Why Plant-Based Diets May Fall Short of Vitamin K
Vitamin K for vegans encompasses an important distinction that is often overlooked: vitamin K is not a single compound but two main forms with different food sources, different functions, and importantly different availability on plant-based diets.
Vitamin K1 (phylloquinone) is found abundantly in dark leafy green vegetables – kale, spinach, broccoli, Brussels sprouts, and similar. Vegans who eat plenty of greens are generally not at risk of K1 deficiency. K1 is primarily involved in blood coagulation.
Vitamin K2 (menaquinones, particularly MK-4 and MK-7) is where the challenge lies for vegans. K2 is found primarily in fermented dairy products (especially cheese), egg yolk, and some fermented soy products. It has distinct functions beyond blood clotting, particularly in bone metabolism (activating osteocalcin) and cardiovascular health (activating matrix Gla protein, which prevents arterial calcification).
The dietary landscape of vitamin K2 for vegans is genuinely narrow. Most plant foods provide virtually no K2. The main plant-based exception is natto (a Japanese fermented soybean product), which contains very high amounts of MK-7 – but it is not widely consumed in Estonia or most of Europe, and its strong taste makes daily consumption unrealistic for many.
A prospective study found that dietary vitamin K2 (particularly MK-7 and MK-8 from fermented foods) was inversely associated with coronary heart disease risk, while K1 showed no such association (Geleijnse et al., 2004). This suggests that K2 has functions distinct from K1 and may be the more physiologically important form for long-term health outcomes.
Vegan-Friendly Vitamin K Sources
K1 sources (good availability on plant-based diets):
- Kale, collard greens, spinach
- Broccoli, Brussels sprouts
- Parsley, coriander
- Green tea leaves
K2 sources (limited availability on plant-based diets):
- Natto – very high MK-7 content, but rarely consumed in Estonia
- Some plant-based fermented foods may contain small amounts
- Sauerkraut and other fermented vegetables – minimal K2
The practical takeaway is that vegans eating diverse greens will meet their K1 needs, but K2 intake will be substantially lower than in omnivores or dairy-consuming vegetarians.
Dose Targets
Dietary reference values for vitamin K do not differentiate K1 from K2. For total vitamin K, adult Adequate Intake is in the range of 70–120 mcg/day in most European reference frameworks, depending on age and sex.
For K2 specifically (MK-7 form), available supplement doses typically range from around 45 mcg to 200 mcg per day. Research on optimal K2 supplementation for bone and cardiovascular outcomes has used a range of doses. A randomised trial found that MK-7 supplementation improved bone mineral density and reduced undercarboxylated osteocalcin (a marker of vitamin K deficiency in bone) in postmenopausal women (Knapen et al., 2013).
At maxfit.ee, NOW Vitamin K-2 (MK7) 100mcg 60 veg. caps. and OstroVit Vitamin K2 200 Natto MK-7 90tabs are available. Products combining D3 and K2 – such as OstroVit Vitamin D3 + K2 90 tabs and NOW Vitamin D-3 & K-2 120caps – are also available in the vitamin K category.
What to Combine with Vitamin K
Vitamin D: The synergy between vitamins D and K2 in bone and cardiovascular health is well-established. Vitamin D promotes calcium absorption, while K2 directs calcium to bone (via osteocalcin) and away from soft tissues (via matrix Gla protein). Supplementing vitamin D without K2 may not deliver the full benefit of vitamin D for bone quality. Vegans who supplement vitamin D (highly recommended in northern latitudes) should consider co-supplementing with K2.
Calcium: All three work together – adequate calcium is the substrate, vitamin D improves absorption, and K2 ensures proper deposition. Vegans may have lower calcium intake than dairy consumers, making the K2 role in directing calcium to the right tissues particularly relevant.
Dietary fat: Vitamin K is fat-soluble. Take K supplements with a fat-containing meal for optimal absorption.
Choosing a Vegan K2 Supplement
Most vitamin K2 supplements are derived from natto fermentation (bacteria-produced MK-7) and are inherently vegan. However:
- Check capsule material – gelatin capsules (bovine/porcine) are not vegan; look for HPMC or vegetarian-labelled capsules
- MK-7 is preferred over MK-4 for supplementation – MK-7 has a longer half-life and may require less frequent dosing
- Avoid very high doses without need – there is no established toxicity for vitamin K at typical supplement doses, but moderation is sensible
- If on anticoagulant medication (e.g., warfarin): vitamin K supplements of any kind can interfere with anticoagulation therapy. This is a genuine contraindication – consult your physician before using K supplements
Bottom Line
Vitamin K for vegans is a two-part story: K1 from greens is generally adequate, but K2 from fermented animal products is the gap. For vegans not consuming natto regularly, a K2 (MK-7) supplement is a highly rational addition, particularly when combined with vitamin D supplementation. The K2-D3 combination is well-supported for bone and cardiovascular health and is readily available at maxfit.ee.
References
Geleijnse, J. M., Vermeer, C., Grobbee, D. E., Schurgers, L. J., Knapen, M. H., van der Meer, I. M., Hofman, A., & Witteman, J. C. (2004). Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. Journal of Nutrition, 134(11), 3100–3105. https://pubmed.ncbi.nlm.nih.gov/15514282/
Knapen, M. H., Drummen, N. E., Smit, E., Vermeer, C., & Theuwissen, E. (2013). Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, 24(9), 2499–2507. https://pubmed.ncbi.nlm.nih.gov/23525894/
Vermeer, C. (2012). Vitamin K: the effect on health beyond coagulation - an overview. Food & Nutrition Research, 56, 5329. https://pubmed.ncbi.nlm.nih.gov/22489224/
FAQ
Do vegans get enough vitamin K from leafy greens?
Vegans who eat plenty of dark green leafy vegetables will generally meet their vitamin K1 needs. However, K1 and K2 have different functions, and K2 – important for bone metabolism and cardiovascular health – is largely absent from plant foods (with natto as the main exception). A K2 supplement is worth considering for vegans not regularly consuming natto.
Can I take vitamin K2 if I am on blood thinners?
No – this is an important contraindication. Vitamin K interferes with anticoagulant medications such as warfarin by opposing their mechanism of action. If you are on anticoagulants, do not take vitamin K supplements without explicit guidance from your prescribing physician. This is a clinical safety requirement, not a general caution.
What is the difference between K2 MK-4 and MK-7?
MK-4 and MK-7 are both forms of vitamin K2 (menaquinones) but differ in their chain length and pharmacokinetics. MK-7 has a longer half-life in the body, meaning that it remains active for longer and can be supplemented less frequently (once daily is sufficient). MK-4 requires multiple daily doses to maintain blood levels. For supplementation purposes, MK-7 (typically derived from natto fermentation) is generally preferred.
