Vitamin K2: What You Need to Know Before Buying
Vitamin K2 is a fat-soluble vitamin often mentioned alongside vitamin D3. But K2 is important in its own right: without it, the body cannot properly direct calcium. This guide explains the differences between the two main forms, evidence-based doses, and who particularly needs K2.
Important warning: Vitamin K2 can interact with anticoagulants (e.g. warfarin). If you take blood-thinning medications, consult your doctor BEFORE starting K2.
Who Is This Guide For?
- People taking vitamin D3 who want to know whether adding K2 is necessary
- Those who want to support bone health with evidence-based supplementation
- Anyone confused about the difference between MK-4 and MK-7
- People looking for K2 products in Estonia
TL;DR — Key Takeaways
- K2 comes in two main forms: MK-4 (synthetic, short half-life) and MK-7 (natural, long half-life)
- MK-7 is preferred for daily use: effective at 90–200 μg/day
- MK-4 is effective but requires much higher doses (45 mg/day) given 3x daily, as used in Japanese clinical trials
- K2 combined with D3 directs calcium to bones, not arteries
- Buy all-trans MK-7 (not cis), naturally fermented (natto-based)
- Critical: K2 may affect vitamin K antagonists (warfarin) — speak to your doctor
Background: Why K2 Matters
Two Roles of Vitamin K
- K1 (phylloquinone) — found in green leafy vegetables; needed for blood clotting
- K2 (menaquinone) — found in fermented foods and animal sources; plays a key role in calcium metabolism outside the liver
K2 activates two important proteins:
1. Osteocalcin — binds calcium into bone matrix → stronger bones
2. Matrix Gla-protein (MGP) — prevents calcium deposits in arteries → lower arterial calcification risk
Why K2 Is Connected to D3
D3 increases calcium absorption in the intestine — a good thing. But the increased calcium in blood needs to be directed. K2 ensures calcium goes to bones, not arterial walls. The D3+K2 combination is therefore biologically justified.
Geleijnse et al. (2004) in the Rotterdam Study found that higher dietary K2 intake was associated with lower cardiovascular disease risk.
MK-4 vs MK-7: Which to Choose?
MK-4 (menaquinone-4)
- Origin: Synthetic; found in animal products (meat, eggs)
- Half-life: Short (~1–2 hours) — requires multiple daily doses
- Effective dose: 45 mg (milligrams, not micrograms!) 3x daily as used in Japanese studies
- Use: Mainly in therapeutic context (Japan, osteoporosis treatment)
- In supplements: Typically at 100–1000 μg doses, which lack proven efficacy
MK-7 (menaquinone-7)
- Origin: Natural; produced by fermentation (natto, some cheeses, biotechnological fermentation)
- Half-life: Long (~72 hours) — one daily dose is sufficient
- Effective dose: 90–200 μg/day
- Research: Knapen et al. (2013) showed MK-7 180 μg/day improved bone strength over 3 years; Geleijnse et al. (2004) linked dietary K2 to cardiovascular health
- Recommended: Better choice for most consumers for daily use
How to Buy Quality K2 MK-7
What to Look For
1. All-trans MK-7 — not cis-MK-7. The biologically active form is all-trans. The cis-isomer is inactive. Check the label or manufacturer documentation.
2. Naturally fermented — MK-7 from natto fermentation (Bacillus subtilis var. natto) is the most studied. Look for "naturally fermented" or "natto-derived" on the label.
3. Third-party tested — NSF International, USP, Informed Sport, or similar certification.
4. Clean ingredients — avoid unnecessary fillers. As a fat-soluble vitamin, K2 absorbs better with food (especially fatty food).
5. Dose — 90–200 μg MK-7 per day is the evidence-based range for adults.
Dosage and Use
| Goal | Recommended MK-7 dose | Notes |
|---|---|---|
| General health, bone support | 90–120 μg/day | EFSA safe upper level: 600 μg/day |
| Combined with D3 | 90–200 μg/day | Appropriate for most D3 users |
| Medical prescription | As directed | Higher doses in osteoporosis treatment |
Take with a fatty meal — K2 is fat-soluble and absorbs significantly better with dietary fat.
