Vitamin K1
The one from leaves. Absorbed far better from a tablet than from the spinach it came from.
Vitamin K1, phylloquinone, is the form in green leafy vegetables and the main one in most diets. The absorption gap is the number worth carrying: free phylloquinone from a tablet absorbs at roughly 80%, while the body takes up only about 4 to 17% as much from spinach, because in a leaf it is bound tightly into the chloroplast. Fat in the same meal improves it either way. EFSA sets an adequate intake of 1 microgram per kilogram of body weight a day, which comes to 70 micrograms for adults, and UK COMA landed on the same per-kilogram figure in 1991. There is no upper limit, in the UK, EU or US, because vitamin K has not shown toxicity from food or supplements. The one interaction that genuinely matters is warfarin and the related anticoagulants, where the goal is a steady intake rather than a low one, since it is the swings that move your INR.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| RDA | Upper limit | Source |
|---|---|---|
| 70 mcg | No UL set | UK SACN DRVs (1991) -- vitamin K adequate intake ~1 mcg/kg/day; 70 mcg/day used for 70 kg reference adult. No SACN or EFSA numerical UL established. |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| Phylloquinone (plant K1) | Typical | With food | Either | Strong |
| Menaquinone MK-4 (animal K2) | Higher | With food | Split dose | Likely |
| Menaquinone MK-7 (fermented K2) | Higher | With food | Either | Strong |
How it pairs with other supplements
Works well with
Vitamin D3 and K1 (phylloquinone) work together for calcium handling: D3 increases intestinal calcium absorption, K1 activates gamma-carboxylation of osteocalcin and matrix Gla protein (MGP) to direct calcium to bone rather than soft tissue. Often co-supplemented in bone health stacks.
Stack Almanac tracks K1 as fat-soluble and pairs it with vitamin D3 for calcium handling, and it keeps your daily total steady on the record, which is the thing that matters if you are on an anticoagulant.
Track your Vitamin K1 in Stack Almanac
Last reviewed: 2026-05-25. Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.