Key Takeaway
Nutricost Vitamin K2 (MK-4) is a single-active product: 100 micrograms of vitamin K2 as menatetrenone (MK-4) per capsule, 240 capsules per bottle, one capsule a day. At $14.95 that is about 6 cents per capsule. The research is the honest problem. The fracture-prevention trials that used menatetrenone gave 45 milligrams a day, 450 times the dose in this capsule. The trials that used a supplement-sized dose mostly used MK-7, a different form. A human bioavailability study found that small doses of MK-4 did not raise serum MK-4 at all, although MK-7 did. Meta-analyses of vascular calcification are encouraging on a surrogate marker but small and inconsistent, and the bone meta-analysis found no clear effect on bone density. Anyone taking warfarin must not add vitamin K without their prescriber. This review is built on the listing and the published literature.
Vitamin K2 is one of those supplements with a great origin story and a murkier evidence file. The story is tidy: vitamin K activates proteins that handle calcium, so it should help put calcium into bone and keep it out of arteries. Every part of that is biologically plausible. The problem is that the human trials do not line up as neatly as the story, and the product you are standing in front of makes the mismatch worse, because the form on this label is not the form used in most of the supplement-dose research.
This review looks at one specific product, Nutricost Vitamin K2 as MK-4. We cover what the retailer listing states, why the choice of MK-4 over MK-7 matters, what the bone and vascular trials show at realistic doses, how the warfarin interaction works, and what a capsule costs. It is a research review, not a claim that we have used the product and measured something. We already cover the underlying biology in our vitamin K2 (MK-4) guide, so this article stays on the product and the evidence quality rather than repeating the mechanism.
What You Are Buying
The details below come from the Amazon listing for Nutricost Vitamin K2 (MK-4), 240 capsules, 100 mcg. The supplement facts panel is an image on some listings, so serving information here comes from the listing's text bullets and its ingredient and directions fields. Check the bottle you receive against it.
| Label Detail | What the Listing States |
|---|---|
| Active ingredient | Vitamin K2 as menatetrenone (MK-4), listed as the only active ingredient |
| Amount per serving | 100 mcg of vitamin K2 per capsule |
| Serving size | 1 capsule |
| Servings per container | 240 |
| Other ingredients | Rice flour, hypromellose (cellulose) capsule, dextrin |
| Directions | 1 capsule daily with 8 to 12 oz of water, or as directed by a healthcare professional |
| Claims | Non-GMO, gluten free; made in an NSF-certified, GMP-compliant, FDA-registered facility |
| Listed price | $14.95 for 240 capsules |
Three things stand out. First, the product is a single active at a low dose, 100 mcg, which is a nutritional-scale amount rather than a drug-scale one. Second, the listing says "For healthy individuals 18 years and older" and asks anyone taking medication to talk to a healthcare professional first, which, as you will see, is not boilerplate here. Third, the facility claim is about the factory, not the product, and we address that in the quality section.
MK-4 vs. MK-7: Why the Form Matters
Vitamin K is a family of compounds. Phylloquinone, vitamin K1, comes mainly from leafy greens and plant oils. The menaquinones, vitamin K2, are named MK-4 through MK-13 by the length of a side chain. According to the NIH Office of Dietary Supplements, menaquinones are found in some fermented foods and in modest amounts in meat, dairy, and eggs. In the supplement aisle you will mostly see two K2 forms. MK-4 is the short-chain form, and MK-7 is a longer-chain form; the MK-7 used in the Norwegian trial below came from natto, the fermented soybean food.
The two are not equivalent in the body, and the best human data on that point cuts against MK-4 supplements at small doses. Sato, Schurgers, and Uenishi (2012) compared the two forms in healthy Japanese women. In the single-dose arm, 420 micrograms of MK-4 or 420 micrograms of MK-7 was taken with a standardized breakfast. MK-7 was well absorbed, peaked in serum at about 6 hours, and was still detectable 48 hours later. MK-4 was not detectable in the serum of any subject at any time point. In the consecutive-dose arm, 60 micrograms a day of each form for seven days, MK-4 did not raise serum MK-4 levels, while MK-7 raised serum MK-7 significantly in all subjects. The authors concluded that MK-4 at nutritional doses does not contribute to vitamin K status as measured in serum, whereas MK-7 may be of particular importance for tissues outside the liver.
That result deserves a fair reading, not an overreading. It is one small study, in women, over a short period, and it measured blood levels. MK-4 may be taken up by tissues quickly and may act there without lingering in the blood, and a serum assay cannot settle that. The honest takeaway is narrower: if you are buying vitamin K2 to raise circulating K2, the only controlled comparison we found favors MK-7, and this capsule is MK-4. It does not prove the capsule does nothing.
