💊 What it does
Vitamin K2 (menaquinone) directs calcium to bones and teeth and away from soft tissues and arteries, working in close partnership with vitamin D3. It activates two key proteins: osteocalcin (which anchors calcium into bone matrix) and matrix Gla protein (which prevents calcium from depositing in artery walls). K2 is increasingly recognised as an important factor in cardiovascular health and bone density, particularly in populations supplementing vitamin D.
👤 Who needs it
Anyone taking long-term vitamin D3 supplements — D3 increases calcium absorption significantly, and K2 is needed to ensure that calcium goes to bones rather than arteries. Post-menopausal women concerned about bone density. People with risk factors for cardiovascular calcification. Those who do not eat fermented foods regularly (natto, certain aged cheeses are the main K2 food sources).
🥦 Food sources first
Natto (fermented soya beans) is by far the richest source of MK-7 — one small serving provides several hundred micrograms. Most people in the UK do not eat natto. Smaller amounts of K2 (mainly MK-4) are found in certain cheeses (Gouda, Brie, Edam) and butter from grass-fed cows. Plant-based eaters have very limited dietary K2 from food.
🗓 When to supplement
When supplementing vitamin D3 long-term, particularly at doses of 25 µg (1,000 IU) or above. When bone density is a concern. When cardiovascular calcification is a risk factor.
🏷 Best form to look for
MK-7 (menaquinone-7) is the long-acting form — it stays active in the body for days, giving consistent coverage. MK-4 is the shorter-acting form, requiring multiple daily doses. MK-7 derived from natto fermentation is the most widely studied plant-based form.
⏰ When to take it
Take with a meal containing fat — vitamin K2 is fat-soluble. Evening with dinner works well for most people.