Vitamin K is a fat-soluble vitamin that plays an important role in regulating blood clotting. In the past couple of decades, it has become evident that vitamin K plays a larger role in human health that is beyond its well-established function in blood clotting. Studies have demonstrated that vitamin K can increase bone mineral density and also reduce fracture rates (1).
Vitamin K is a broad term for a group of chemically related fat-soluble vitamins known as naphthoquinones. This group includes vitamins K1, K2 and K3. Vitamin K1 (phytonadione) and vitamin K2 are the primary sources that humans obtain through foods.
Vitamin K1 can be found in green, leafy vegetables (such as kale, spinach, turnip greens, collards, Swiss chard and mustard greens); K2 is found in fermented products and fish, liver and meat.
Vitamin K2 is also made by the bacteria in the lower intestinal tract (2).
Data suggests that only about one in four Americans meets the goal for vitamin K intake from food. Vitamin K deficiency increases the risk of excessive bleeding, and an injection is recommended to protect all newborns from life-threatening bleeding within the skull (3).
The Research
Benefits
Vitamin K and blood clotting go hand-in-hand. Vitamin K was originally identified for its role in the process of blood clot formation (“K” is derived from the German word “koagulation”) and helps make 13 proteins needed for blood clotting (4). Without vitamin K, the body cannot produce prothrombin, a clotting factor that is necessary for blood clotting.
Vitamin K may play a role in preventing heart disease. Vascular calcifications are mineral deposits on the walls of arteries and veins. Calcification of the coronary arteries is highly prevalent in patients with coronary heart disease (CHD) and is associated with major adverse cardiovascular events (5).
Vitamin K activates a protein that helps slow the progression of coronary artery calcification (6).
Vitamin K helps build bone and prevent fractures. Low levels of circulating vitamin K have been linked with low bone density, and supplementation with vitamin K shows improvements in biochemical measures of bone health.
Osteoporosis means “porous bone” and is a bone disease that occurs when the body loses too much bone, makes too little bone, or both. As bones become less dense, they weaken and are more likely to break (7).
According to the results of a study published in the Journal of Bone and Mineral Research, vitamin K2 treatment was found to be effective in preventing fractures in those diagnosed with osteoporosis. A total of 241 volunteers were enrolled in a 24-month randomized open label study, and received 45mg of the supplement daily for 2 years.
Supplementation reduced both the fracture rate as well as prevented the loss of bone mineral density in the spinal region relative to placebo. While there was some increase in bone mineral density after the testing period, the effect was not significant (8).
In another study, researchers investigating whether low-dose vitamin K2 supplements could beneficially affect bone health, were met with promising results. Healthy postmenopausal women received vitamin K2 capsules or placebo for 3 years.
Supplementation significantly decreased the age-related decline in bone mineral density and bone mineral content at the lumbar spine and femoral neck, but not at the total hip. Bone strength was also favorably affected and significantly decreased the loss in vertebral height of the lower thoracic region at the mid-site of the vertebrae (9).
Vitamin K may help improve cognitive function. In a recent study of 320 men and women aged 70 to 85 years without cognitive impairment, those with the highest blood levels of vitamin K1 had the highest verbal episodic memory performance (10).
In another study, increased dietary vitamin K intake was associated with fewer and less severe subjective memory complaints in older adults (11). Future studies are needed to help researchers better understand the vitamin’s role in memory and cognition in older adults.
Vitamin K may play a role in treating cancer. In recent years, several studies have shown that vitamin K2 has anticancer activity in a variety of cancer cells. In one study, researchers who set out to evaluate the anticancer potential of the vitamin against prostate cancer cells found promising results.
Treatment reduced cell migration and angiogenesis potential (an important factor in the progression of cancer) of prostate cancer cells. Researchers also noted an anti-inflammatory effect as several inflammatory genes were downregulated in prostate cancer cells following treatment (12).
The results of an in vitro study published in the International Journal of Molecular Medicine, suggested that vitamin K2 induced human colon cancer cell death by several different mechanisms and suppressed the growth of colon tumors implanted into mice (13).
Vitamin K may help treat diabetes. In a group of healthy volunteers between 26 and 81 years old, higher dietary vitamin K1 intake was associated with greater insulin sensitivity and lower post-meal glucose levels (14).
Another study found that intake of vitamin K1 is associated with a reduced risk of type 2 diabetes in older adults at high risk for cardiovascular disease; the risk of developing type 2 diabetes was reduced by 17 percent per 100 micrograms of K1 intake per day (15).
Side effects
Toxicity is rare and unlikely to result from eating foods containing vitamin K. Though allergic reactions have occurred with vitamin K injections, no incidence of actual toxicity has been reported in people taking vitamin K supplements.
It is important to note, however, that long-term, high-dose studies on vitamin K safety are lacking.
People who take anticoagulants such as warfarin (Coumadin) must be careful when taking supplements or foods containing this vitamin as it can affect how these drugs work. A medical professional should be notified prior to any vitamin K usage if currently taking blood thinners.
Recommended dosage
Most people get enough vitamin K from their diets when they eat such foods as green leafy vegetables, broccoli, cabbage, meat, liver, soybeans and cheese.
According to the National Institutes of Health, the amount of vitamin K needed depends on age and sex; adult men 19 years and older need 120 mcg daily; adult women 19 years and older need 90 mcg daily (16).
Recap
Vitamin K is a fat-soluble vitamin that plays an important role in regulating blood clotting. Studies also show its potential in helping build bone and preventing fractures. There are also reports of its ability to help prevent heart disease, treat certain types of cancer and improve cognitive function. While further in-depth studies are needed, early results are promising.
Most people get enough vitamin K by eating a healthy, balanced diet that includes green leafy vegetables, fish, liver and meat.