The Dose Problem: 100 mcg vs. What the Trials Used
For vitamin K overall, the Adequate Intake listed by the NIH Office of Dietary Supplements is 120 mcg a day for men and 90 mcg for women aged 19 and older. These numbers describe total vitamin K intake, mostly phylloquinone from food. A 100 mcg capsule is in the same range as that figure, but it is a different compound doing a different job in the diet, and the AI was not set to describe MK-4 specifically.
Now compare with the trial doses. The best-known MK-4 fracture trial is Shiraki and colleagues (2000), a 24-month randomized, open-label study of 241 Japanese patients with osteoporosis. The treated group received 45 mg a day of menatetrenone, which is 45,000 mcg, or 450 capsules of this product's strength. The authors reported fewer new clinical fractures in the treated group and a smaller loss of lumbar bone density (about 0.5 percent loss at 24 months versus 3.3 percent in controls), and the abstract itself notes that the treated group did not gain lumbar bone density. The study was open label, so neither the participants nor the investigators were blinded. The relevance to a 100 mcg capsule is limited: a result at 450 times the dose does not transfer to the small one.
The supplement-sized trials mostly used MK-7. Emaus and colleagues (2010) randomized 334 healthy Norwegian women, 1 to 5 years past menopause, to 360 mcg of MK-7 as natto capsules or placebo for a year. Bone loss rates at the total hip and every other site did not differ between groups, even though a marker of undercarboxylated osteocalcin fell, which shows the vitamin was biologically active. Rønn and colleagues (2016) gave 375 mcg of MK-7 for 12 months to 148 postmenopausal women with osteopenia, all of whom also received calcium and vitamin D. Bone mineral density did not differ between groups, but high-resolution imaging at the tibia showed that trabecular architecture was preserved in the MK-7 group while the placebo group showed age-related deterioration. That is an interesting finding and a secondary one, in a single trial.
So there is a gap on both sides. The dose that moved fractures was a drug-level dose of MK-4. The dose in the capsule is a nutritional one, and the nutritional-dose trials used the other form. Nobody should buy this product and assume the fracture data applies to it.
What the Reviews Say About Bone and Arteries
Bone
Mott and colleagues (2019) updated a systematic review of randomized trials of oral vitamin K for bone mineral density and fractures, now covering 36 studies. For post-menopausal or osteoporotic patients, the odds of any clinical fracture were lower with vitamin K (odds ratio 0.72, 95% CI 0.55 to 0.95). Restricting to low-risk-of-bias trials, the odds ratio was 0.76 (95% CI 0.58 to 1.01), which no longer clears statistical significance. Vertebral fractures showed no difference (OR 0.96, 95% CI 0.83 to 1.11). Lumbar spine bone density change was higher at two years (mean difference 1.63 percent, 95% CI 0.10 to 3.16), but removing high-risk-of-bias trials tended to shrink the difference to non-significance. The authors concluded that there is no evidence vitamin K affects bone density or vertebral fractures in these patients, that it may reduce clinical fractures, and that the evidence is insufficient to confirm even that. They also noted that there are too few trials to say anything about other groups, which includes healthy male lifters.
That is the realistic bone picture: a possible, unconfirmed signal for fractures in older and osteoporotic populations, much of it from the high-dose Japanese MK-4 literature, and no demonstrated effect on bone density.
Vascular calcification
Lees and colleagues (2019) pooled 13 controlled trials with 2,162 participants on vitamin K supplementation and vascular health, in the journal Heart. Supplementation was associated with a significant reduction in vascular calcification (-9.1 percent, 95% CI -17.7 to -0.5, p = 0.04) and large drops in inactive vitamin K-dependent proteins, such as dephospho-uncarboxylated matrix Gla protein (-44.7 percent). Vascular stiffness did not improve significantly. The authors flagged substantial heterogeneity and small numbers of studies and called for larger trials. The interesting part is the gap between the biochemical markers and anything a person would feel or an event a cardiologist would count. These are surrogate endpoints. A trial that shows less calcification on a scan is not the same as a trial that shows fewer heart attacks, and that second trial has not been done at scale.
The sensible reading for a lifter in their 20s to 40s is that vitamin K status matters, adequate intake is a good idea, and there is a hypothesis that higher K2 intake might help in older people with vascular risk. None of this establishes that a 100 mcg MK-4 capsule changes anything you can measure at your age.
What the Evidence Is Really Saying
The strongest effect in the literature is biochemical: vitamin K supplements reliably lower the inactive forms of vitamin K-dependent proteins. The step from that marker to stronger bones or cleaner arteries is where the evidence thins out, and the specific form and dose in this capsule were not the ones tested for the strongest claims.
