Vitamin K2 Foods: Best Sources, Benefits and Safety

01K1 vs K2

Vitamin K1 versus K2

Vitamin K1 (phylloquinone) is the main dietary form and is found in green leafy vegetables such as kale, spinach and broccoli, and in vegetable oils. Vitamin K2 (menaquinones) is found in fermented foods and animal products and is also produced in small amounts by gut bacteria. Different menaquinones are named by the length of their side chain, from MK-4 to MK-13. Longer-chain forms such as MK-7 stay in the blood longer than K1, and a study comparing them found MK-7 had a longer half-life and more potent effect on blood clotting factors when taken as a supplement.

02Foods

Best vitamin K2 foods

• Natto: fermented soybeans with by far the highest MK-7 content, often several hundred micrograms or more per 100 g.
• Hard cheeses: such as Gouda, Edam and Emmental, with tens of micrograms per 100 g.
• Soft cheeses: such as brie and camembert.
• Curd cheese and some fermented dairy.
• Egg yolks: contain MK-4, depending on the hen’s diet.
• Chicken, especially dark meat.
• Butter and full-fat dairy, in small amounts.
• Liver and liver pâté: contain K2 but are high in vitamin A, so not suitable in pregnancy.
• Values vary widely depending on production methods and bacteria used.

03Fermented

Fermented foods and K2

Fermentation with certain bacteria produces menaquinones. Natto, made with Bacillus subtilis, is the standout source. Sauerkraut and other fermented vegetables contain much smaller amounts, and yoghurt and kefir vary. Fermented foods have other potential gut benefits; see our guide to fermented foods for gut health.

04Role

What vitamin K does in the body

• Activates clotting factors made in the liver, essential for normal blood clotting.
• Activates osteocalcin, a protein involved in bone mineralisation.
• Activates matrix Gla protein, which helps prevent calcium deposits in blood vessel walls.
• Newborns receive a vitamin K injection at birth to prevent bleeding, because they have low levels.

05Heart

Vitamin K2 and heart health

In the Rotterdam Study, a large Dutch population study, people with the highest intake of menaquinones had a lower risk of coronary heart disease and less severe aortic calcification than those with the lowest intake, while K1 intake showed no such association. Another study in postmenopausal women found that higher menaquinone intake was associated with less coronary artery calcification. These are observational findings and cannot prove cause and effect, as K2-rich diets may differ in other ways. Trials of K2 supplements on heart outcomes are ongoing.

06Bones

Vitamin K2 and bone health

A three-year randomised trial in healthy postmenopausal women found that 180 micrograms of MK-7 a day reduced age-related decline in bone mineral density at the lumbar spine and femoral neck and helped maintain bone strength compared with placebo. In Japan, high-dose MK-4 is used as a treatment for osteoporosis. Overall, research is promising but mixed, and vitamin K2 is not a replacement for established osteoporosis treatments, calcium, vitamin D and exercise.

07How much

How much vitamin K do you need?

There is no separate recommendation for vitamin K2. The NHS states that adults need approximately 1 microgram of vitamin K a day for each kilogram of body weight, and that most people get enough from a varied diet. In the US, adequate intakes for total vitamin K are 120 micrograms a day for men and 90 micrograms for women. Vitamin K is fat-soluble, so it is absorbed better when eaten with some fat.

08Supplements

Should you take a K2 supplement?

• Most people do not need one if they eat a varied diet.
• K2 supplements, often as MK-7, are sometimes combined with vitamin D.
• The NHS says taking 1 mg or less of vitamin K supplements a day is unlikely to cause harm.
• Do not take vitamin K supplements if you are on warfarin unless your doctor advises.
• Talk to a doctor or dietitian before taking supplements, especially if you have a medical condition.

09Warfarin

Vitamin K2 and warfarin

Warfarin works by blocking the recycling of vitamin K. Sudden increases in vitamin K intake can make it less effective, increasing the risk of clots, while sudden decreases can increase bleeding risk. Long-chain K2 such as MK-7 can affect clotting at relatively low supplement doses. People on warfarin do not need to avoid vitamin K foods but should keep intake steady. Newer anticoagulants, such as apixaban and rivaroxaban, are not affected by vitamin K in the same way.

10Day

Easy ways to include K2

• Try natto with rice and spring onions, if you enjoy its strong flavour.
• Add a little hard cheese to salads, omelettes or vegetables.
• Include eggs in breakfast or lunch.
• Choose chicken thighs or drumsticks occasionally.
• Pair with leafy greens for vitamin K1.

11Deficiency

Who might be low in vitamin K?

• Newborn babies, which is why a vitamin K injection is offered at birth.
• People with conditions that reduce fat absorption, such as coeliac disease, Crohn’s disease, cystic fibrosis or after bariatric surgery.
• People taking long courses of some antibiotics, which can affect gut bacteria.
• People with very restricted diets.
• Signs of deficiency include easy bruising and bleeding; a doctor can check clotting with a blood test.
• For general bone-healthy eating, our guide to foods for menopause covers calcium and vitamin D.

12Summary

Key points to remember

• Vitamin K2 is found in fermented foods and some animal products.
• Natto is the richest source; cheese and eggs provide smaller amounts.
• Research on bones and heart is promising but not conclusive.
• People on warfarin should keep vitamin K intake consistent.