Vitamin K is a term used for a group of related fat-soluble substances known as naphthoquinones. This group includes vitamins K1, K2, and K3. Phylloquinone, the form of vitamin K found in plants is named Vitamin K1, while menaquinone mainly produced by the intestinal bacteria is termed K2, according to the book “Staying Healthy with Nutrition” by Elson Haas, M. D. There is also a synthetic version of vitamin K, menadione, or vitamin K3. Good plant sources of vitamin K are dark leafy greens, alfalfa, and kelp. Some vitamin K2 is found in animal sources, such as liver, egg yolks, and fish liver oils, as well as in fermented food products like cheese and natto (a fermented soybean food). Vitamin K is well known for its role in blood coagulation, but its benefits extend beyond that to include a role in bone metabolism and protection against osteoporosis, prevention of heart disease and kidney stones.
Vitamin K plays an essential role in the formation of strong bones, including teeth. Low blood levels of vitamin K are associated with reduced bone density. According to the October 2001 review article published in the “Nutrition”, vitamin K can not only increase bone mineral density in people with osteoporosis, but also reduce fracture rates. Vitamin K is necessary for the activation of osteocalcin. Osteocalcin is a protein that acts as a structural foundation helping hold calcium in place in the bones, according to the book “Encyclopedia of Natural Medicine”. According to the book “Prescription for Nutritional Healing”, vitamin K also helps the body to retain calcium by reducing its loss in the urine, thus making more calcium available for bone-building process. An October 2007 issue of the “Nutrition in Clinical Practice” states that long-term use of coumarin-based anticoagulants can negatively effect bone density and increase fracture risk, by interfering with vitamin K function.
Vitamin K deficiency has been associated with increased calcification of the main arteries and with insulin resistance. A systematic review of the literature, the results of which were published in the October 2010 issue of the “Maturitas”, found two studies examining the effects of vitamin K2 intake on the incidence of CHD (Coronary Heart Disease). Both found significant associations where higher vitamin K2 intake was associated with fewer CHD incidents. The association between vitamin K1 and CHD wasn’t as strong in other studies examined. A September 2010 review article published in the “Acta Physiologica Hungarica” found that a certain vitamin K-dependent protein (matrix-Gla protein or MGP) was a strong inhibitor of the arterial calcification. Again, Vitamin K2 was found to be more important for vascular system, than vitamin K1. An optimal vitamin K2 intake is therefore essential to significantly reduce the risk and rate of vascular calcification. An article published in the 2001 “Journal of Cardiology” notes that the present RDA values for vitamin K are too low to ensure full activation of MGP. More research is needed to determine optimal levels of vitamin K intake for the prevention of CHD.
Vitamin K also has an important role in the inhibition of kidney stone formation. Osteopontin is another protein that needs to be activated by vitamin K in order to be functional. The findings of a study published in the August 2001 issue of the “Chinese Medical Journal” indicate that osteopontin may be an important protein in the prevention of kidney stone formation. Another study showed that the cells of the kidney produce larger amounts of osteopontin to prevent the development of kidney stones.
Only the synthetic form of Vitamin K (K3) is associated with any degree of toxicity. Supplemental vitamin K overdose can cause hemolytic anemia, in which the red blood cells die much faster than the body is able to replenish them. Talk to your physician and/ or pharmacist before taking supplemental vitamin K, or consuming vitamin K rich foods, especially if you are taking anticoagulants/blood thinners.