Vitamin K is found in two main forms across a wide range of foods. The richest sources are dark leafy greens like kale, spinach, and collard greens, which can deliver several hundred micrograms in a single serving. You’ll also find it in certain fermented foods, dairy products, and meats. Adults need 90 to 120 mcg per day, and a single cup of cooked spinach can exceed that amount several times over.
The Two Forms of Vitamin K
Vitamin K comes in two main types, and they show up in different foods. K1 is found almost exclusively in plants, especially green vegetables. K2 is produced by bacteria during fermentation and is also present in animal products like egg yolks, cheese, and organ meats. Both forms help your body with the same essential jobs, but K2 tends to stay in your system longer.
Best Sources of Vitamin K1
Green leafy vegetables are by far the most concentrated sources. The darker the leaf, the more vitamin K1 it typically contains. Here are the standout foods:
- Kale: one of the richest sources, with a single cooked cup providing well over 500 mcg
- Spinach: similarly high, delivering several hundred mcg per cooked cup
- Collard greens: comparable to kale and spinach
- Swiss chard: another powerhouse green
- Turnip greens and mustard greens: both exceptionally high
- Broccoli and Brussels sprouts: solid sources, though lower than leafy greens
- Asparagus: a moderate source
Green vegetables dominate the list because vitamin K1 is directly involved in photosynthesis. The chlorophyll-rich parts of a plant are where it concentrates. Cooking these vegetables doesn’t destroy much of the vitamin K, and in some cases it makes the nutrient easier to absorb because heat breaks down the plant cell walls.
Certain plant oils, particularly soybean and canola oil, also contribute meaningful amounts. If you cook regularly with these oils, they can add to your daily intake without you thinking about it.
Best Sources of Vitamin K2
Vitamin K2 is harder to get from a typical Western diet. The single most concentrated source in the world is natto, a traditional Japanese food made from soybeans fermented with a specific strain of bacteria. Natto contains over 880 mcg of K2 per 100 grams, roughly 124 times the amount found in unfermented soybeans. Its sticky texture and strong flavor make it an acquired taste, but nutritionally it’s in a class of its own.
Beyond natto, other sources of K2 include:
- Hard and soft cheeses: particularly aged varieties like Gouda and Brie
- Egg yolks: a modest but consistent source
- Chicken and beef liver: organ meats are among the best animal sources
- Chicken thighs and other dark meat: contain small amounts
- Fermented foods: sauerkraut and certain fermented dairy products contain varying levels depending on the bacterial strains involved
The gut bacteria in your intestines also produce some K2, though how much of that your body actually absorbs and uses remains unclear.
Why Your Body Needs Vitamin K
Vitamin K’s most critical job is helping your blood clot. It activates several proteins in the clotting cascade by enabling them to bind calcium, a step that’s essential for wounds to stop bleeding. Without enough vitamin K, these proteins can’t function properly, which leads to excessive bleeding and easy bruising.
It also plays a role in bone health. Vitamin K activates a protein called osteocalcin, which is needed for the growth and maturation of the calcium crystals that give bones their strength. Deficiency has been linked to osteoporosis, though the full relationship between vitamin K intake and bone density is still being studied.
There’s been interest in whether K2 specifically can prevent calcium from building up in arteries. A randomized trial published in Circulation tested high-dose K2 supplements in men with existing aortic valve calcification over two years and found no significant difference in calcification progression compared to placebo. So while the theory is biologically plausible, supplementation hasn’t proven to reverse or slow arterial calcification in clinical trials.
How Much You Need
The recommended daily intake set by the National Institutes of Health is 120 mcg for adult men and 90 mcg for adult women. Pregnant and breastfeeding women need 90 mcg as well. Children’s needs are lower, ranging from 30 mcg at age 1 to 75 mcg for teenagers.
These numbers are easy to hit if you eat green vegetables regularly. A single serving of kale, spinach, or broccoli at dinner can cover your entire day. People who eat very few vegetables or follow highly restrictive diets are the most likely to fall short. No upper limit has been set for vitamin K from food or supplements because toxicity from natural sources hasn’t been documented.
Vitamin K Absorbs Better With Fat
Vitamin K is fat-soluble, meaning your body absorbs it much more efficiently when you eat it alongside some dietary fat. A salad dressed with olive oil or vegetables sautéed in butter will deliver more usable vitamin K than the same vegetables eaten plain. This is true for both K1 and K2. You don’t need a lot of fat for this effect, just enough to trigger the digestive process that pulls fat-soluble vitamins into your bloodstream.
Signs of Deficiency
Vitamin K deficiency is uncommon in healthy adults who eat a varied diet, but when it occurs, the main symptom is abnormal bleeding. This can show up as easy bruising, small red or purple spots on the skin, slow-to-stop bleeding from cuts, or blood in urine or stool. The underlying issue is that your blood-clotting proteins can’t activate without adequate vitamin K.
Newborns are particularly vulnerable because they’re born with very low vitamin K stores and breast milk provides only small amounts. This is why hospitals routinely give infants a vitamin K injection shortly after birth, to prevent a condition called hemorrhagic disease of the newborn, which can cause dangerous internal bleeding in the first weeks or months of life.
Vitamin K and Blood Thinners
If you take a blood thinner like warfarin, vitamin K intake matters more than it does for most people. Warfarin works by blocking vitamin K’s role in the clotting process, so eating significantly more or less vitamin K than usual can make the medication either less effective or too effective. The key is consistency: you don’t need to avoid green vegetables, but you should eat roughly the same amount from day to day and week to week. Sudden changes, like adding a large daily kale smoothie or cutting out greens entirely, can throw off your medication’s balance.