Vitamin K2

Vitamin K is a fat-soluble vitamin best known for its role in blood clotting. It also activates a small set of proteins that decide where calcium ends up in your body. Two of those proteins matter most for women. Osteocalcin pulls calcium into bone. Matrix Gla protein keeps calcium out of artery walls. Both proteins only work once vitamin K has carboxylated them.^[1]

Vitamin K2 works closely with vitamin D3 and calcium. D3 raises calcium absorption from the gut. K2 then directs that calcium toward bone rather than soft tissue.^[1] This page covers the difference between K1 and K2, which form is used in supplements and what the recent research shows for women.

Forms of vitamin K

Vitamin K is not a single compound. It is a family of related molecules with different sources and different behaviour in the body.^[1]

Vitamin K1 (phylloquinone) is the form found in leafy greens like kale, spinach, broccoli and Brussels sprouts. It is the dominant dietary form in most Western diets. The liver uses K1 mainly to carboxylate clotting factors.^[1]

Vitamin K2 (menaquinones) is a group of forms labelled MK-4 through MK-13. They come from bacterial fermentation. K2 reaches tissues outside the liver more reliably than K1. Bone and arteries are the main sites where this matters.^[1]

MK-4 has a short half-life of around one to two hours. MK-7 has a half-life of around three days. That longer window means a single daily dose of MK-7 keeps blood levels of vitamin K2 active across the full 24 hours. MK-7 is the most-studied supplement form. This is the form used in nōuxx Cycle Routine.^[1]

Food sources of K2 are limited. Natto (fermented soybeans) is the densest source by a wide margin. Hard cheeses, egg yolks and animal liver contribute smaller amounts. Most women who do not eat natto get very little K2 from food.^[1]

How much you need

The European Food Safety Authority sets adequate intake for vitamin K at 70 µg per day for adult women. This figure is built around blood clotting. Researchers studying bone and cardiovascular outcomes argue the optimal intake for those endpoints sits higher.^[1]

Each phase of nōuxx Cycle Routine delivers 70 µg of vitamin K2 as MK-7. That covers 93% of the daily reference value. The dose is paired with vitamin D3 and calcium so the three nutrients arrive together.

The science on women's health

Bone health

A 2022 systematic review and meta-analysis of 16 randomised controlled trials in 6,425 postmenopausal women found that vitamin K2 supplementation significantly improved lumbar spine bone mineral density. After excluding one heterogeneous study, the pooled fracture incidence was significantly lower in the vitamin K2 group. K2 also reduced undercarboxylated osteocalcin, the marker of K2-deficient bone protein.^[3]

A separate 2022 meta-analysis of nine long-term RCTs in 6,853 postmenopausal women confirmed significant gains in lumbar and forearm BMD with vitamin K2. No serious adverse events were reported.^[4] A 2020 meta-analysis specifically examined K combined with vitamin D. The combination significantly raised total bone mineral density compared with placebo. K2 outperformed K1 in the subgroup analysis.^[5]

Arterial calcification

Matrix Gla protein is the main inhibitor of calcium deposition in arteries. It only works in its carboxylated form, which requires vitamin K2.^[1] The biology is clear. The clinical picture is more mixed.

The 2022 AVADEC trial randomised 365 older adults with established aortic valve calcification to 720 µg MK-7 plus 25 µg vitamin D3 or placebo for two years. Treatment significantly lowered dephosphorylated-undercarboxylated matrix Gla protein. It did not slow progression of aortic valve or coronary artery calcification in this advanced-disease population.^[6] A 2024 review concluded that animal evidence for K2 attenuating calcification is consistent. Strong human outcome data are still missing.^[7] Most ongoing trials are testing earlier-stage prevention rather than late-stage reversal.

One important caution. Women on warfarin or other vitamin K antagonist anticoagulants should not take vitamin K2 supplements without speaking to her prescriber first. K2 directly interferes with how warfarin works and can shift INR.^[7] Direct oral anticoagulants like apixaban and rivaroxaban do not have this interaction.

EU authorised health claims

Under EU law, vitamin K is officially authorised to carry the following health claims:

• Vitamin K contributes to normal blood clotting
• Vitamin K contributes to the maintenance of normal bones^[2]

References

[1] National Institutes of Health, Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. ods.od.nih.gov/factsheets/VitaminK-HealthProfessional

[2] Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. Official Journal of the European Union, 25 May 2012. eur-lex.europa.eu

[3] Ma ML, Ma ZJ, He YL, et al. Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Public Health 2022;10:979649. doi.org/10.3389/fpubh.2022.979649

[4] Zhou M, Han S, Zhang W, Wu D. Efficacy and safety of vitamin K2 for postmenopausal women with osteoporosis at a long-term follow-up: meta-analysis and systematic review. Journal of Bone and Mineral Metabolism 2022;40(5):763-772. doi.org/10.1007/s00774-022-01342-6

[5] Kuang X, Liu C, Guo X, Li K, Deng Q, Li D. The combination effect of vitamin K and vitamin D on human bone quality: a meta-analysis of randomized controlled trials. Food & Function 2020;11(4):3280-3297. doi.org/10.1039/c9fo03063h

[6] Diederichsen ACP, Lindholt JS, Möller S, et al. Vitamin K2 and D in patients with aortic valve calcification: a randomized double-blinded clinical trial. Circulation 2022;145(18):1387-1397. doi.org/10.1161/CIRCULATIONAHA.121.057008

[7] Zhang AJ, Ballantyne CM, Birnbaum Y. Should we recommend vitamin K2 supplement to prevent coronary artery calcification for patients receiving statins and/or warfarin? Cardiovascular Drugs and Therapy 2024;39(6):1585-1588. doi.org/10.1007/s10557-024-07661-2