Plants only give you vitamin K1, and it converts poorly to the K2 you need
K1 and K2 are different, and plant foods other than fermented ones contain little K2. But the body does convert K1 to a form of K2 in its own tissues, no health body sets a separate K2 requirement, and the richest K2 source of any food is a fermented soybean dish. Vegan K2 supplements exist, made by the same bacteria that put K2 into cheese.
K1 and K2 are not interchangeable. K1 works mainly on blood clotting. K2 helps direct calcium into bones and teeth and away from arteries. The body's conversion of K1 to K2 is limited, and the foods richest in K2 are mostly animal or fermented ones. A diet of plants can therefore meet the official vitamin K figure while still being low in the form that may matter most for long-term bone, dental and heart health.
The distinction is real, but it does not leave a vegan diet short of anything that cannot be supplied.
Vitamin K1 comes mainly from leafy greens. K2 is a family of compounds called menaquinones. Most of them are made by bacteria. That is why they turn up in fermented foods like cheese and natto, and in smaller amounts in eggs and meat. So K2 is not an animal nutrient in origin. Animals either eat it, or make one form, MK-4, from K1.
Humans make MK-4 too. The body converts dietary K1 into MK-4 inside its own tissues, and that conversion is thought to be the main source of the MK-4 found in human tissue, in omnivores as well as vegans. "Doesn't convert very well" understates a process that works routinely.
No dietary authority sets a separate requirement for K2. Official recommendations cover vitamin K as a whole, and those amounts are easy to reach from greens. Vitamin K deficiency in healthy adults is rare, and studies of vegans have not shown it to be a problem.
For anyone who wants K2 specifically, there are good options. Natto contains more K2 per serving than any meat or cheese. Some other fermented foods add smaller amounts. K2 supplements, usually the MK-7 form, are made by bacterial fermentation and are suitable for vegans.
The claims about what K2 does need care. The link to teeth and jaw development comes mainly from Weston Price's observations in the 1930s, not from controlled studies. Evidence that K2 helps bones and arteries is mostly observational, and trial results are mixed. It may matter. If it does, the answer is the same: a fermented food or a supplement, not an animal.
It is also worth comparing with the realistic alternative. Most people on a typical Western diet eat little K2 either, so this is not a gap that eating meat reliably closes.
- Vegans miss out on vitamin K2, and that damages teeth
Different wording, same argument. The response above answers all of them.