers like uncarboxylated osteocalcin (for bone K2 activity) and dephosphorylated-uncarboxylated MGP, or dp-ucMGP (for vascular K2 activity). The dp-ucMGP marker is increasingly being studied as a way to assess K2 status, particularly in people with chronic kidney disease, who are at high risk for both vitamin K deficiency and vascular calcification.24Journal of IMAB – Annual Proceeding (Scientific Papers). IS UNDERCARBOXYLATED MATRIX GLA PROTEIN A RELIABLE BIOMARKER OF VITAMIN K2 STATUS IN PATIENTS WITH CHRONIC KIDNEY DISEASE? These tests are not widely available outside of research settings. In practice, most women will not be able to get a precise K2 status measurement from their doctor, which is one more reason why the supplementation range from clinical trials serves as the practical guide.