Vitamin K2 is a group of fat-soluble vitamin K forms called menaquinones, most often MK-4 and MK-7. Human studies suggest it can change bone-related markers and may help maintain bone density in postmenopausal women, but findings on fractures, artery calcification, blood sugar, and other outcomes remain mixed or incomplete.
It is not a replacement for prescribed medicine. The most important practical point is that vitamin K can interact seriously with warfarin and similar anticoagulants.
Vitamin K2 quick facts
| Question | What human research reports |
|---|---|
| Forms | Vitamin K2 includes menaquinones. MK-4, MK-7, and MK-9 are among the most studied forms. |
| Doses reported | Japan uses 45 mg of MK-4 as a pharmacological osteoporosis treatment. An MK-7 meta-analysis reported subgroup findings for doses at or below 90 mg. |
| Study length | Bone reviews included long-term follow-up studies. A cancer meta-analysis reported outcomes at one, two, and three years. |
| Main studied uses | Bone density and bone-turnover markers; fracture outcomes; arterial calcification; metabolic markers; and outcomes in people receiving treatment for liver cancer. |
MK means menaquinone, followed by a number that identifies the form. The NIH vitamin K fact sheet notes that MK-7 has a longer half-life than vitamin K1 in one absorption study.
What do human studies show?
Bone density and fracture outcomes
The strongest body of evidence is in postmenopausal women. A 2022 systematic review and meta-analysis of randomized controlled trials pooled 16 trials with 6,425 participants. It found a statistically significant improvement in lumbar-spine bone mineral density. Across six trials, however, there was no significant difference in fractures overall. After one heterogeneous study was removed, the pooled fracture result favored vitamin K2. That shift means the fracture finding needs careful interpretation rather than being treated as settled.
A second review (J Bone Miner Metab, 2022) included nine randomized trials with 6,853 participants and reported higher percentage changes in lumbar and forearm bone mineral density with vitamin K2. It also reported more adverse reactions overall in the vitamin K2 group, although no serious adverse events were attributed to supplementation.
For a comparison of how evidence questions can differ across vitamin forms and study designs, see the site’s vitamin d3 d2 bone health guide.
Bone-turnover markers
A systematic review and meta-analysis summarized on PubMed included nine randomized trials with 2,570 postmenopausal osteoporosis participants. Vitamin K2 increased osteocalcin and bone-specific alkaline phosphatase and reduced undercarboxylated osteocalcin and tartrate-resistant acid phosphatase. CTX, another bone-turnover marker, fell by a small amount with uncertain clinical importance, while NTX did not change significantly.
These are marker changes, not the same thing as fewer fractures or a treatment outcome. That distinction matters when reading a supplement label or ad.
Artery calcification and heart outcomes
Vitamin K has been studied because arterial calcification can reduce artery elasticity. The NIH fact sheet describes a three-year trial in which participants received 500 mcg daily of vitamin K1 alongside a multivitamin, vitamin D3, and calcium. The overall group had no significant difference in coronary artery calcification versus the comparison group. Among participants who followed the protocol, and among those with calcification at the start, results differed, but the study authors called for larger studies.
That trial studied vitamin K1 rather than K2. The NIH Office of Dietary Supplements says the role of different vitamin K forms in arterial calcification and coronary heart disease remains unclear.
Blood sugar, insulin, and cholesterol markers
A systematic review and meta-analysis of six original MK-7 studies found favorable pooled results for insulin-related measures, HbA1c, and total cholesterol, but heterogeneity was high for several outcomes. Its subgroup analysis found negligible effects on several measures among people receiving 90 mg or less of MK-7 for under 12 weeks. The authors called for higher-quality original research before drawing a consistent conclusion.
Outcomes during liver-cancer treatment
A 2026 meta-analysis included 11 studies and 1,030 people receiving treatment for hepatocellular carcinoma. It reported lower recurrence and mortality odds at one, two, and three years with vitamin K supplementation than with control groups. The abstract also says the potential benefits remain unclear and reports a very wide confidence interval for adverse events. This is a specific treatment population, not evidence that vitamin K2 should replace cancer care or apply to people without that condition.
What doses have researchers used?
These are study or treatment-context doses, not a recommendation for you. The NIH fact sheet reports that 45 mg of MK-4 is used pharmacologically for osteoporosis in Japan. The MK-7 meta-analysis described subgroup results at 90 mg or less for less than 12 weeks. The bone-density reviews pooled trials with different regimens, so they do not provide one single research dose that fits every study.
Study dose is only one part of the result. Population, form, comparison group, length, and outcome all matter. The vitamin d clinical research landscape explains why a dose from one trial should not be read as a universal instruction.
Safety, side effects, and medicine interactions
The NIH fact sheet says the Food and Nutrition Board did not set an upper intake level for vitamin K because of its low potential for toxicity, and it reports that adverse effects from vitamin K in food or supplements have not been reported in humans or animals. That general statement does not remove the need to account for medicine interactions.
| Medicine or situation | Why it matters |
|---|---|
| Warfarin and similar anticoagulants | Vitamin K can have a serious and potentially dangerous interaction. |
| Bile acid sequestrants, including cholestyramine and colestipol | These medicines can reduce absorption of vitamin K and other fat-soluble vitamins. |
| Orlistat | It can reduce absorption of fat-soluble vitamins, including vitamin K. Combining orlistat with warfarin may significantly increase prothrombin time. |
The interaction details come from the NIH vitamin K fact sheet. If you take a prescription medicine regularly, your clinician or pharmacist can help you assess an ingredient and dose without changing your medicine on your own.
Who should talk to a clinician first?
Talk to a clinician or pharmacist before using a vitamin K2 supplement if you take warfarin or a similar anticoagulant. The same step is sensible if you use a bile acid sequestrant or orlistat, because those medicines can affect vitamin K absorption or management. The NIH says people taking warfarin and similar anticoagulants need to keep their vitamin K intake consistent, because sudden changes can raise or lower the anticoagulant effect.
What is still unknown?
Vitamin K2 research does not yet give one clear answer for every outcome. Fracture results changed when one heterogeneous study was excluded from a meta-analysis. Arterial-calcification research remains unsettled, and metabolic findings need better original studies. Bone-marker changes are measurable, but longer-term clinical outcomes remain the key question.
How to read a vitamin K2 label
Start with the amount per serving and the form. Look for whether the label identifies MK-4 or MK-7, because these are different menaquinones and both appear in research. The NIH says supplements may contain vitamin K2 as MK-4 or MK-7 and that doses vary widely, with some vitamin K supplements providing very high amounts.
- Check the amount per serving, not just the front-label claim.
- Check whether the form is stated as MK-4 or MK-7.
- If a proprietary blend appears, ask the manufacturer for the exact vitamin K2 form and amount before deciding.
- If you use an anticoagulant or another relevant medicine, bring the complete label to your clinician or pharmacist.
For another example of separating a nutrient’s form, dose, and human outcomes, see vitamin e benefits evidence.
By ClinicalStudyConnect.com Research Desk