Vitamin K2 is a fat-soluble vitamin form within the K family. It includes menaquinones such as MK-4 and MK-7. Vitamin K1, or phylloquinone, is the main dietary form and occurs mostly in green vegetables. Both help activate proteins involved in normal blood clotting.
Claims for K2 often suggest it “directs” calcium into bone and away from arteries. That oversimplifies the role of vitamin K. Research suggests that vitamin K2 may activate a carboxylation system involving osteocalcin and matrix Gla protein (MGP), but changing a vitamin K-dependent protein biomarker does not prove fewer fractures or cardiovascular events.
Written by: Charles Gumbley, BHSc Clinical Nutrition, DipHSc Western Herbal Medicine. Evidence checked: 20 July 2026.
Vitamin K1 and K2: Dietary Sources of Vitamin K
The differences between vitamin K1 and vitamin K2 include their structures and food sources. Vitamin K1 is found mainly in leafy greens and plant oils. Vitamin K2 is found in animal and fermented food products; natto is especially rich in vitamin K2 as MK-7, while cheese and other foods contain smaller, variable amounts. Sauerkraut is not a reliable source because its K2 content depends on the culture and production method.
Australian reference intakes for vitamin K cover the total nutrient, not vitamin K2 specifically. The adequate dietary intake of vitamin K is 70 micrograms a day for adult men and 60 for adult women, including during pregnancy and breastfeeding. There is no separate K2 intake target or established upper level. “No upper level” does not establish unlimited supplemental safety.
Vitamin K deficiency is uncommon from diet alone in healthy adults. Malabsorption, some medicines and prolonged low intake can affect vitamin K status. Measuring circulating vitamin K or undercarboxylated protein is not a routine wellness test; interpretation belongs with a clinician.
Benefits of Vitamin K2 for Bone Health: What Trials Show
The functions of vitamin K make bone health a reasonable research question. Osteocalcin carboxylation changes with supplementation. However, an updated systematic review found no reliable improvement in bone mineral density or vertebral fractures after excluding trials at high risk of bias. Evidence for clinical fractures remained insufficient.
Some trials in postmenopausal women used pharmacological MK-4 doses unlike everyday K2 supplements. Adding vitamin K2 to your diet should not replace osteoporosis assessment or prescribed treatment. Adequate calcium, vitamin D, resistance exercise and individual risk management remain separate considerations.
Vitamin K2 and Cardiovascular Health: Vitamin K-Dependent Proteins
MGP is studied because its active form could inhibit abnormal calcification. Supplementation reliably lowers inactive dp-ucMGP, yet the cardiovascular evidence is inconsistent. A 2020 systematic review found too few well-conducted, adequately powered trials to show that K2 helps reduce the risk of heart disease.
A later trial gave 365 men MK-7 plus vitamin D3 for 24 months. Biomarkers changed, but aortic-valve and coronary calcium progression did not; nor did surgery, death or cardiovascular events. A small pooled effect in a 2023 meta-analysis needs rigorous confirmation. Vitamin K2 is not a treatment for arterial calcification or heart disease.
Vitamin K2 Supplements: K2 Intake, Vitamin D3 and Warfarin Safety
Vitamin D supports calcium absorption, but that does not mean every user needs K2. Trials do not establish a universal D3-and-K2 ratio. A clinician can assess diet, bone risk, medicines and the reason for supplementation.
Vitamin K can seriously affect warfarin and similar antagonists used to prevent blood clots. Do not start, stop or change a K2 product without the prescriber or anticoagulation service. Keep food and supplement intake consistent. Other anticoagulants work differently, but medicine-specific advice is still necessary.
Vitamin K supplements vary by form, dose and other ingredients. Possible health effects include digestive upset or allergy, while long-term high-dose safety is uncertain. Check first if you are pregnant, breastfeeding, preparing for surgery, have liver or malabsorption disease, or use anticoagulants, bile-acid sequestrants, orlistat or prolonged antibiotics.
Nutrition Market sells vitamin products, which creates a commercial conflict. No K2 product is ranked or linked here until its form, dose, ARTG status, approved indications, warning statements, stock, cost and margin pass the governed feed checks.
Vitamin K2 Questions
What happens if you take vitamin K2 every day?
Daily K2 may change vitamin K-dependent biomarkers, but proven long-term benefits and the ideal dose are uncertain. It may be unsafe with warfarin or another vitamin K antagonist. Do not assume that a lack of an upper level makes high doses risk-free.
Should you take D3 and K2 together?
Not automatically. Vitamin D3 and K2 have related roles in calcium and bone biology, but clinical trials have not established that every vitamin D user benefits from adding K2. Seek individual advice when treating a deficiency or bone condition.
How to get K2 naturally?
Natto is among the most concentrated vitamin K2-rich foods. Some cheeses, eggs and meat provide variable menaquinones. Leafy greens are foods high in vitamin K overall, mainly K1. Food composition and serving size determine the amount of vitamin present.
What is the side effect of taking vitamin K2?
Digestive symptoms or allergy are possible. The most important risk is an interaction with warfarin and similar anticoagulants, which can alter clotting control. Seek urgent care for unusual bleeding, severe allergy symptoms or other acute concerns.
Vitamin K2 Benefits: Evidence and References
- Australian Government, Eat For Health. Vitamin K: Nutrient Reference Values. Accessed 20 July 2026.
- Mott A, et al. Effect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials. Osteoporosis International. 2019;30:1543–1559. PMID 31076817. doi:10.1007/s00198-019-04949-0.
- Vlasschaert C, et al. Vitamin K supplementation for the prevention of cardiovascular disease: where is the evidence? Nutrients. 2020;12(10):2909. PMID 32977548. doi:10.3390/nu12102909.
- Hasific S, et al. Vitamin K2 and D in patients with aortic valve calcification: a randomised double-blinded clinical trial. Circulation. 2022;145:1387–1397. PMID 35465686. doi:10.1161/CIRCULATIONAHA.121.057008.
- National Institutes of Health, Office of Dietary Supplements. Vitamin K: Health Professional Fact Sheet. Accessed 20 July 2026.
This article provides general educational information, not personalised medical advice. Ask your prescriber before changing vitamin K intake if you use warfarin or another anticoagulant.
