Vitamin K2 (Menaquinone)
The calcium-directing vitamin that keeps calcium in bones and out of arteries
Also known as: Menaquinone-7 • MK-7 • Menaquinone-4 • MK-4 • Vitamin K2
Overview
Vitamin K2 is a group of fat-soluble vitamins (menaquinones) that activate calcium-regulating proteins in the body. While vitamin K1 (phylloquinone) primarily supports blood clotting, K2 activates osteocalcin (which deposits calcium into bones) and matrix GLA protein (which prevents calcium from depositing in arteries). This dual action makes K2 uniquely important for both bone health and cardiovascular protection. The two most important forms are MK-4 (short-acting, found in animal foods) and MK-7 (long-acting, from fermented foods like natto). K2 deficiency is widespread because modern diets are low in fermented foods and grass-fed animal products. K2 is especially important when supplementing with vitamin D3 and calcium, as D3 increases calcium absorption but K2 directs where that calcium goes.
Key Benefits
Bone Health & Osteoporosis Prevention
K2 activates osteocalcin, the protein that binds calcium to bone matrix. The Rotterdam Study found that high K2 intake reduced hip fracture risk by 50%. MK-4 at 45mg/day is an approved osteoporosis treatment in Japan. MK-7 at 180mcg/day improved bone mineral density in postmenopausal women.
Arterial Calcification Prevention
K2 activates matrix GLA protein (MGP), the most potent inhibitor of vascular calcification. The Rotterdam Study found high K2 intake reduced cardiovascular mortality by 50% and aortic calcification by 50%. K2 may even reverse existing arterial calcification.
Synergy with Vitamin D3
Vitamin D3 increases calcium absorption from the gut, but without K2, that calcium may deposit in arteries instead of bones. K2 directs D3-absorbed calcium to bones. This is why D3 + K2 is considered the optimal combination.
Dental Health
K2 activates osteocalcin in dentin (the layer beneath tooth enamel), supporting tooth mineralization and potentially reducing cavity formation. Weston Price's historical research identified K2 (which he called 'Activator X') as crucial for dental health in traditional diets.
Dosage & How to Take
For MK-7: 100-200mcg daily. For MK-4: 1-45mg daily (MK-4 has a much shorter half-life and requires higher doses). MK-7 is preferred for daily supplementation due to its 72-hour half-life vs MK-4's 6-8 hours.
| Purpose | Dose | Notes |
|---|---|---|
| General health with D3 | 100-200 mcg MK-7 daily | Standard dose when taking vitamin D3 |
| Osteoporosis prevention | 180 mcg MK-7 daily | Based on 3-year clinical trial showing BMD improvement |
| Osteoporosis treatment (Japan) | 45 mg MK-4 daily | Prescription dose in Japan. Much higher than MK-7. |
| Cardiovascular protection | 180-360 mcg MK-7 daily | Higher doses for arterial calcification |
Best Time to Take
Take with the largest fat-containing meal of the day. K2 is fat-soluble and requires dietary fat for absorption.
With or Without Food
Always take with food containing fat. Absorption is significantly reduced without dietary fat.
Forms & Bioavailability
| Form | Absorption | Best For | Notes |
|---|---|---|---|
| MK-7 (Menaquinone-7) | High | Daily supplementation | 72-hour half-life. Low dose needed. Derived from natto fermentation. Most popular form. |
| MK-4 (Menaquinone-4) | Moderate | Therapeutic doses, bone treatment | 6-8 hour half-life. Requires much higher doses (mg vs mcg). Used in Japanese osteoporosis treatment. |
| MK-7 + MK-4 Combination | High | Comprehensive K2 coverage | Some products combine both forms for immediate and sustained activity. |
Side Effects & Safety
Common
- No known side effects at recommended doses
- No known toxicity level (no Upper Limit established)
Rare
- Theoretical concern with blood clotting in those on anticoagulants
Contraindications
- Warfarin users — K2 can counteract warfarin's anticoagulant effect (consult doctor)
- Other anticoagulants — discuss with doctor before supplementing
Interactions
Vitamin K (all forms) counteracts warfarin by activating clotting factors. K2 supplementation can destabilize INR. Must consult doctor.
Synergistic — D3 increases calcium absorption, K2 directs calcium to bones. Always combine.
K2 ensures supplemental calcium goes to bones, not arteries. Important safety combination.
Scientific Research
Rotterdam Study (K2 and Heart Disease)
High dietary K2 intake was associated with 50% reduction in cardiovascular mortality and 50% reduction in aortic calcification over 7-10 years
MK-7 and Bone Health
180mcg MK-7 daily for 3 years improved bone mineral density and bone strength in postmenopausal women
MK-7 and Arterial Stiffness
180mcg MK-7 daily for 3 years improved arterial stiffness, especially in women with high baseline stiffness
Food Sources
Frequently Asked Questions
Medical Disclaimer
This content is for educational and informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional before starting any supplement regimen, especially if you have pre-existing health conditions or are taking medications. The statements on this page have not been evaluated by the Food and Drug Administration.