Food First, and Where Observational Data Fits
Before spending on a capsule, it is worth knowing where vitamin K comes from. The Office of Dietary Supplements lists vegetables, especially green leafy ones, vegetable oils, and certain fruits as good sources of phylloquinone, and notes that menaquinones turn up in some fermented foods and in modest amounts in meat, dairy, and eggs. It also says that the phylloquinone in plant foods is less bioavailable than the phylloquinone in oils or supplements. In other words, a lifter who eats a daily salad with an oil-based dressing, eggs, and some dairy is probably not starting from zero, and the capsule is topping up a diet that already contributes.
The same fact sheet cites a Dutch cohort of 4,807 men and women aged 55 and older. People in the middle tertile of dietary menaquinone intake (21.6 to 32.7 mcg a day) and the upper tertile (more than 32.7 mcg a day) had a 27 percent and 57 percent lower risk of coronary heart disease mortality, respectively, than the lowest tertile, while phylloquinone intake had no effect on any outcome. That is a striking pattern, and it is the source of a lot of K2 marketing. It is also observational. People who eat more menaquinone-rich fermented foods and dairy differ from other people in many ways, and food intake is not the same thing as a 100 mcg MK-4 capsule. The fact sheet itself notes that few trials have tested vitamin K supplements for these outcomes, which is precisely the gap this review keeps running into.
One more practical note for anyone on a stable anticoagulant plan: a supplement you take on some days and skip on others is a worse fit than one you take every day, since the guidance is about consistency. If you are on warfarin, that consistency is for your prescriber to set, not for a supplement label.
What It Costs Per Day and Per Year
The price math is the strongest argument for this product. At $14.95 for 240 capsules, each capsule costs about 6.2 cents.
| Use Pattern | Capsules Per Day | Cost Per Day | Days Per Bottle |
|---|---|---|---|
| Label directions | 1 | about $0.06 | 240 |
| Cost for one full year (365 days) | 1 | about $22.74 per year | 1.5 bottles |
For a year of daily use, you would spend about $23, which is cheap. That also means the financial risk is low and the real question is whether to take it at all. We have not fetched prices for competing products, so we make no price comparison. If you are comparing, check the amount, the form (MK-4 vs. MK-7), and the serving size on each label, because a lower price per capsule can hide a smaller dose or a different form.
Safety and the Warfarin Interaction
The NIH Office of Dietary Supplements states that vitamin K does not have a Tolerable Upper Intake Level because it has a low potential for toxicity, and it quotes the Food and Nutrition Board as saying that no adverse effects of vitamin K from food or supplements have been reported in humans or animals. That is reassuring for most healthy adults. It is also not the whole story, because of one interaction that matters a great deal.
Warfarin (Coumadin) and similar anticoagulants work by antagonizing vitamin K. The Office of Dietary Supplements says people taking them need to maintain a consistent intake of vitamin K from food and supplements, because sudden changes can raise or lower the anticoagulant effect. That means starting a vitamin K capsule is a medically relevant change for anyone on warfarin, even at 100 mcg. It also means stopping it is.
A Cochrane review by Mahtani and colleagues (2014) looked at the opposite idea, whether a low daily dose of vitamin K could help stabilize control in people on warfarin. It found only two trials with 100 participants and unclear risk of bias. In the larger one, 150 mcg of oral vitamin K improved anticoagulation control in people with unexplained instability, while the second, with 30 participants and available only as an abstract, found no significant improvement at 175 mcg. The takeaway is not that anyone should self-dose. It is that this is a prescriber-managed question and a poor place to experiment.
When to Talk to Your Doctor First
If you take warfarin or another anticoagulant, do not start or stop vitamin K2 without your prescriber. Also ask first if you are pregnant or nursing, take other medications, or have a medical condition, which is consistent with the cautions on the listing. This article is research summary, not medical advice.
Quality and Third-Party Testing
The listing says the product is made in an NSF-certified, GMP-compliant, FDA-registered facility and, in the safety text, says not to use it if the safety seal is broken or missing. The retrieved bullets did not say this specific product carries a product-level third-party certification such as a public NSF Certified for Sport listing. Facility certification describes how a plant operates. It does not guarantee that a particular lot contains 100 mcg of MK-4. If testing matters to you, for example because you compete in tested sport, check the bottle and the company's site, and ask for a certificate of analysis for your lot.
Who Should Buy It and Who Should Skip It
It may make sense if your diet is low in leafy greens, fermented foods, and the animal foods that contain menaquinones, you want an inexpensive low-dose K2 and are comfortable that the evidence is thin, and you are not on an anticoagulant. At about 6 cents a day the cost is easy to justify as a low-stakes experiment.
