Vitamin K comes from three places: green plants, animal and fermented foods, and bacteria living in your own gut. Plants produce one form (K1), while bacteria produce a family of related forms (K2). These two types behave differently in your body, get absorbed at different rates, and end up in different organs. Understanding where each form originates helps explain why eating a variety of foods matters for getting enough.
Why Plants Make Vitamin K1
Plants produce vitamin K1 (phylloquinone) inside their chloroplasts, the tiny structures in plant cells that carry out photosynthesis. K1 works as an electron carrier in the photosynthetic machinery, helping convert light energy into chemical energy. This is why the richest sources of K1 are the greenest parts of a plant: the more chlorophyll, the more vitamin K1.
Dark leafy greens and flowering vegetables like broccoli, broccoli raab, and spinach contain over 100 micrograms of K1 per 100 grams. Iceberg lettuce, despite being a common dietary source because people eat so much of it, contains only about 24 micrograms per 100 grams. Roots and tubers like potatoes and carrots contain less than 10 micrograms per 100 grams. Plant oils, particularly soybean and canola oil, also contribute meaningful amounts of K1 because the vitamin is fat-soluble and concentrates in the oil fraction.
K1 from plant foods accounts for the majority of vitamin K in a typical Western diet. But how much you actually absorb depends heavily on what you eat it with. Spinach eaten on its own delivers only about 4% of its K1 into your bloodstream compared to a purified supplement. Adding butter to that spinach triples the absorption. K1 from oil-based sources is absorbed more than three times as efficiently as K1 trapped in a vegetable matrix, because the vitamin needs to dissolve into fat droplets before your intestines can take it up.
Where Vitamin K2 Comes From
Vitamin K2 is actually a family of compounds called menaquinones, each with a slightly different chemical tail. Bacteria produce them as part of their energy metabolism, which is why K2 shows up in two main places: fermented foods and animal products.
The single richest source of K2 on the planet is natto, a Japanese fermented soybean dish. Natto contains nearly 10,000 nanograms per gram of MK-7, a long-chain form of K2. Nothing else comes close. Sauerkraut, another fermented vegetable, contains about 200 times less K2 than natto.
In the Western diet, cheese and other fermented dairy products are the most significant K2 sources. The dominant forms in cheese are MK-9, MK-8, and MK-4, produced by the bacterial cultures used during aging. Aged Gouda contains roughly 145 to 208 nanograms per gram of MK-4, with concentrations increasing as the cheese ages. Münster cheese is notably high in MK-7 at about 84 nanograms per gram. The specific bacteria used in production matter: Emmental cheese contains a unique form (MK-10) because of the particular bacterial strain in its starter culture.
Animal products contain almost exclusively MK-4. Chicken meat has about 101 nanograms per gram, and eel is exceptionally rich at 631 nanograms per gram. Beef and pork meat contain more modest amounts (around 10 to 14 nanograms per gram). Liver is unusual in that it contains some longer-chain menaquinones in addition to MK-4, but liver isn’t widely consumed enough to be a major dietary contributor for most people.
Vitamin K Made Inside Your Body
Bacteria in your large intestine also produce K2 as a byproduct of their normal metabolism. Estimates suggest this internal production covers somewhere between 10% and 50% of your total vitamin K needs, but the exact contribution remains uncertain. The challenge is that most of this bacterial K2 is produced in the colon, where fat absorption is limited, so it’s unclear how much actually makes it into your bloodstream. You can’t rely on gut bacteria alone to meet your vitamin K requirements.
How K1 and K2 Behave Differently
Once absorbed, vitamin K travels through your bloodstream attached to lipoproteins (the same particles that carry cholesterol and other fats). Unlike vitamins A and D, vitamin K has no dedicated carrier protein in the blood, so it hitches a ride on whatever lipoprotein is available.
K1 mostly ends up in the liver, where it activates the proteins responsible for blood clotting. K2 takes a different path. MK-4 travels preferentially to the pancreas and brain, where it may have anti-inflammatory and protective roles. MK-7 heads toward bones and kidneys, where it helps regulate calcium metabolism and vascular health. This division of labor is why eating only leafy greens doesn’t necessarily cover all of vitamin K’s functions in your body.
The two forms also differ dramatically in how well they’re absorbed and how long they last. After eating K2-rich food, blood levels of MK-7 reach concentrations about 10 times higher than K1 levels after eating vegetables. Both are absorbed within about two hours of a meal, but MK-7 stays in circulation for several days, while K1 clears much faster. This longer half-life gives MK-7 more time to reach tissues outside the liver.
How Much You Need
The recommended daily intake for adult men is 120 micrograms, and for adult women it’s 90 micrograms. Children need less, ranging from 30 micrograms for toddlers up to 75 micrograms for teenagers. These recommendations don’t distinguish between K1 and K2, though most research on adequate intake was based on K1’s role in blood clotting.
Meeting these targets is straightforward if you eat green vegetables regularly. A single cup of cooked spinach or broccoli more than covers a full day’s needs. But because absorption from vegetables is relatively poor without dietary fat, pairing greens with olive oil, cheese, nuts, or another fat source makes a real difference. People who eat very low-fat diets or who have conditions affecting fat absorption (like celiac disease or pancreatic insufficiency) are at higher risk of falling short.
Synthetic Vitamin K
There is a third, synthetic form called vitamin K3 (menadione). It’s a simpler molecule that lacks the side chain found in K1 and K2. While it’s used as a supplement in livestock feed, K3 was withdrawn from human use because it can cause a type of anemia where red blood cells break down, along with liver toxicity. Supplements for people use either K1 or K2 forms instead. Interestingly, the MK-4 found in animal meat partly originates from menadione added to animal feed, which the animals then convert into the natural K2 form in their own tissues.