Vitamin K1 vs K2: Two Different Nutrients Wearing the Same Name
"Vitamin K" is often talked about as a single nutrient, but it actually describes a family of related compounds that behave quite differently in the body. The two that matter for supplementation — K1 and K2 — come from different food sources, are absorbed and used differently, and support different functions. If you've read our post on Vitamin D3 and K2, this article goes one level deeper into Vitamin K itself.
What Vitamin K Does, Broadly
Vitamin K is a fat-soluble vitamin with two EU-approved health claims: normal blood clotting, and maintenance of normal bones. Both forms of Vitamin K contribute to these functions, but the balance of evidence and the practical mechanism differs meaningfully between K1 and K2.
Vitamin K1 (Phylloquinone)
Vitamin K1 is the primary dietary form of Vitamin K and the one most people get in reasonable amounts without trying — it's abundant in green leafy vegetables: kale, spinach, broccoli, and Brussels sprouts. K1 is the form most directly associated with normal blood clotting, since it's used heavily by the liver to produce clotting factors.
Because leafy greens are a relatively common part of most UK diets (even if not eaten daily by everyone), outright K1 deficiency is uncommon in adults without an underlying absorption issue or a specific reason for concern, such as long-term antibiotic use or malabsorption conditions.
Vitamin K2 (Menaquinones, Including MK-7)
Vitamin K2 refers to a group of compounds called menaquinones, of which MK-7 is the form most commonly used in supplements due to its longer half-life in the bloodstream. K2 occurs naturally in fermented foods (natto, in particular, though this isn't a significant part of typical UK diets), certain hard cheeses, and egg yolks — sources most people consume far less consistently than leafy greens.
K2's more specifically studied role is activating osteocalcin and matrix Gla-protein (MGP), two proteins involved in directing calcium into bone and away from soft tissue such as arterial walls. This is the mechanism covered in more depth in our Vitamin D3 + K2 article — K2's role becomes particularly relevant for anyone supplementing calcium or higher-dose Vitamin D3 over the long term.
Why the Distinction Gets Missed
Many older or budget multivitamins include only Vitamin K1, sometimes simply labelled "Vitamin K," without specifying the form — a legacy of K1 being the form originally studied and required for its blood-clotting role. This can leave the K2-specific bone and calcium-related functions unaddressed even in someone who believes they're already covering their Vitamin K needs.
Conversely, K1 intake from diet is generally more reliable than K2 intake for most people, given how much more common leafy greens are in the average UK diet than fermented foods or specific cheeses. This is why a combined K1 + K2 formula, rather than either form alone, gives more complete coverage than relying on the assumption that "Vitamin K" on a label means you're getting both.
Vitamin K1 vs K2 at a Glance
| Vitamin K1 (Phylloquinone) | Vitamin K2 (MK-7) | |
|---|---|---|
| Main food sources | Green leafy vegetables | Fermented foods, hard cheese, egg yolks |
| Primary role | Blood clotting | Directing calcium to bone, away from soft tissue |
| Typical dietary adequacy in UK | Reasonably common | Often genuinely low |
| Half-life in blood | Short | Longer (MK-7 specifically) |
Who Should Pay Particular Attention
- Anyone taking calcium or higher-dose Vitamin D3 supplements long-term — K2's calcium-directing role becomes more relevant the more calcium is circulating
- Postmenopausal women, given accelerated bone density changes
- Those eating little to no dairy, eggs, or fermented food — the main K2 sources
- Anyone on long-term antibiotics, which can reduce the gut bacteria that contribute to some Vitamin K production
Anyone on anticoagulant medication such as warfarin should speak to a GP before starting any Vitamin K supplement, in either form, as Vitamin K directly interacts with how these medications work.
What Health Leads Offers
Both Health Leads Vitamin K products combine K1 (Phylloquinone) with K2 (as MK-7) in a single daily capsule — Vitamin K Complex 150mcg (K1 100mcg / K2 50mcg) for standard daily use, or Vitamin K Complex 450mcg High Strength (K1 300mcg / K2 150mcg) for those wanting a more concentrated daily dose.
The Bottom Line
K1 and K2 share a name but do meaningfully different jobs — K1 for blood clotting, K2 for directing calcium into bone rather than soft tissue. Most people get reasonable K1 from diet without trying; K2 is the form far more likely to be genuinely low, particularly for anyone not regularly eating fermented foods, hard cheese, or egg yolks. A combined formula covers both rather than assuming one implies the other.
Health Leads Vitamin K Complex — K1 (Phylloquinone) and K2 (MK-7) combined, available at 150mcg and 450mcg total strength. No magnesium stearate, no artificial additives. Made in Wales. ISO accredited. Additive-free since 1998. View product →