Vitamin K comes in two main forms: K1 and K2.¹

K1 is the one in green vegetables, and it's where most people get their vitamin K.¹ K2 is the one in fermented foods, like natto and some cheeses. You also get small amounts from meat, eggs, and dairy.¹ Vitamin K is a fat-soluble vitamin. That means your body stores it in fat, rather than flushing out what it doesn't use straight away.¹

What does vitamin K2 do in the body?

Vitamin K contributes to normal blood clotting.^2,3

Vitamin K contributes to the maintenance of normal bones.^2,3

Here's what sits behind both.

Your body makes certain proteins that only switch on when vitamin K is there.¹ Two of them matter here. One is called prothrombin. It helps your blood clot when you cut yourself.¹

The other is called osteocalcin. It's found in your bones, and it may play a part in how bone is built and renewed.¹ That's how the vitamin works inside you. It isn't a description of what happens if you take a supplement.

Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle.

Vitamin K2 and your heart

There's another vitamin K protein called matrix Gla protein. It sits in the walls of your blood vessels. Researchers think it might affect how calcium builds up there.¹

A large study in the Netherlands, called the Rotterdam Study, looked at what people ate, and it found that people who ate more K2 were less likely to die of heart disease than people who ate the least.⁶ Eating more K1 made no difference to any of the results.⁶

But that study only shows a link. It doesn't show that taking K2 stops heart disease. People who eat more K2 might differ in other ways too. Trials that tested this properly haven't settled it either. The National Institutes of Health says the results have been mixed, and that we still don't know what role vitamin K plays here.¹ In one trial of 388 adults aged 60 to 80, taking vitamin K made no significant difference to calcium build-up in their arteries.¹

Which foods contain vitamin K2?

Mostly fermented foods, plus smaller amounts in meat, dairy, and eggs.¹

One thing to know first. Scientists have measured K1 in foods far more than K2, so there's less data on K2 than you'd expect.¹ The amounts below are the ones measured as K2.

Look at the top of that list. Natto has more than sixty times as much as anything else. That's why it comes up in nearly every article about K2.

If you're vegetarian, your K2 comes from cheese, eggs, and dairy.¹

If you're vegan, natto is the only plant food with much in it.¹ It's sticky, it smells strong, and it's fair to say it's an acquired taste. One more thing about fermented foods - the amount of K2 depends on which bacteria were used and how long it fermented.¹ So two cheeses won't have the same amount, and neither will two batches of sauerkraut.

MK-4 and MK-7: what's the difference?

These are the two types of K2 you'll see on labels.

Most UK supplements use MK-7. That includes Numan's Vitamin D3 with K2.

How much vitamin K2 do you need?

There's no separate figure just for K2. UK advice gives one amount for vitamin K as a whole.

Adults need about 1 microgram a day for every kilo they weigh.⁴

So if you weigh 65kg, that's about 65 micrograms a day. If you weigh 75kg, it's about 75.⁴

You should get all you need from eating a varied, balanced diet.⁴ You don't need it every single day either. Your liver stores what you don't use right away.⁴

On a label, vitamin K is shown as a percentage. That percentage is based on a set amount.

Is 200µg of vitamin K2 too much?

No. Taking 1mg a day or less is unlikely to do any harm.⁴ 1mg is 1,000µg, so 200µg is a fifth of that. That said, if you take vitamin K supplements, don't take too much. It might be harmful.⁴

Can you be low in vitamin K?

It's rare, if you're otherwise well. Being properly low in vitamin K hardly ever happens in healthy adults.¹ When it does, it's usually in people whose bodies struggle to absorb food, or people on medicines that block vitamin K.¹

In fact, if you eat a varied diet, it's almost impossible to get low enough for it to show up on a blood clotting test.¹ When someone is very low, the main signs are bleeding and bruising more easily than normal. These only show up in severe cases.¹Some people are more likely to be low. That includes newborn babies, people who've had weight loss surgery, and people with conditions that affect how they absorb food, like coeliac disease, cystic fibrosis, ulcerative colitis, or short bowel syndrome.¹ If you're bruising or bleeding more easily than usual, see a GP. That's a symptom worth getting checked, not a reason to start a supplement.

Side effects and who shouldn't take it

If you take warfarin

Do not take the herbal remedy St John's wort or vitamin K supplements while you're taking warfarin.⁵

Warfarin is a blood thinner. It works by blocking vitamin K.¹ So if you change how much vitamin K you take in, you change how well your warfarin works.¹ That works both ways. Taking more vitamin K can weaken it. Suddenly taking less can make it too strong.¹ Either is a problem.

Food matters too, though less dramatically. Green veg like broccoli and spinach can affect how warfarin works. You can still eat them. Just talk to your warfarin clinic.⁵ Don't start or stop a vitamin K supplement without speaking to your doctor or warfarin clinic first.

If you take orlistat

Orlistat is a weight loss medicine. It stops your body absorbing some of the fat you eat.¹

Vitamin K is a fat-soluble vitamin, so it travels with fat. That means orlistat can reduce how much vitamin K you absorb too.¹ If you take orlistat and warfarin together, that combination can affect your blood clotting more than either alone.¹ 

A pharmacist can answer most interaction questions for free, and they’re usually the fastest route. If you’d rather talk it through properly with a doctor, you can book a private consultation with Numan.

Other medicines

Antibiotics kill off some of the gut bacteria that make vitamin K.¹ Some cholesterol medicines, called bile acid sequestrants, can stop you absorbing it properly.¹

If you take either regularly, mention vitamin K to your doctor or pharmacist.¹

Everyone else

If you're pregnant, breastfeeding, taking any medicine, or have a health condition, speak to a healthcare professional before starting a supplement. For details about the product itself, see the Vitamin D3 with K2 safety information.

The numan take

You should get all the vitamin K you need from a varied, balanced diet,⁴ and being low is rare in healthy adults.¹ Vitamin D is the one worth thinking about. From October to early March, you can’t make it from sunlight in the UK.⁷That’s why the two are often sold together, and why our Vitamin D3 with K2 puts both in one tablet. There’s more on why vitamin D3 and K2 are often taken together. Not sure what you need? Have a look at the Numan supplement range and see what fits. Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle.

References

1. ^{National Institutes of Health, Office of Dietary Supplements. Vitamin K: fact sheet for health professionals [Internet]. Bethesda (MD): NIH ODS [cited 2026 Oct 23]. Available from: https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/}

2. ^{Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register [Internet]. London: DHSC [cited 2026 Oct 23]. Available from: https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register}

3. ^{Nutraceuticals Group. Full list of EFSA health claims [Internet]. Nutraceuticals Group [cited 2026 Oct 23]. Available from: https://nutraceuticalsgroup.com/uk/full-list-of-efsa-health-claims}

4. ^{National Health Service. Vitamins and minerals: vitamin K [Internet]. London: NHS; 2020 [page last reviewed 2020 Aug 3; cited 2026 Oct 23]. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-k/}

5. ^{National Health Service. Warfarin [Internet]. London: NHS; 2026 [page last reviewed 2026 Feb 24; cited 2026 Oct 23]. Available from: https://www.nhs.uk/medicines/warfarin/}

6. ^{Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100-5. doi:10.1093/jn/134.11.3100}

7. ^{National Health Service. Vitamins and minerals: vitamin D [Internet]. London: NHS; 2020 [page last reviewed 2020 Aug 3; cited 2026 Oct 23]. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/}