Vitamin K2: Uses, Benefits, Dosage & Safety

Last updated: June 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy

What is Vitamin K2?

Vitamin K2 (menaquinone) is one of the two main forms of vitamin K, alongside vitamin K1 (phylloquinone) from leafy greens. K2 is most concentrated in fermented foods — natto, a fermented soybean dish, is by far the richest source — with smaller amounts in some cheeses, egg yolk and organ meats. Supplements usually supply either the MK-4 or the MK-7 sub-type; MK-7 is the more popular because it stays active in the bloodstream far longer, so a small daily dose is enough. K2 is not a quick-acting supplement: it works in the background as a helper for proteins that decide where calcium ends up in the body.

What Vitamin K2 is commonly used for

In the supplement world, Vitamin K2 is taken mainly for bone support and for arterial or 'heart and calcium' health, and it is often paired with vitamin D and calcium. It is also marketed within skin & anti-aging and longevity formulas. These are areas of nutritional support and active research, not proof that a supplement prevents fractures or heart disease — the marketing usually runs ahead of the hard outcome data.

How Vitamin K2 works

Vitamin K2 acts as a cofactor for an enzyme that 'activates' certain proteins through a process called carboxylation. Two of these proteins matter most. Osteocalcin, made by bone-building cells, helps bind calcium into the bone matrix once it is carboxylated. Matrix Gla protein (MGP) helps keep calcium from depositing in artery walls. When vitamin K is in short supply, more of these proteins stay in their inactive, 'undercarboxylated' form — which is the marker most K2 trials are able to move. The idea that K2 helps put calcium where it belongs follows from this biology, though proving it changes fractures or heart events needs much larger and longer trials.

What the evidence says

Here's an honest snapshot of what published research suggests about Vitamin K2 — including where the evidence is limited.

• A 3-year randomised, placebo-controlled trial in 142 postmenopausal women with osteopenia found MK-7 (375 µg/day) sharply reduced undercarboxylated osteocalcin — a marker of vitamin K status — versus placebo, though effects on bone density were modest. (PubMed)
• A scientific review summarises how vitamin K2 supports both bone and cardiovascular health by improving how the body distributes calcium, while noting the limits of current outcome data. (PubMed)
• General background on vitamin K forms, food sources, dosing and safety is summarised by reputable health references. (MedlinePlus)

Typical dosage used in studies

Trials of MK-7 most commonly use about 90–360 µg per day, taken with a meal containing some fat for absorption. Some Japanese bone studies use a much higher 45 mg/day of the MK-4 form, which is a pharmaceutical-level dose rather than a typical supplement amount. Changes in vitamin K status markers appear within weeks, but any effect on bone builds over months. This is general information from research, not a dosing instruction.

Side effects and safety

Vitamin K2 is generally well tolerated in studies, with few side effects reported even over years of use. It is fat-soluble, but unlike vitamins A and D it has not shown meaningful toxicity at supplement doses. The main safety issue is not the vitamin itself but its interaction with one specific class of medication (below).

Medication interactions and who should avoid Vitamin K2

Sources & further reading

The evidence summary above is drawn from these sources. For general, authoritative background you can also consult:

• PubMed-indexed study (PMID 33030563)
• PubMed-indexed study (PMID 26770129)
• MedlinePlus
• NIH Office of Dietary Supplements
• NIH National Center for Complementary and Integrative Health

Frequently asked questions

Is vitamin K2 the same as vitamin K1?

No. Vitamin K1 (phylloquinone) comes mainly from leafy greens and is used mostly for blood clotting. Vitamin K2 (menaquinone) comes from fermented foods and animal products, stays active longer, and is the form studied most for bone and arterial health.

What is the difference between MK-4 and MK-7?

Both are forms of K2. MK-7 has a much longer half-life in the blood, so a small once-daily dose works; MK-4 is cleared quickly and is used at far higher, more frequent doses in research. Most modern supplements use MK-7.

Does vitamin K2 strengthen bones?

K2 reliably improves vitamin K status markers like undercarboxylated osteocalcin, and some trials show small benefits to bone density. Large trials proving it prevents fractures are still lacking, so it is best seen as supportive, not a treatment for osteoporosis.

Can I take vitamin K2 with vitamin D?

They are commonly combined, and the rationale is reasonable: vitamin D increases calcium absorption while K2 is thought to help direct that calcium. The combination is generally considered safe, but strong proof that it changes hard outcomes like fractures or heart events is still limited.

Is vitamin K2 safe with blood thinners?

Not without medical advice. K2 interacts with warfarin and similar vitamin-K-antagonist drugs and can throw off clotting control. Talk to your doctor or anticoagulation clinic before using it.