Vitamin K

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.

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.

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects vitamin k has on your body, and how strong these effects are.

Grade	Level of Evidence [show legend]
	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.	Notes
	Bone Mineral Density	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)
	Bruising	-	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
	Weight	-	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.
	Bone Fracture Risk	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
	Cancer Mortality	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
	Recurrence of Hepatocellular Carcinoma	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)
	Insulin Sensitivity	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
	Reddening of the Skin	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
	Adiponectin	-	- See study	No significant alterations seen in adiponectin concentrations in serum with 4 weeks supplementation of 30mg MK-4
	Blood Glucose	-	- 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
	C-Reactive Protein	-	Very High See 2 studies	No significant influence on C-reactive protein (an inflammatory biomarker) seen with vitamin K supplementation
	Estrogen	-	- See study	No significant interactions with estrogen noted with vitamin K supplementation
	Food Intake	-	- See study	Studies that happen to measure dietary intake fail to note any influence of supplemental Vitamin K
	HDL-C	-	- See study	Vitamin K does not appear capable of influencing HDL cholesterol
	Interleukin 6	-	Very High See 2 studies	No significant effect of vitamin K on circulating levels of IL-6, an inflammatory marker
	LDL-C	-	- See study	LDL-C appears to be unaffected by supplemental vitamin K
	Osteoprotegerin	-	- See study	No significant alterations noted with vitamin K supplementation on osteoprotegerin
	Total Cholesterol	-	- See study	No significant interactions with total cholesterol concentrations in persons given vitamin K supplementation
	Triglycerides	-	- See study	No significant influence on circulating triglycerides seen with MK-4 supplementation
	Insulin	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]

• Vitamin K for vascular health
• Can vitamin K reduce body fat accumulation in postmenopausal women?

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