Vitamin K2 and Bone Health: What the Evidence Actually Shows

Vitamin K2 is a form of vitamin K, found in fermented foods like natto and in cheese, that helps activate proteins involved in building bone, but the evidence that K2 supplements protect bones or prevent fractures is mixed. Some trials, mostly Japanese ones using very high doses, look encouraging. European trials of the K2 sold in UK supplements have given mixed results, and none has shown fewer fractures. The UK has no K2 recommendation, and vitamin K supplements are unsafe for anyone taking warfarin without specialist advice.

What is vitamin K2 and how is it different from K1?

Vitamin K is a family of compounds. Vitamin K1 (phylloquinone) comes mainly from plants, and vitamin K2 is a group of related compounds called menaquinones, labelled "MK" plus a number that reflects the length of the molecule. The two you will see on supplement labels are MK-4 and MK-7.

The NHS describes vitamin K as "a group of vitamins that the body needs for blood clotting, helping wounds to heal," and adds that "there's also some evidence vitamin K may help keep bones healthy" NHS. Its role in bone is to help activate osteocalcin, a protein made by bone-building cells that helps bind calcium into bone. When vitamin K is low, more osteocalcin circulates in an inactive ("undercarboxylated") form. That is the biological reason researchers became interested in K2.

The NHS does not set separate targets for K1 and K2. It says adults need about 1 microgram of vitamin K per kilogram of body weight a day, so about 65 micrograms for someone weighing 65kg, and that most people can get this from their diet NHS.

Which foods contain vitamin K2?

Natto, a Japanese dish of fermented soybeans, is by far the richest food source of vitamin K2 (MK-7). Cheese, chicken, beef and sauerkraut contain moderate amounts. A 2022 review in Frontiers in Pharmacology reports that MK-7 levels are "highest in natto; moderate in chicken, sauerkraut, beef and a variety of cheeses", and that shorter menaquinones like MK-4 "are found majorly in animal-based food products" Frontiers in Pharmacology, 2022. Bacteria in the gut also make some menaquinones.

In practice, most people in the UK eat very little natto, so the K2 in a typical British diet comes mainly from cheese and other animal foods. Amounts vary between products, and UK food labels don't usually list K2, so there is no reliable "K2 per portion" chart to follow.

Vitamin K1 is easier to get: the NHS lists green leafy vegetables such as broccoli and spinach, vegetable oils and cereal grains as good sources NHS. If you want to eat for your bones, a diet with plenty of greens, enough calcium-rich foods and some dairy or fermented foods covers vitamin K without special effort.

Does vitamin K2 actually help your bones?

Possibly a little, but the evidence is inconsistent, and the strongest positive results come from trials that may not apply to people in the UK. Here is what the main studies found, in plain terms.

Japanese trials of high-dose MK-4. A 2006 meta-analysis in Archives of Internal Medicine found that all seven trials reporting fractures were Japanese and used menaquinone. Pooled together, they showed large reductions in vertebral, hip and non-vertebral fractures Arch Intern Med, 2006. But those results later came under serious doubt. In 2018 the authors updated their analysis, and a letter in JAMA Internal Medicine from independent researchers noted that "3 of 7 contributing trials are problematic", arguing that the updated conclusions no longer matched the updated analysis JAMA Intern Med, 2018. The doses in this research are also very high. Several trials used 45mg (45,000 micrograms) of menatetrenone a day Front Public Health, 2022, roughly 700 times the NHS daily vitamin K requirement for a 65kg adult.

A 2022 meta-analysis. Pooling 16 randomised trials in postmenopausal women (6,425 participants), researchers found an improvement in lumbar spine bone density, but no significant difference at the hip or femoral neck. The spine benefit was significant only when K2 was combined with other treatment, not with K2 alone. For fractures, the overall result was not statistically significant (risk ratio 0.56, 95% CI 0.28–1.11). It became significant only after the authors left out one large trial, a step they said might introduce bias and that needs confirming in bigger studies. The authors still concluded K2 was effective, but nine of the 16 trials were Japanese, and the authors questioned whether the benefits apply elsewhere Front Public Health, 2022.

European trials of MK-7 (the type in most UK supplements). The results disagree:

• In the Netherlands, 244 healthy postmenopausal women took 180 micrograms of MK-7 a day for three years. The supplement slowed age-related loss of bone density at the lumbar spine and femoral neck, but not at the total hip Osteoporos Int, 2013.
• In Norway, 334 women in early menopause took 360 micrograms of MK-7 a day for a year. It changed a blood marker (less inactive osteocalcin) but "did not influence bone loss rates" Osteoporos Int, 2010.

Neither European trial was designed to show whether K2 prevents fractures, which is what really matters.

Is vitamin K2 recommended for bone health in the UK?

No. There is no UK recommendation to take vitamin K2 for bone health, and UK osteoporosis guidance does not include it. The NHS gives a single vitamin K requirement, does not separate K1 from K2, and says "there's not enough evidence" to know the effects of taking high-dose vitamin K supplements every day. It adds that taking 1mg or less a day is unlikely to cause harm NHS.

The UK's national osteoporosis guideline (NOGG) sets out non-drug advice on calcium, vitamin D, protein, exercise, alcohol and smoking, and does not include a vitamin K recommendation NOGG, 2024. The nutrients with the clearest UK guidance are calcium and vitamin D, alongside protein and regular weight-bearing exercise.

Is vitamin K2 safe with warfarin and other medicines?

If you take warfarin, don't take vitamin K2 or any other vitamin K supplement unless your anticoagulant clinic or doctor has said it's safe. Warfarin works by blocking vitamin K, so extra vitamin K can make it less effective and increase the risk of a clot.

People on newer anticoagulants (such as apixaban or rivaroxaban), or on any regular medicine, should also check with a pharmacist before starting a supplement, because combination products can contain several active ingredients.

Should you take a vitamin K2 supplement for your bones?

For most people, there is no strong reason to take one. A varied diet supplies the vitamin K you need, and the evidence does not show K2 supplements prevent fractures. If you are healthy and not on warfarin, a modest-dose K2 supplement is unlikely to harm you, but it shouldn't take the place of the measures with clearer evidence:

1. Get enough calcium from food (700mg a day for most adults). See our calcium-rich foods chart.
2. Take vitamin D in autumn and winter, as the NHS advises. See vitamin D for bone health.
3. Do regular weight-bearing and resistance exercise, eat enough protein, don't smoke and keep alcohol low.
4. If you have osteoporosis, take your prescribed treatment as directed. K2 is not a substitute, and you should never stop or change osteoporosis medicine without talking to your doctor.

Other nutrients get similar attention, such as magnesium. The pattern is the same: food first, and supplements only for a clear reason. Our osteoporosis diet guide shows how it fits together.

How can you tell whether your bones are actually changing?

Supplements don't come with feedback. The only way to know how your bones are doing is to measure them over time. If you have risk factors for osteoporosis, ask your GP about a fracture risk assessment and, where appropriate, a DEXA scan, which is the UK standard for diagnosis.

If you want a baseline before any of that, or a way to monitor change without repeated X-rays, Screen My Bones offers a radiation-free REMS bone health assessment of the spine and hip. It is a screening and monitoring option, not a replacement for a DEXA scan when a formal diagnosis is needed.

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This article is part of our nutrition and supplements series.