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Vitamin K

Vitamin K is an essential vitamin found in plants or produced from intestinal bacteria. It plays an essential role in bone health and regulates blood clotting.

Our evidence-based analysis on vitamin k features 492 unique references to scientific papers.

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Summary of Vitamin K

Primary information, health benefits, side effects, usage, and other important details

Vitamin K is an essential vitamin. It is one of the four fat-soluble vitamins, along with vitamin A, vitamin D, and vitamin E. It was named vitamin K after the German word koagulation, because vitamin K’s role in blood coagulation was first discovered in Germany. Vitamin K can be found in dark green vegetables, matcha tea and natto (fermented soybeans). Vitamin K2 can also be found in animal products, since it is a result of bacterial fermentation.

The Recommended Daily Intake (RDI) of vitamin K is sufficient to support healthy blood coagulation. Higher levels of vitamin K, however, provide benefits for cardiovascular and bone health. Unfortunately, it is difficult to obtain high levels of vitamin K from food alone. Most people don’t like natto enough to eat 50g a day, so supplementation of vitamin K is a popular option.

Optimal levels of vitamin K are associated with improved bone circumference and diameter. Vitamin K can also protect cardiovascular health. It reduces the calcification and stiffening of arteries, which reduces the risk of cardiovascular-related mortality. Vitamin K may have a role to play in cancer therapy and anti-aging treatments. It may also help with regulating insulin sensitivity and reducing skin reddening, but more research is needed to determine if vitamin K has an active role to play in these areas.

Vitamin K’s main mechanism is through the vitamin K cycle, which is a cyclical metabolic pathway that uses vitamin K to target specific proteins. When a protein expresses glutamate, it is targetted by vitamin K, which causes it to collect more calcium ions. Calcium ions are removed from the blood stream, which prevents buildup in the arteries.

Vitamin K is often supplemented alongside vitamin D, since vitamin D also supports bone health. In fact, taking both together will improve the effects of each, since they are known to work synergistically. Excessive vitamin D can lead to arterial calcification, but vitamin K reduces this buildup.

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How to Take

Recommended dosage, active amounts, other details

Vitamin K comes in a variety of different forms, known as vitamers. Forms of vitamin K are either phylloquinones (vitamin K1) or menaquinones (vitamin K2). There are different vitamers within the vitamin K2 class, abbreviated as MK-x.

The minimum effective dose for phylloquinone (vitamin K1) is 50mcg, which is enough to satisfy the Recommended Daily Intake (RDI) for vitamin K. The maximum dose for vitamin K1 is 1,000mcg.

The minimum effective dose for short chain menaquinones (MK-4) is 1,500mcg. Doses of up to 45mg (45,000mcg) have been safely used in a superloading dosing protocol.

The minimum effective dose for longer chain menaquinones (MK-7, MK-8, and MK-9) is between 90-360mcg. Further research is needed to determine the maximum effective dose for MK-7.

A topical application of vitamin K should contain at least 5% phylloquinone.

Vitamin K should be supplemented alongside fatty acids, even if the vitamin is coming from a plant-based source, so consider taking vitamin K at meal time. Microwaving plant-based sources of vitamin K will increase the absorption rate of the vitamin.

