Vitamin K2

Vitamin K2 (menaquinone) is the biological traffic controller for calcium in the body. While vitamin K1 handles blood clotting, K2’s primary role is to activate proteins that determine where calcium is deposited: building it into bones and clearing it from soft tissue like arteries. This makes K2 uniquely important for the dual concern of bone fragility and arterial stiffness, two of the most consequential aging processes.

Arterial Health {#arterial-health}

The most compelling human evidence comes from the Rotterdam Study, a prospective cohort of 4,807 adults followed for up to 10 years. Those in the highest tertile of dietary K2 (menaquinone) intake had 57% lower cardiovascular mortality, 41% lower coronary heart disease risk, and significantly less severe aortic calcification compared to the lowest tertile. Crucially, vitamin K1 intake showed no such association, identifying K2 specifically as the cardioprotective form.

The mechanism centers on matrix Gla protein (MGP), the most potent known inhibitor of vascular calcification. MGP requires K2 for activation; in the absence of sufficient K2, MGP remains inactive and calcification of arterial walls proceeds unchecked. K2 supplementation has been shown to improve arterial elasticity, reduce pulse wave velocity (a marker of arterial stiffness), and slow coronary calcification in several smaller RCTs and prospective studies. A 2021 narrative review confirmed that K2 is underutilized in cardiovascular health despite a mechanistically coherent and clinically supported rationale.

Bone Health {#bone-health}

K2 activates osteocalcin, a bone-matrix protein that anchors calcium into the hydroxyapatite matrix of bone. Without activated osteocalcin, calcium is present in the bloodstream but cannot be efficiently integrated into bone structure. A 2022 systematic review and meta-analysis of 16 RCTs (6,425 participants) found that K2 supplementation maintained and improved lumbar spine bone mineral density (BMD), particularly when combined with vitamin D or calcium. Evidence for fracture reduction alone is less consistent across studies, but the combination of K2 with D3 shows the most reliable benefit. The MK-7 form is preferred for bone and cardiovascular use due to its longer half-life in blood (days vs. hours for MK-4), enabling smaller, once-daily dosing.

Practical Details

MK-7 is the most researched and bioavailable form for supplementation. Typical doses studied in trials range from 90 to 375 mcg/day of MK-7. Natto (fermented soybeans) is the richest dietary source; aged cheese, egg yolks, grass-fed butter, and liver contain smaller amounts. K2 is fat-soluble and should be taken with a fat-containing meal.

The D3+K2 pairing is important: vitamin D3 stimulates calcium absorption from food, and K2 then directs that absorbed calcium toward bones rather than arteries. Many practitioners now recommend taking them together rather than D3 alone.

Caveats

Vitamin K2 interacts with warfarin and other vitamin K antagonist anticoagulants; anyone on these medications should consult a physician before supplementing. The cardiovascular evidence is primarily observational (Rotterdam Study, cohort data) rather than from large RCTs, so the causal link is supported but not as definitively established as for some other supplements.

Calcium Regulation {#calcium-regulation}

Activates proteins that manage where calcium deposits in the body. The evidence and practical framing for this claim are covered in the page narrative above.