Skip it, or choose differently, if you take warfarin or a similar drug, you specifically want the form with the human serum-level data, which is MK-7, or you expect this capsule to build bone or clear plaque. In that case you would be buying a hope. Also remember the larger hierarchy: heavy lifting, adequate protein, calcium and vitamin D status, and sleep do much more for bone than any single vitamin. Our vitamin D3 guide covers the nutrient that is usually paired with K2 in the bone literature, and our multivitamin guide looks at what a general product might already provide.
How HonestLifter Is Reviewing This Product
This is a research review built on the manufacturer's listing and the published studies. HonestLifter's plan for each product is a written review first, then dated checkpoint updates at 30, 60, 90 days, 6 months, and 12 months, backed by our own notes and data and added to this page as they are written. The program is described in our longitudinal review program post.
| Checkpoint | Timing | Status |
|---|---|---|
| 30 day | 30 days of use | Combined note published |
| 60 day | 60 days of use | Combined note published |
| 90 day | 90 days of use | Combined note published |
| 6 month | 6 months of use | Combined note published |
| 12 month | 12 months of use | Not yet |
Checkpoint Update: 30-Day, 60-Day, 90-Day and 6-Month Notes (October 2026)
HonestLifter's owner reports the following from regular use. These are personal notes, not measurements.
- Use: Daily, in the morning with other morning supplements.
- Effect: No effect that can be attributed to it. Because it is taken alongside other supplements, one product's effect would be hard to isolate anyway.
- Verdict: Would buy again.
Several supplements are taken together, so none of these notes isolates the effect of this product. The 12-month update will be added when it is written.
The Bottom Line
Nutricost Vitamin K2 (MK-4) delivers exactly what the label says: one active ingredient, a nutritional-scale dose, a low price, and a year of supply for about $23. What it cannot do is borrow credibility from trials it did not replicate. The fracture trial used 450 times the dose. The supplement-dose bone trials used MK-7. The one human bioavailability comparison found MK-4 at small doses did not raise serum MK-4. The calcification meta-analysis found a modest reduction in a surrogate marker, with the authors warning about heterogeneity.
Buy it if you want a cheap, low-risk K2 and understand that the evidence is thin. If form matters to you, consider the MK-7 route and read that label as carefully. If you take warfarin, talk to your prescriber before anything changes. Watch this page for dated checkpoint updates from the editor's own notes.
References
- Sato, T., Schurgers, L.J., & Uenishi, K. (2012). Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutrition Journal, 11, 93. doi:10.1186/1475-2891-11-93. PMID 23140417.
- Mott, A., Bradley, T., Wright, K., Cockayne, E.S., Shearer, M.J., Adamson, J., Lanham-New, S.A., & Torgerson, D.J. (2019). Effect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials. Osteoporosis International, 30(8), 1543-1559. doi:10.1007/s00198-019-04949-0. PMID 31076817.
- Emaus, N., Gjesdal, C.G., Almas, B., Christensen, M., Grimsgaard, A.S., Berntsen, G.K., Salomonsen, L., & Fonnebo, V. (2010). Vitamin K2 supplementation does not influence bone loss in early menopausal women: a randomised double-blind placebo-controlled trial. Osteoporosis International, 21(10), 1731-1740. doi:10.1007/s00198-009-1126-4. PMID 19937427.
- Ronn, S.H., Harslof, T., Pedersen, S.B., & Langdahl, B.L. (2016). Vitamin K2 (menaquinone-7) prevents age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women. European Journal of Endocrinology, 175(6), 541-549. doi:10.1530/EJE-16-0498. PMID 27625301.
- Shiraki, M., Shiraki, Y., Aoki, C., & Miura, M. (2000). Vitamin K2 (menatetrenone) effectively prevents fractures and sustains lumbar bone mineral density in osteoporosis. Journal of Bone and Mineral Research, 15(3), 515-521. doi:10.1359/jbmr.2000.15.3.515. PMID 10750566.
- Lees, J.S., Chapman, F.A., Witham, M.D., Jardine, A.G., & Mark, P.B. (2019). Vitamin K status, supplementation and vascular disease: a systematic review and meta-analysis. Heart, 105(12), 938-945. doi:10.1136/heartjnl-2018-313955. PMID 30514729.
- Mahtani, K.R., Heneghan, C.J., Nunan, D., & Roberts, N.W. (2014). Vitamin K for improved anticoagulation control in patients receiving warfarin. Cochrane Database of Systematic Reviews, 2014(5), CD009917. doi:10.1002/14651858.CD009917.pub2. PMID 24832594.
- National Institutes of Health, Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/.
Product details were taken from the manufacturer's Amazon listing and may change. HonestLifter carries no affiliate links. This article is educational and is not medical advice.