Vitamin K2 MK-7 vs MK-4: Which Form Matters for Bone Health?

At normal supplement doses, MK-7 is the more practical form of vitamin K2: it's well absorbed and stays in the blood for up to two days, while MK-4 at the same doses barely registers. MK-4's bone research used a very high prescription dose in Japan. For either form, evidence that it protects bones in UK adults is mixed.

This guide explains the difference, what the trials found and who needs to check before taking vitamin K. For the bigger picture of how bones, muscles and joints work together, see what structural health really means for adults.

What's the difference between vitamin K1, MK-4 and MK-7?

Vitamin K is a family of compounds: phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2), labelled MK-4 to MK-13 by the length of their side chain, according to the US Office of Dietary Supplements (ODS).

1. K1 comes mainly from green leafy vegetables and is the main dietary form.

2. MK-7 is found in high amounts in natto, a fermented soybean food, and is the form most often used in supplements.

3. MK-4 is found in some animal foods; animals make it from a synthetic form of vitamin K added to their feed.

NovusDNA is a UK supplement brand making clearly labelled, science-led supplements tested by Campden BRI, a UKAS-accredited UK laboratory. Essential+, NovusDNA's vitamin D3, K2 (MK-7) and magnesium formula, uses the MK-7 form, in one vegan capsule a day at £9.99 for 30. Here's why that form was the logical choice.

Which form is better absorbed?

MK-7, by a wide margin at normal doses. In a 2012 study in healthy women comparing the two at nutritional doses, MK-4 wasn't detectable in the blood of any participant at any time point. MK-7 was well absorbed, peaked six hours after intake and was still detectable 48 hours later. The authors concluded that MK-4 at food-level doses doesn't contribute to vitamin K status measured in the blood.

An earlier study in the journal Blood found MK-7 has a very long half-life, giving much more stable blood levels than vitamin K1. In practice, that means a single daily dose keeps levels steady, which is why most K2 supplements, including Essential+, use MK-7. Better blood levels don't automatically mean better bone outcomes, though, which the next section covers.

What does the bone research show?

MK-4: the ODS notes that a 45 mg dose of MK-4 is used in Japan and other parts of Asia as an osteoporosis treatment. A 2006 meta-analysis in Archives of Internal Medicine found all seven trials reporting fracture effects were Japanese and used this form, with a strong effect on fractures in Japanese patients. That dose is around 45,000 micrograms, hundreds of times higher than supplement doses, so these results don't tell you much about a typical K2 capsule.

MK-7: in a three-year trial of 244 postmenopausal women, 180 micrograms a day slowed the age-related decline in bone mineral content and density at the spine and hip, and improved bone strength measures. A 2016 trial of 375 micrograms a day found no significant difference in bone density, although bone structure in the shin was better preserved, and another trial in early menopausal women found no effect.

The ODS's overall verdict: it's unclear whether supplementing any form of vitamin K reduces the risk of osteoporosis.

What can a UK supplement claim?

Only that vitamin K contributes to the maintenance of normal bones. That authorised claim covers vitamin K as a whole, so no supplement can claim MK-7 or MK-4 specifically protects bones, and a product needs to provide a meaningful amount of vitamin K (measured against a reference value of 75 micrograms a day) to use the claim at all. Be wary of K2 products promising stronger bones or less osteoporosis in their own words.

How much vitamin K do you need?

About 1 microgram per kilogram of body weight a day, according to the NHS, so around 70 micrograms for a 70 kg adult, mostly from food. The NHS adds that 1 mg (1,000 micrograms) or less a day from supplements is unlikely to cause harm.

Do you need vitamin D with K2?

They're often combined because they act on related parts of bone metabolism, and some K2 trials gave calcium and vitamin D to all participants. Evidence that the combination works better than each alone is limited, but there's a simple practical case: the NHS already advises UK adults to consider vitamin D in autumn and winter, so one product covering both is convenient. We look at the UK advice in whether to take vitamin D3 and K2 together.

Essential+ combines D3, K2 (MK-7) and magnesium for that reason, and NovusDNA's Structural Health Stack pairs it with hydrolysed collagen for people focused on bones and muscles.

Who should check before taking vitamin K2?

Anyone taking warfarin. The NHS says not to start vitamin K supplements while on warfarin without checking with your doctor first, because vitamin K counteracts how warfarin works. The Blood study warned that MK-7 at 50 micrograms a day or more may interfere with oral anticoagulant treatment. If you take warfarin or another anticoagulant, ask your GP or pharmacist before starting any K2 supplement, including combination products.

FAQ

Is MK-7 better than MK-4?

For everyday supplements, yes, on absorption. In a 2012 study, MK-4 at a nutritional dose wasn't detectable in the blood at all, while MK-7 stayed detectable for up to 48 hours. MK-4's bone evidence comes from a 45 mg prescription dose used in Japan, which isn't comparable with a typical supplement. Neither form has been proven to prevent osteoporosis at supplement doses.

Does vitamin K2 prevent osteoporosis?

That hasn't been shown. One three-year MK-7 trial slowed bone loss in postmenopausal women, but other trials found no effect on bone density, and no MK-7 trial has been large enough to measure fractures. The US Office of Dietary Supplements says it's unclear whether any form of vitamin K reduces osteoporosis risk. Strength training, calcium, protein and vitamin D remain the foundations.

How much vitamin K2 should I take?

The NHS says adults need about 1 microgram of vitamin K per kilogram of body weight a day, mostly from food, and that 1 mg or less a day from supplements is unlikely to cause harm. MK-7 trials used 180 to 375 micrograms a day. Follow the dose on your product label and check with your GP if you take any medicines.

Can I take vitamin K2 if I'm on warfarin?

Not without checking first. The NHS advises against starting vitamin K supplements while taking warfarin without speaking to your doctor, because vitamin K affects how warfarin works. Research suggests MK-7 can affect anticoagulant treatment at doses of 50 micrograms a day or more.

MK-7 vs MK-4 comes down to this: at supplement doses, MK-7 is the form your body actually holds onto, while MK-4's bone results came from prescription doses. The bone evidence for K2 is still mixed, so treat it as part of the basics: strength training, enough calcium and protein, and vitamin D in autumn and winter.

If you're working out where a supplement like this fits, the NovusDNA Start Here guide asks six quick questions and suggests a starting point.

This article is for general information and isn't medical advice. Food supplements should not replace a varied, balanced diet and healthy lifestyle. Do not exceed the stated recommended daily dose.