Vitamin K and vitamin K2 are not the same thing. “Vitamin K” is an umbrella term that covers a whole family of related compounds, and K2 is one branch of that family. The other major branch is vitamin K1. Both play essential roles in your body, but they come from different sources, travel to different tissues, and do somewhat different jobs once they get there.
How K1 and K2 Relate
Think of “vitamin K” the way you might think of “vitamin B.” It’s a category, not a single molecule. Within that category, there are two naturally occurring forms: vitamin K1 (also called phylloquinone) and vitamin K2 (a group of compounds collectively called menaquinones). They share the same core chemical structure but differ in the length and shape of a molecular side chain, and that small difference changes how your body handles each one.
K1 is made by plants. It’s the form you get from leafy greens like spinach, kale, and broccoli, and it accounts for the majority of vitamin K in a typical diet. K2, on the other hand, comes primarily from animal products and fermented foods. Your gut bacteria also produce some K2, potentially covering 10 to 50 percent of your total vitamin K needs, though the exact contribution is still uncertain.
They Work in Different Parts of Your Body
Both K1 and K2 serve as helpers for the same basic biochemical process: activating certain proteins by adding a chemical tag to them. But where they do this work differs significantly. K1 is preferentially retained in the liver, where it activates the proteins responsible for blood clotting. This is the role most people associate with vitamin K, and it’s why newborns receive a vitamin K shot at birth and why people on blood thinners are told to keep their vitamin K intake consistent.
K2 takes a different path. Rather than staying in the liver, it gets redistributed through the bloodstream to tissues like bone and blood vessel walls. There, it activates proteins that manage where calcium goes in your body. One of these proteins directs calcium into bones and teeth, strengthening them. Another prevents calcium from accumulating in your arteries and soft tissues. Your body can also convert some K1 into a short-chain form of K2 (called MK-4) in these tissues, which highlights how important K2’s role is outside the liver.
K2 Itself Comes in Multiple Forms
Vitamin K2 isn’t a single compound either. It’s a family of molecules designated MK-2 through MK-13, where the number refers to the length of the side chain. In practice, two forms get the most attention: MK-4 and MK-7.
MK-4 is found in animal products like egg yolks, butter, and organ meats. It has a short half-life in the body, meaning it’s used up relatively quickly. Supplemental doses of MK-4 tend to be much higher (often 45 mg) to compensate for this rapid turnover. MK-7, on the other hand, comes primarily from bacterial fermentation. Natto, a traditional Japanese dish made from fermented soybeans, is by far the richest dietary source. MK-7 stays in your bloodstream much longer than MK-4, so it can be taken in smaller doses and still maintain steady levels throughout the day. Most K2 supplements use MK-7 for this reason.
Where You Get Each Form
K1 is easy to get if you eat vegetables. A single cup of cooked kale or spinach delivers several times the daily recommended intake. K2 is harder to come by. The richest sources are natto (which many Western palates find challenging), certain aged cheeses, egg yolks, liver, and other organ meats. Some fermented dairy products contain moderate amounts. Because K2 is less abundant in typical Western diets, some people supplement it specifically, even if they’re getting plenty of K1 from vegetables.
Both forms are fat-soluble, so eating them with some dietary fat improves absorption. A salad drizzled with olive oil, for instance, helps your body absorb the K1 in the greens more efficiently than eating them plain.
Official Intake Recommendations
Current guidelines from the National Institutes of Health set adequate intake levels for vitamin K as a whole, not for K1 and K2 separately. For adults 19 and older, the recommendation is 120 mcg per day for men and 90 mcg for women. These values are based primarily on K1 intake, since food composition databases track K1 much more thoroughly than K2. No separate K2 target has been established, partly because data on how much K2 people consume (and how much their gut bacteria produce) is still limited.
This is worth keeping in mind if you’re evaluating your own diet. You could easily meet the official vitamin K target with a serving of leafy greens, but that wouldn’t tell you much about your K2 status specifically.
Why the Distinction Matters
If you searched this question because you saw K2 on a supplement label, here’s the practical takeaway: K2 is a specific subset of vitamin K with functions that go beyond blood clotting. Its role in directing calcium away from arteries and into bones is the main reason it appears in bone health and cardiovascular supplements, often paired with vitamin D. Getting enough K1 from vegetables supports normal clotting, but it doesn’t necessarily mean your bones and blood vessels are getting the K2 they need, because K1 is largely used up by the liver before it reaches those tissues.
So while K2 is technically a type of vitamin K, treating them as interchangeable misses an important distinction in how your body uses each one.