Role of vitamin k

I have heard reports discussing recent studies identifying a role for vitamin K in processes other than clotting.  How is vitamin K involved in clotting and what other processes may it be involved in?

Vitamin K is a fat-soluble vitamin that exists in three forms, two of which are naturally occurring.  It is stored in the body’s fat tissue and liver and is best known for its role in helping blood clot.  In fact, the “K” comes from the German word “koagulation”.  Vitamin K has key functions in the blood coagulation pathway as it makes one third of the proteins involved in the process.  However, recent data seems to point to a role for vitamin K in bone metabolism and possibly even cancer prevention.

What are the links between vitamin K and bone density?

Proper use of calcium in bones requires vitamin K- higher levels are correlated with greater bone density, while lower levels are linked with osteoporosis.  Furthermore, one study found that osteoporosis patients who suffer fractures have vitamin K levels that are much lower than those of their age-matched controls.  In clinical studies, both men and women whose vitamin K intakes were among the lowest of those studied had a higher risk of hip fracture than those whose intakes were among the highest.  Furthermore, long-term observation of post-menopausal women showed that in a given time period, those who took vitamin K supplements not only suffered fewer fractures, but also had lower rates of cancer occurrence, specifically non-Hodkins lymphoma.  The later needs further research.

How will I know if I am not getting enough vitamin K?

Vitamin K deficiency is rare because in addition to being abundant in leafy green vegetables, vitamin K is made by the bacteria that are found in the intestines.  However, the body stores very little of it so it is important to have regular dietary intake of vitamin K to avoid deficiency, which results in clotting problems.  Symptoms include bruising, nosebleeds, bleeding gums, blood in the urine or stool, tar-like stools, and/or extremely heavy menstrual bleeding.

Certain conditions can prevent the absorption of vitamin K.  Therefore, individuals with gallbladder or biliary disease, cystic fibrosis, celiac disease, Crohn’s disease, liver disease, serious burns, or those using blood-thinners or on hemodialysis, should be particularly aware of these symptoms.

Are there any risks to taking vitamin K supplements?

Individuals taking anticoagulants such as warfarin (Coumadin) must keep their vitamin K intake stable and thus should not begin a vitamin K supplement without an explicit directive from their physician.  Other medications that may be affected by increasing your circulating vitamin K levels are antibiotics, dilantin, orlistat, olestra and bile acid sequestrants.  Aside from its effect on these medications, there is no known toxicity associated with high doses of vitamin K intake and supplements are well-tolerated.  As with any nutritional regimen, you should consult with your health care provider before starting vitamin K supplements.

References:

Cheung, A. M., (2008).  Vitamin K Supplementation in Postmenopausal Women With Osteopenia (ECKO Trial):  a Randomized Controlled Trial.  PLoS Medicine.  5 (10), e196.

Nieves, J. W., (2005).  Osteoporosis:  the Role of Micronutrients.  American Journal of Clinical Nutrition.  81 (5), 1232S-1239S.

http://lpi.oregonstate.edu/

http://www.hsph.harvard.edu/

http://www.umm.edu/

http://www.webmd.com/

http://www.womenshealth.gov/