Drug Interactions: Who Should Be Cautious?
CRITICAL: Anticoagulants
Vitamin K affects blood clotting. If you take warfarin, acenocoumarol, or other vitamin K antagonists, adding K2 may reduce their effectiveness and destabilise INR levels.
Important clarification: While K1 interaction with warfarin is well-established, K2 interaction is less clear — some studies suggest MK-7's long half-life may affect anticoagulant activity.
Rule: If you take blood-thinning medications, speak to your doctor BEFORE starting K2 supplementation.
Other Interactions
- Some antibiotics can disrupt K2 production in the gut — short-term supplementation may be warranted during antibiotic courses
Common Mistakes When Buying K2
Mistake 1: Buying cis-MK-7 thinking it is the same
The cis-isomer is not biologically active. Verify the product contains all-trans MK-7.
Mistake 2: Low-dose MK-4 products
Typical 100–500 μg MK-4 supplements have not demonstrated efficacy. MK-4 is effective only at 45 mg 3x daily as used in clinical trials.
Mistake 3: Taking K2 with anticoagulants without medical consultation
This is a serious risk. Always consult your doctor first.
Mistake 4: Taking K2 without fat
Fat-soluble vitamins absorb poorly without dietary fat. Take with a meal.
Frequently Asked Questions
Does K2 replace K1?
No, they serve different purposes. K1 is for blood clotting; K2 is for calcium metabolism outside the liver. Both are important.
Is K2 suitable for vegans?
Most K2 MK-7 is produced by fermentation — usually without animal products. However, always check the capsule is not gelatine.
Does K2 help with osteoporosis?
Knapen et al. (2013) showed MK-7 180 μg/day over 3 years had a positive effect on bone strength. This is promising, but K2 does not replace doctor-prescribed osteoporosis treatment.
When to take K2 — morning or evening?
Most important is to take it with a fatty meal. Morning or lunch works well. With MK-7's long half-life, timing is less critical.
How much K2 is in food?
Natto (Japanese fermented soya) is among the richest sources — but not a common food in Estonia. Hard cheeses (Gouda, Edam) contain moderate K2. Most Estonians have low dietary K2 intake.
Local Angle — K2 in Estonia
MaxFit.ee offers vitamin K2 products — look for all-trans MK-7 with fermented origin. In Estonia, dietary K2 intake is low since natto is not a local food. Supplementation is therefore sensible, especially when combined with D3.
Prices: K2 MK-7 supplements typically cost €10–25 per package (2–3 months supply). This is affordable, considering the synergistic benefits when combining with D3 supplementation.
References
1. Geleijnse JM, Vermeer C, Grobbee DE, et al. (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.
2. Knapen MH, Drummen NE, Smit E, et al. (2013). Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, 24(9), 2499–2507.
3. Theuwissen E, Smit E, Vermeer C. (2012). The role of vitamin K in soft-tissue calcification. Advances in Nutrition, 3(2), 166–173.
4. Sato T, Inaba N, Yamashita T. (2020). MK-7 and its effects on bone quality and strength. Nutrients, 12(4), 965.
5. Vermeer C. (2012). Vitamin K: the effect on health beyond coagulation — an overview. Food & Nutrition Research, 56, 5329.
Summary and Buying Checklist
Vitamin K2 is an important but underappreciated nutrient, especially alongside vitamin D3. Daily use of all-trans MK-7 at 90–200 μg is the evidence-based choice.
Buying checklist:
1. Form: all-trans MK-7 (not cis, not low-dose MK-4)
2. Origin: naturally fermented (natto-based)
3. Dose: 90–200 μg/day
4. Third-party certified
5. Anticoagulants: SPEAK TO YOUR DOCTOR before starting
See also:
- Vitamin D 4000 IU: Who Needs It and When
- D3, K2, and Omega-3: Why Take Them Together and How to Dose
- Vitamin D Reference Values: What the Numbers Mean
See also:
