Overview
Vitamin K is wildly more important than the medical narrative of "K stands for clot" suggests, and doctors have largely been taught the opposite of what the physiology actually does. Beyond producing the clotting factors, vitamin K carboxylates the proteins that bind calcium into bones and keep it out of arteries, kidneys, and other soft tissues. It works alongside coenzyme Q10 to maintain mitochondrial oxidative energy production, supports brain and blood vessel repair, and at higher doses inhibits monoamine oxidase B and increases steroid production. Big doses have been used to reverse osteoporosis rather than just slow its progress, bring extreme hypertension into the normal range within a week or two, and restore aging animals to youthful testosterone levels. The Japanese have used doses 500 times the standard dietary requirement with no toxicity. Two of the most important anti-clotting proteins, protein C and protein S, cannot be made without it.
Key Points
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Vitamin K's primary role is regulating where calcium goes in the body. It carboxylates the proteins that lock calcium into bones, and it keeps calcium out of arteries, kidneys, and other soft tissues. Deficient people accumulate arterial calcium, become stiff, and develop a wide gap between systolic and diastolic blood pressure as the arteries lose elasticity. Big doses, around 30 to 50 mg per day, have closed a 100-point pulse pressure gap within a week or two and reversed established osteoporosis rather than just slowing it.
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It is misclassified as a clotting vitamin and the actual physiology is the opposite of what doctors are taught. Two essential anti-coagulation factors, protein C and protein S, cannot be made without vitamin K, so K's role is to balance the clotting system rather than push it toward clotting. Doctors trained on "K stands for clot" warn warfarin patients away from it, but the system regulates clot formation in both directions and depends on K for that balance.
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Vitamin K works with coenzyme Q10 to keep mitochondria producing energy oxidatively. It is structurally a quinone, and it acts as an extension or amplifier of CoQ10, helping feed electrons through the respiratory chain to oxygen and producing ATP and carbon dioxide rather than lactic acid. CoQ10 stabilises vitamin K and vitamin K stabilises CoQ10, and the system runs as a unit. This explains why supplementation often improves endurance, blood sugar handling, and general cellular performance well beyond anything related to clotting.
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Aspirin should always be paired with vitamin K when taken regularly. The famous bleeding risk of aspirin comes from interfering with the clotting proteins the liver produces under vitamin K's direction. The standard ratio is roughly 1 mg of vitamin K per 325 mg aspirin tablet. People taking antibiotics with aspirin are particularly at risk because the antibiotics wipe out the intestinal bacteria that produce additional vitamin K.
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Vitamin K is structurally analogous to several known anti-cancer compounds. Emodin from cascara and aloe, lapachol from the South American Pau d'Arco tree, and the tetracycline antibiotics are all in this same quinone family. They protect mitochondria from being poisoned, support oxidative metabolism, and have a long history of use against cancer. The Russians published positive results on vitamin K in cancer and brain disease in the 1950s, but the work was not followed up.
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Higher doses are anti-estrogenic and support steroid production. Studies show very old rats given the human equivalent of about 100 mg of vitamin K return to the testosterone levels of (the equivalent of) 20-year-old rats. Vitamin K also acts as a monoamine oxidase B inhibitor, comparable to the anti-aging drug selegiline, which gives it a generally pro-cognitive and mood-supporting effect in older men.
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The richest food sources are kale, liver and aged cheese. A serving of well-cooked kale every other day provides enough K for ordinary needs. Liver eaten once or twice a month is a very rich source and supplies the full mixture of K1 and K2 forms. Intestinal bacteria also produce K, but this is unreliable because diet, antibiotics, and stress easily disrupt the producing flora. Counting on gut production alone is not safe.
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MK4 is the active cofactor; MK7 has longer blood half-life but is not directly usable. Vitamin K2 MK4 (menatetrenone) is the form the body uses as a cofactor for gamma-glutamyl carboxylase, which carboxylates osteocalcin and many other proteins including peptide hormones like insulin. MK7 has a longer lipophilic side chain and stays in blood longer, but it has to be cleaved back to MK4 to do its work. K1 (phylloquinone, from green leafy vegetables) acts as a quinone but is mainly hemostatic; only MK4 carboxylates. MK3 (menadione) is a cheap synthetic form that Georgi does not recommend.
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Anti-estrogenic, stronger than tamoxifen in yeast assays. Georgi's research group in Bulgaria tested vitamin K1, MK4, MK7, and MK3 in yeast estrogen and androgen assays. All forms were anti-estrogenic, with MK4 the strongest, MK7 weaker. Vitamin K is also a mild aromatase inhibitor, and converts estradiol back into the weaker estrone. The concentrations used in the assay translate to roughly 10 mg twice daily in humans.
