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 (a type of fermented soybeans). Vitamin K can also be found in various animal products.
The Recommended Daily Intake (RDI) of vitamin K is sufficient to support healthy blood coagulation. Higher levels of vitamin K, however, may provide additional benefits. Unfortunately, it can be 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.
Vitamin K has at times been found to improve markers of bone health. Despite this, supplementation has inconsistent effects on bone fracture risk.
Vitamin K has been suggested to protect cardiovascular health by reducing the calcification and stiffening of arteries. However, a number of clinical trials have found no apparent effect of vitamin K supplementation on arterial calcification. Most of these trials were on people with extensive arterial calcification already present, meaning additional research is needed to determine if vitamin K can prevent tissue calcification before it has started.
Vitamin K may have a role to play in cancer therapy. It may also help with regulating insulin sensitivity and (in topical form) may help reduce skin reddening, but more research is needed before strong conclusions can be drawn.
Vitamin K’s main mechanism is through the vitamin K cycle, which is a cyclical metabolic pathway that uses vitamin K to modify various proteins. Specifically, vitamin K is used to attach a carbon dioxide molecule onto a glutamate contained in these proteins, allowing the protein to bind calcium ions. These proteins can then utilize calcium ions for various biological processes.
Vitamin K is often supplemented alongside vitamin D, since vitamin D also supports bone health. In fact, taking both together may improve the effects of each, since they are believed to work synergistically. Excessive vitamin D can lead to arterial calcification and in animal models vitamin K reduces this buildup.