There is no official recommended daily allowance specifically for vitamin K2. Health authorities set an “Adequate Intake” for total vitamin K (K1 and K2 combined) of 120 mcg per day for adult men and 90 mcg per day for adult women, but nearly all of that guidance is based on K1, the form found in leafy greens. Most people searching for a K2 dosage are looking at supplements, and the range used in clinical research falls between 100 and 360 mcg per day of the MK-7 form, depending on the health goal.
Why There’s No Official K2 Number
Vitamin K comes in two main forms. K1 (found in spinach, kale, and broccoli) handles blood clotting. K2 (found in fermented foods, cheese, and egg yolks) plays a bigger role in directing calcium into bones and away from arteries. Despite their different jobs, nutrition guidelines lump them together. The NIH’s Adequate Intake of 90 to 120 mcg for adults is based almost entirely on K1 research, so it doesn’t tell you much about how much K2 you specifically need.
No upper limit has been set for any form of vitamin K. The Food and Nutrition Board has stated that no adverse effects from vitamin K consumption, whether from food or supplements, have been reported in humans or animals. That doesn’t mean more is always better, but it does mean toxicity isn’t a realistic concern at typical supplement doses.
Dosages Used in Clinical Research
The MK-7 form of K2 is the most widely studied in supplement form because it stays active in the body for days, compared to hours for other forms. In clinical trials focused on arterial and bone health, daily MK-7 doses have ranged from 90 mcg up to 400 mcg. The most common doses across 14 randomized controlled trials reviewed in a 2023 meta-analysis were 180, 200, and 360 mcg per day. That review, published in Frontiers in Nutrition, found that K2 supplementation significantly slowed the progression of coronary artery calcification.
A separate form called MK-4 is used at dramatically higher doses, typically 15 to 45 mg per day (that’s 15,000 to 45,000 mcg). These pharmaceutical-level doses have been studied for bone health, particularly in Japan where MK-4 is used as a prescription treatment for osteoporosis. MK-4 clears the bloodstream within hours, which is why the doses are so much larger than MK-7.
For most people buying an over-the-counter supplement, MK-7 in the range of 100 to 200 mcg daily is the most practical starting point. If you’re supplementing specifically for cardiovascular or bone support, studies suggest 180 to 360 mcg of MK-7 per day is the range where benefits have been measured.
MK-7 vs. MK-4: Picking a Form
MK-7 and MK-4 are both vitamin K2, but they behave differently in your body. MK-7 has a long half-life, meaning a single daily dose keeps blood levels elevated for two to three days. This makes it effective at lower doses and convenient to take once a day. MK-4 peaks and drops quickly, so studies use much higher amounts split across multiple doses.
Most supplements on the market contain MK-7, often in 100 or 200 mcg capsules. If you see a K2 supplement with a dose in the milligram range (like 5 mg or 45 mg), it’s almost certainly MK-4. Both forms activate the same proteins that manage calcium in your body, but MK-7 is the more practical choice for everyday supplementation.
Food Sources of K2
Natto, a Japanese dish made from fermented soybeans, is the richest dietary source by a wide margin. A 100-gram serving contains 800 to 1,100 mcg of MK-7. That single serving exceeds what most supplement capsules provide. Other fermented foods like fermented soy pastes contain smaller but meaningful amounts, ranging from 2 to 86 mcg per 100 grams depending on the product.
Animal foods provide K2 primarily as MK-4. Chicken thigh with skin contains about 53 mcg per 100 grams. Hard and blue cheeses offer 30 to 110 mcg per 100 grams, mostly as longer-chain forms like MK-8 and MK-9. Egg yolks come in at roughly 15 mcg per 100 grams, so you’d need several eggs to reach a meaningful dose. Dairy products like yogurt and kefir contain very small amounts, under 5 mcg per 100 grams.
Unless you eat natto regularly, it’s difficult to get therapeutic amounts of K2 from food alone. Most Western diets provide well under 50 mcg of K2 per day, which is why supplementation has become popular.
Taking K2 With Vitamin D
Vitamin K2 and vitamin D are frequently paired in supplements because they work on overlapping pathways. Vitamin D increases the production of proteins that need vitamin K2 to become activated. Without enough K2, the calcium that vitamin D helps you absorb can end up deposited in arteries rather than bones. If you take vitamin D supplements, adding K2 helps ensure calcium goes where it should.
There’s no precise ratio established, but combination supplements typically pair 1,000 to 5,000 IU of vitamin D3 with 100 to 200 mcg of MK-7. This pairing reflects the dosage ranges studied individually for each nutrient.
K2 and Blood Thinners
If you take warfarin or a similar blood thinner that works by blocking vitamin K, any form of supplemental K2 can interfere with your medication. Warfarin works precisely by reducing vitamin K activity, so adding K2 directly counteracts it. Even the 25 mcg of vitamin K found in some multivitamins has been documented in case reports to shift clotting levels enough to cause problems. People on warfarin need consistent vitamin K intake day to day, and adding a new K2 supplement without medical guidance can destabilize their dosing.
Newer blood thinners that don’t work through the vitamin K pathway don’t carry this same interaction risk.
How to Absorb K2 Effectively
Vitamin K2 is fat-soluble, meaning your body absorbs it through the same pathway as dietary fat. Taking a K2 supplement on an empty stomach reduces how much you actually absorb. The simplest approach is to take it with a meal that contains some fat, even a modest amount like what you’d get from eggs, cheese, nuts, or olive oil on a salad. Many K2 supplements are sold in oil-based softgel capsules, which helps with absorption even between meals, though taking them with food is still more reliable.