VitaminsThin

Vitamin K2

Also called: menaquinone, MK-7, MK-4, menatetrenone.

A form of vitamin K sold for bones and arteries, where the real issue lies with vitamin K antagonist anticoagulants.

What it is

Vitamin K activates vitamin K-dependent proteins, including clotting factors and bone and vascular proteins. K1 (phylloquinone) comes from green vegetables, K2 (menaquinones, including MK-4 and MK-7) from fermented foods and animal foods. It is sold mostly paired with vitamin D.

What the label does not say

The Linus Pauling Institute writes that up to 100 mcg per day of phylloquinone is considered safe in someone on warfarin, but that the stability of anticoagulation can be compromised by MK-7 doses as low as 10 to 20 mcg per day. That is well below the doses used in trials, including one cited trial at 375 mcg per day.
MK-4 and MK-7 do not behave the same way in the blood. Two products labelled vitamin K2 are therefore not interchangeable, and the label does not say so.
The NIH concludes that the role of the different forms of vitamin K in arterial calcification and coronary risk remains uncertain. A 3-year trial with phylloquinone showed no difference in coronary calcification.
No upper limit has been set, the panel having judged the potential for toxicity low. The absence of a limit says nothing about effectiveness, only about toxicity.

The forms on the shelf

MK-4: found in animal foods and made by the body from phylloquinone. In a study of healthy women, a single 420 mcg dose of MK-4 did not make MK-4 detectable in the serum of any participant, and 60 mcg per day for 7 days did not raise serum MK-4.
MK-7: from fermented foods such as natto. In the same study, MK-7 reached its serum peak at 6 hours and remained detectable for 48 hours. The NIH indicates that it is well absorbed and has a longer half-life than phylloquinone.
Pharmacological doses of MK-4 (45 mg per day) used in Japan for osteoporosis: nothing like the micrograms in everyday supplements.

Published reference values

Adequate intake (there is no recommended intake, for lack of data): 120 mcg per day for adult men, 90 mcg for women.
Upper limit: none has been set.
These values cover vitamin K as a whole; the NIH sets no separate benchmark for K2.

When

Fat-soluble, so with a meal containing fat. For someone on a vitamin K antagonist, consistency of intake matters more than the time you take it.

Keep apart from

Warfarin and other vitamin K antagonists: the NIH indicates that a consistent vitamin K intake is necessary, because a sudden change can increase or decrease the anticoagulant effect. This is not a matter of spacing doses by the hour, but a medical decision.

To mention to a professional

Use of a vitamin K antagonist anticoagulant, clotting disorder, pregnancy and breastfeeding: check with a health care professional before any K2 supplement.

What it is sold for, and what the data show

K2 is sold to steer calcium toward bone rather than arteries. Observational data do associate a high menaquinone intake with less severe aortic calcification, but several small trials in at-risk populations reported no benefit on the progression of vascular calcification. On the bone side, a 2019 meta-analysis reports a reduction in clinical fractures, with no effect on vertebral fractures or bone density. The promise outruns what the trials show for now.

From the plate first

Natto is by far the most concentrated source of MK-7: about 850 mcg per 3 ounces according to the NIH. Cheeses and other fermented foods, chicken, eggs and dairy products provide modest amounts. Green vegetables mostly provide K1.

Sources

Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.