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 cyclic metabolic pathway that uses vitamin K to target specific proteins. When a protein expresses glutamate, it is targeted by vitamin K, which causes it to collect more calcium ions. Calcium ions are removed from the bloodstream, 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.
The Human Effect Matrix from examine.com summarises human studies to tell you what effects Vitamin K has on your body, how much evidence there is, and how strong these effects are.
Bone mineral density: 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).
Bone fracture risk: The decrease in fracture risk seen with vitamin K supplementation in susceptible cohorts appears to be greater than seen with other supplements
Cancer mortality: 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 rates of hepatocellular carcinoma: Recurrence rates of hepatocellular carcinoma appears to be significantly less than placebo when using vitamin K in a superloading scheme (40mg or more daily)
Vitamin K comes in a variety of different forms, known as vitamers. Forms of vitamin K are either phylloquinones (vitamin K