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MK4 is in clinical trials for liver cancer and various blood cancers. The mechanism is the same quinone effect: tumours represent extreme metabolic derangement where electrons are stuck rather than flowing to oxygen, and vitamin K removes those stuck electrons, preventing the cell from continuing to build tumour mass. There is also the strongest known inverse correlation between any nutrient and diabetes for vitamin K.
Notable Quotes
"It's not the simple clotting vitamin that it's medically known as. It's a brain repair, blood vessel repair, bone repair, and can prevent excess clotting."
[Ray Peat — KMUD: Questions and Answers, January 2014]
"The blood clot system is incredibly complicated, and two of the essential factors are called protein C and protein S, and they happen to prevent abnormal coagulation, and you can't make them without vitamin K."
[Ray Peat — KMUD: Questions and Answers, January 2014]
"I think a serving of well-cooked kale every other day will give enough vitamin K (to prevent blood thinning effects of aspirin)."
[Ray Peat — KMUD: Hair Loss, Inflammation, Osteoporosis]
"The Japanese have treated osteoporosis and hardening of the arteries with doses of vitamin K that were 500 times the normal dietary requirement. It's safe even at those high levels."
[Ray Peat — KMUD: Hair Loss, Inflammation, Osteoporosis]
"Vitamin K, it happens to be a pretty expensive vitamin, but it is right at the center of the regulation of calcium. It protects your arteries from calcification, and it allows the bone to use carbon dioxide. It carboxylates the proteins that bind calcium into the bone."
[Ray Peat — KMUD: Hair Loss, Inflammation, Osteoporosis]
"It's working as an extension or amplifier of coenzyme Q10. It associates with that and helps feed energy into the mitochondria."
[Ray Peat — Generative Energy #43: Body Temperature, Inflammation, and Aging]
"It triggers the synthesis of testosterone in the gonads of older males that exceed four times the synthesis rate of testosterone in younger males."
[Georgi Dinkov — Get Lean E-Clean Podcast]
Important Things To Consider
Pair vitamin K with chronic aspirin to prevent bleeding. Roughly 1 mg of vitamin K per 325 mg aspirin tablet covers the risk for ordinary use. People taking 6 or 7 grams of aspirin per day for chronic conditions need correspondingly more. The bleeding tendency comes from aspirin disabling the clotting proteins the liver makes under vitamin K's direction, so the K replaces what aspirin blocks.
Antibiotic use can produce a hidden vitamin K deficiency. The intestinal bacteria that make vitamin K are wiped out by antibiotics, so anyone combining antibiotics with aspirin is at higher risk of bleeding even on what would otherwise be a safe aspirin dose. Eating cooked greens, liver, and aged cheese during and after antibiotics restores intake from the diet directly.
Synthetic vitamin K is not interchangeable with natural K1 and K2. Ray prefers the natural forms over synthetic K, both because of cleaner action and because the natural mixture covers the spectrum of K1, MK-4, and MK-7 forms.
Big doses can drop blood pressure quickly, so monitor if already on antihypertensives. Multiple cases describe people lowering systolic by 80 to 100 points within a week or two on doses of 30 to 50 mg per day. One person taking a hypertension drug had to stop the drug after starting K because his blood pressure went too low. People with normal pressure should be cautious with very large doses.
Vitamin D and vitamin K need each other and need adequate calcium and magnesium. Taking vitamin D without sufficient calcium can drive parathyroid hormone effects that mobilise calcium out of bone and into soft tissue. K directs calcium into bone and out of arteries, but only when there is enough calcium and magnesium intake to work with. The system fails if any of the inputs is missing.
Take vitamin K and vitamin E at separate times of day. They form a charge-transfer complex that becomes light-sensitive in circulation, so taking them together followed by bright sunlight can produce unwanted oxidative effects. Spacing them by a few hours avoids this.
The standard medical position on K and warfarin should be questioned, not accepted at face value. Ray has not heard of vitamin K being a problem alongside blood thinners like Pradaxa, and he has framed the warfarin-K antagonism as the reason for medical fear of K rather than evidence that K itself causes pathological clotting. People on these drugs should still have their clotting parameters checked periodically.
Tooth decay is partly a calcium-regulation problem that K helps address. Vitamin D and vitamin K together keep calcium in dentine and enamel rather than letting stress mobilise it out, so adequate K intake is part of supporting dental as well as skeletal calcium retention. The "stress" type of cavity that starts as a white area on the tooth is essentially a localised calcium-mobilisation event.
Vitamin K2 is an approved osteoporosis drug in Japan, Indonesia, Singapore, Vietnam, and South Korea. The drug is called Glakay, dosed at 15 to 45 mg daily.
Avoid the MK3 (menadione) form. It is a cheap synthetic version of vitamin K used in some countries. Georgi explicitly does not recommend it, even though it tested as anti-estrogenic in his group's yeast assays.
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