Health Reference LibraryVitamin K2 (MK-7): what it does and who must not take it
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
MK-7 is the long-acting form of vitamin K2, with a half-life of around three days against hours for vitamin K1, which is why a single daily capsule maintains steady activity. Vitamin K activates osteocalcin, which binds calcium into the bone matrix, and matrix Gla protein, which research suggests may help limit calcium deposits in soft tissue, though the artery evidence is mainly observational while the bone evidence includes a three-year randomised trial of 180mcg MK-7 in postmenopausal women. No upper intake level exists because harm has not been shown at supplemental doses. The line that cannot be crossed is warfarin: anyone on warfarin or a similar anticoagulant must not start K2 without their anticoagulant clinic's agreement.
How it works
Vitamin K is the cofactor for the carboxylase enzyme that activates a family of proteins. Two matter most here. Osteocalcin, made in bone, needs vitamin K activation before osteocalcin can bind calcium into the bone matrix. Matrix Gla protein, present in vascular smooth muscle, is the body's local brake on abnormal calcification, and matrix Gla protein also requires vitamin K activation. Menaquinones such as MK-7 circulate longer than K1, which in principle leaves more vitamin K available to tissues beyond the liver's clotting factories.
Effective dose
The US adequate intake for vitamin K overall is 120mcg daily for men and 90mcg for women, and UK guidance frames the need as roughly 1mcg per kilogram of body weight per day, figures normal diets usually meet through K1 in greens. Supplemental MK-7 studies have typically used 90 to 180mcg daily, and the trial with the strongest bone outcome used 180mcg for three years. This capsule provides 150mcg of MK-7, sitting inside that studied range, and one capsule daily is the complete dose.
Forms compared
Each capsule provides 150mcg of vitamin K2 as menaquinone-7 in a vegetarian capsule shell, made in the UK. MK-7 has a half-life of around three days, far longer than MK-4 or K1, so once-daily dosing holds steady blood levels. Vitamin K is fat soluble, so a capsule taken with a meal containing some fat absorbs better than one taken on an empty stomach. Food sources of MK-7 are narrow, with natto the standout and fermented cheeses contributing smaller amounts.
Timing
Take MK-7 with a meal that contains some fat, since vitamin K is fat soluble and absorbs with dietary lipids. Many people pair K2 with vitamin D3 at the same meal, a sensible habit given the two are often supplemented together and both are fat soluble. The long half-life means a missed day matters little; consistency across the week matters more than clock time.
Safety profile
No tolerable upper intake level has been set for vitamin K because no adverse effects from food or supplements have been reported in the studies reviewed, per the NIH Office of Dietary Supplements. The serious risk is entirely about anticoagulants. Warfarin works by antagonising vitamin K, so adding or stopping a K2 supplement changes the drug's effect and can swing INR dangerously. Anyone on warfarin, phenprocoumon or acenocoumarol must involve their anticoagulant clinic before any change in vitamin K intake, including starting this capsule. The newer direct anticoagulants (apixaban, rivaroxaban, dabigatran) do not work through vitamin K, but any anticoagulated person should still confirm with their prescriber.
Special populations
People taking warfarin are the population for whom this supplement is a genuine hazard without their prescriber's oversight, and consistency of vitamin K intake is the principle their clinics work to. People with malabsorption conditions, on long-term antibiotics, on bile acid sequestrants or on orlistat absorb or retain less vitamin K and may reasonably discuss status with a clinician. Pregnancy and breastfeeding intakes at ordinary supplemental levels are considered within normal ranges, but high-dose combinations deserve a midwife or GP conversation.
Interactions
Warfarin and similar vitamin K antagonists are the defining interaction, serious and dose-dependent in both directions. Antibiotics can reduce gut bacterial vitamin K production over prolonged courses. Bile acid sequestrants and orlistat reduce fat-soluble vitamin absorption, vitamin K included. Nutri365 checks for interactions and contraindications, including anticoagulant use, across your whole picture when you use the platform.
Guideline positions
The NIH Office of Dietary Supplements sets adequate intakes at 120mcg for men and 90mcg for women, records that no upper intake level was established because no adverse effects have been reported, and states that people on warfarin need consistent vitamin K intake. Schurgers and colleagues (Blood, 2007) showed MK-7 is well absorbed with a much longer half-life than K1. Knapen and colleagues (Osteoporosis International, 2013) found 180mcg MK-7 daily for three years reduced bone loss measures in postmenopausal women.
Practical framework
Choose MK-7 when you supplement vitamin D3 or calcium and want the vitamin K side of calcium handling covered, or where bone density is the concern and diet is light on greens and fermented foods. Vitamin K2 provides 150mcg of MK-7 per capsule at £31.68 for the bottle, in stock and UK-made, at nutritailor.co.uk/products/vitamin-k2. Take with a meal containing fat. If you take warfarin or any anticoagulant, speak to your anticoagulant clinic or prescriber before starting, and do not change an existing K2 habit abruptly.
Common misconceptions
The claim that K2 removes existing arterial calcium overstates the evidence; the observational data link higher menaquinone intake with less calcification and lower coronary risk, but intervention trials are few and the honest position is promising rather than proven. Another misconception is that people on warfarin should avoid all vitamin K, when their clinics actually aim for consistent intake rather than zero. Finally, K1 from greens does not convert freely into MK-7; MK-4 is the form the body makes from K1, and MK-7 comes from fermented foods or supplements.
Sources
- NIH Office of Dietary Supplements 2021. Vitamin K Fact Sheet for Health Professionals. NIH ODS.
- Schurgers LJ et al 2007. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood 109:3279-83.
- Knapen MH et al 2013. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int 24:2499-507.