Vitamin K

Vitamin K

Vitamin K is a fat-soluble vitamin with two main jobs: blood clotting and bone health. The clotting role is the more immediately critical one — vitamin K is essential for the production of several proteins the body uses to form clots, and severe deficiency produces a situation where bleeding doesn’t stop properly. That level of deficiency is rare in healthy adults but more of a concern in newborns, which is why vitamin K injections at birth are standard medical practice.

The bone health role is less widely known but genuinely important. Vitamin K activates proteins that regulate where calcium gets deposited in the body — directing it toward bones and teeth rather than soft tissue and blood vessels. This is also why vitamin K becomes particularly relevant when supplementing vitamin D at higher doses. Vitamin D increases calcium absorption. Vitamin K helps make sure that calcium ends up where it belongs. The two work as a team in a way that’s worth understanding if you’re supplementing either.

Vitamin K exists in two main forms. K1 is found in leafy greens and is the primary dietary form for most people. K2 is found in fermented foods and some animal products — particularly a Japanese fermented soybean dish called natto, which contains more K2 than virtually any other food, and grass-fed dairy and egg yolks in smaller amounts. K2 is thought to be particularly relevant for the calcium-directing function, and it’s the form most commonly found in supplements.

Deficiency in healthy adults eating vegetables is uncommon. People on blood-thinning medications like warfarin need to be consistent about their vitamin K intake rather than avoiding it — sudden large changes in intake affect how the medication works.

Reference Card

Vitamin type: Fat-soluble Pillar: Nourish

What it does for you

  • Essential for blood clotting — without it, wounds don’t close properly
  • Activates proteins that direct calcium to bones and teeth rather than soft tissue
  • Supports bone density and cardiovascular health over time

Two forms

  • Vitamin K1 — found in leafy greens; the primary dietary form for most people
  • Vitamin K2 — found in fermented foods and some animal products; particularly relevant for calcium regulation and bone health

Where to get it

  • K1 — kale, spinach, collard greens, broccoli, Brussels sprouts, lettuce
  • K2 — natto, grass-fed dairy, egg yolks, aged cheese, chicken

Considerations

  • Fat-soluble — requires fat present at the same meal for absorption; eat leafy greens with olive oil or another fat source
  • Works closely with vitamin D — particularly relevant when supplementing vitamin D at higher doses
  • People on blood-thinning medications should keep vitamin K intake consistent rather than dramatically increasing or decreasing it
  • Deficiency is uncommon in people eating regular vegetables

Signs your intake might be low

  • Easy bruising
  • Wounds that take longer than expected to stop bleeding
  • Bone density issues over time

Common myths

  • People on blood thinners should avoid vitamin K — consistency matters more than avoidance; dramatic swings in intake are the issue, not vitamin K itself
  • K1 and K2 are interchangeable — they have overlapping but distinct roles; K2 in particular is harder to get from a typical Western diet and more specifically relevant for calcium regulation
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