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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects Vitamin K has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-a Notable Moderate See all 15 studies
There appears to be a relative increase in bone mineral density associated with vitamin K supplementation, due to attenuating the rate of bone loss in older individuals. Although it is significant overall in meta-analyses, it is quite unreliable and similar in potency to vitamin D when it occurs (less than estrogen replacement therapy)
grade-b - High See all 3 studies
Although there may be a role for topical vitamin K in reducing the severity of bruising, currently the evidence is too unreliable to draw conclusions and is not looking promising. Menaquinones have not been tested yet
grade-b - Very High See all 3 studies
In studies that measure weight changes over time (usually as a secondary piece of data), there do not appear to be any significant alterations associated with vitamin K supplementation.
grade-c Notable Very High See 2 studies
The decrease in fracture risk seen with vitamin K supplementation in susceptible cohorts appears to be greater than seen with other supplements
grade-c Notable Very High See 2 studies
Although the studies have used superloading of vitamin K (40mg or more) and only in hepatic cancers, the reduction in mortality risk and prolongation of survival times appears to be quite notable
grade-c Notable Very High See 2 studies
Recurrence rates of hepatocellular carcinoma appears to be significantly less than placebo when using vitamin K in a superloading scheme (40mg or more daily)
grade-c Minor - See study
An improvement of insulin sensitivity has been noted with 30mg of MK-4 supplementation over 4 weeks in otherwise healthy individuals, with the influence of lower doses of vitamin K not ascertained
grade-c Minor Very High See 2 studies
It appears that for conditions with reddened skin (purpura or bags under the eyes) that vitamin K may have a role in removing the blood from the skin and reducing redness when 5% phylloquinone is applied to the skin. Mechanisms are not known, and study quality at the moment is lacklustre
grade-c - - See study
No significant alterations seen in adiponectin concentrations in serum with 4 weeks supplementation of 30mg MK-4
grade-c - - See study
Despite an improvement in insulin sensitivity, the lone study failed to note any significant changes in blood glucose concentrations in a fasted state
grade-c - Very High See 2 studies
No significant influence on C-reactive protein (an inflammatory biomarker) seen with vitamin K supplementation
grade-c - - See study
No significant interactions with estrogen noted with vitamin K supplementation
grade-c - - See study
Studies that happen to measure dietary intake fail to note any influence of supplemental Vitamin K
grade-c - - See study
Vitamin K does not appear capable of influencing HDL cholesterol
grade-c - Very High See 2 studies
No significant effect of vitamin K on circulating levels of IL-6, an inflammatory marker
grade-c - - See study
LDL-C appears to be unaffected by supplemental vitamin K
grade-c - - See study
No significant alterations noted with vitamin K supplementation on osteoprotegerin
grade-c - - See study
No significant interactions with total cholesterol concentrations in persons given vitamin K supplementation
grade-c - - See study
No significant influence on circulating triglycerides seen with MK-4 supplementation
grade-d Minor Moderate See 2 studies
A relative deficiency of vitamin K seems to be associated with higher post-meal insulin spikes (over 120 minutes), and this abnormal elevation is normalized upon supplementation of vitamin K

Studies Excluded from Consideration

  • Confounded with an assortment of other vitamins[1]

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Frequently Asked Questions and Articles on Vitamin K

Should you supplement with vitamin K?
Research is still scarce, but current evidence suggests that, through their effect on calcium regulation, some forms of vitamin K can help prevent osteoporosis and cardiovascular diseases.
5 supplements (and foods) for a stronger heart
Cardiovascular diseases (CVDs) are the #1 cause of death globally. But a mix of the right foods and complementary supplements can help decrease your risk factors.

Things to Note

Primary Function:

Also Known As

Phylloquinone, Menaquinone, MK-4, MK-7, Menatetrenone, Phytonadione

Do Not Confuse With

Pyrroloquinoline quinone (sounds similar to phylloquinone, totally different molecule)

Goes Well With

  • Vitamin D (for bone and cardivascular health effects)

  • Sufficient levels of dietary Calcium and Magnesium (for supporting bone health)

  • Vitamin C (potentially the anticancer properties)

  • Sesamin (increases phylloquinone and MK-4 retention in the body)

Caution Notice

Vitamin K is known to interact significantly with warfarin usage, and tends to suppress the effects of warfarin. Your medical professional should be notified of any vitamin K usage if currently using warfarin.

  • Vitamin K is fat soluble (and the longer chain a menaquinone gets, the more fat soluble it becomes) and needs to be ingested either with a fat-containing meal or with a capsule containing fatty acids

  • Menadione (Vitamin K3) tends to actually have a toxicity associated with it rather than the pretty safe menaquinones and phylloquinone

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