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The calcium director. K2 tells calcium where to go — into bones and teeth, not arteries and soft tissues.
Vitamin K2 activates proteins that direct calcium into bones and teeth while keeping it out of arteries and soft tissues. Without adequate K2, calcium can deposit in the wrong places — contributing to arterial calcification while bones remain weak.
This is especially relevant during the iodine protocol because improving thyroid function can increase calcium metabolism. K2 ensures that calcium goes where it's needed.
The two key proteins K2 activates are osteocalcin (which binds calcium into bone) and matrix GLA protein (which prevents calcium from depositing in arteries and soft tissue). Without K2, these proteins remain inactive — calcium floats around with nowhere productive to go.
Many people assume vitamin K is just one thing. In reality, K1 (phylloquinone) and K2 (menaquinone) serve very different roles. K1 is abundant in leafy greens and primarily supports blood clotting. K2 is the calcium director — a completely separate function.
The body can convert a small amount of K1 to K2, but the conversion rate is poor. Getting enough K2 from food or supplements directly is far more reliable. Most people eating a modern diet are getting plenty of K1 from salads and vegetables but very little K2.
This distinction matters because someone could eat a diet rich in leafy greens, have excellent K1 status, and still be profoundly deficient in K2 — leading to calcium landing in arteries instead of bones.
Within K2, there are two main forms worth knowing about. MK-4 is found in animal foods like egg yolks, butter from grass-fed cows, and organ meats. It is fast-acting but short-lived in the body — it needs to be consumed multiple times a day for sustained benefit.
MK-7 is produced by bacterial fermentation and found most notably in natto (a Japanese fermented soybean dish). MK-7 has a much longer half-life in the body, staying active for days rather than hours. This makes it the more practical supplemental form for most people.
Some in our community use both: MK-4 from dietary sources like pastured eggs and grass-fed butter, supplemented with an MK-7 capsule for sustained coverage.
Egg yolks, grass-fed butter, ghee, liver, and other organ meats. Short-acting — best consumed with meals throughout the day.
Natto is the richest source by far. Some aged cheeses and fermented vegetables provide small amounts. Most common supplemental form.
MK-7 at 100-200mcg daily covers most needs. Some formulas combine MK-4 and MK-7 for comprehensive support.
Vitamin D3 and K2 are inseparable partners. D3 increases calcium absorption from food — which is beneficial — but without K2 to direct that calcium, it can end up in arteries, kidneys, and joints. Supplementing D3 without K2 is like inviting guests to a party without telling them which room to go to.
This synergy is particularly important for those on the iodine protocol. As thyroid function improves, the body's calcium metabolism changes. Having both D3 and K2 on board ensures this transition goes smoothly, with calcium building bones rather than causing problems elsewhere.
If supplementing vitamin D3, always include K2. Vitamin D increases calcium absorption from food, and K2 ensures that absorbed calcium is directed to bones rather than arteries. A common pairing is 5,000 IU D3 with 100-200mcg K2 (MK-7).
The richest dietary sources of K2 are traditional foods that have largely disappeared from modern diets. Natto leads the list by a wide margin, but it is an acquired taste. Grass-fed butter, egg yolks from pastured hens, aged cheeses like Gouda and Brie, and organ meats like liver all provide meaningful amounts of K2.
For those who do not regularly eat these foods, supplementation fills the gap effectively. A daily MK-7 supplement of 100-200mcg is the most common approach in our community.
K2 is one of many supporting nutrients that work with iodine.