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Compared to vitamins D and C, vitamin K2 is the black sheep of the vitaminic family. In fact, the U.S. Department of Agriculture (USDA) didn’t even look into how much vitamin K2 was in our food until 2006. But it turns out this little-known nutrient may have major positive effects on your health, potentially lowering the risk of cardiovascular disease and prostate cancer.
- Vitamin K2 is a fat-soluble vitamin, like vitamin D; it’s stored in the body for future use.
- K2 plays an important role in blood clotting and bone metabolism.
- Vitamin K2 may also support cardiovascular health and protect against cancer.
- But the evidence isn’t definitive; more human studies are needed.
What is vitamin K2?
Vitamin K is a fat-soluble vitamin, meaning that it’s absorbed with fat in your diet and stored in the body (specifically, the liver and fat tissue) when it’s not being used. The other fat-soluble vitamins are A, D, and E. There are a group of K vitamins, of which the most important are K1 (phylloquinone) and K2 (menaquinones).
Vitamin K is crucial for blood coagulation and bone metabolism, among other functions. It was discovered by a Danish scientist in 1929 (in fact, the K originally stood for “koagulation”). Vitamin K1 and K2 are both used to make coagulation factors in the liver. Vitamin K2 also works as a kind of hall monitor for calcium — it’s used by tissues to ensure that calcium is deposited in the right places, like bones, and doesn’t build up in places it shouldn’t be, like the blood vessels and kidneys (Halder, 2019). The blood vessels produce a protein called MGP (or matrix GLA protein), which prevents calcium from building up on their walls and possibly causing blockages; vitamin K2 is essential to the formation of MGP.
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Vitamin K1 is mainly found in leafy green vegetables. Vitamin K2 is largely found in animal sources (like meat and egg yolks) and fermented foods; it’s also produced by gut bacteria. It exists in both synthetic (MK-4, or menaquinone-4) and natural (MK-7, or menaquinone-7) forms. Most Americans get enough vitamin K from their diet (NIH, n.d.). Vitamin K deficiency is rare in the United States, although the level of vitamin K consumption is steadily declining (Vermeer, 2012), and vitamin K isn’t found in the highly processed foods that are staples of the American diet.
Vitamin K2’s role in heart health
Vitamin K2 may reduce the risk of cardiovascular disease by reducing calcium buildup in arteries around the heart.
In the Rotterdam Study, scientists looked at the vitamin K1 and K2 intake of 4,807 Dutch women and men older than 55 over a 10-year period. They found that Vitamin K2 intake (of about 25 μg/day) reduced the risk of dying from heart disease by 57%. It also reduced cases of coronary heart disease by 41%, severe arterial calcification by 52%, and overall mortality by 36% (Grober, 2015). (Meanwhile, vitamin K1 was found to have no effect on heart disease or mortality).
Another study of more than 16,000 women found that vitamin K2 intake was associated with a lower risk of coronary heart disease (Gast, 2009).
One caveat: These are observational studies, not controlled studies, so they only suggest a connection; they can’t prove cause and effect in terms of the role of vitamin K2 in cardiovascular disease.
Additional health benefits of vitamin K2
Vitamin K2 may prevent osteoporosis
Bone is a living substance that is continually being created and destroyed. Vitamin K2 helps the body move calcium out of the blood and into the bone (Maresz, 2015). So it’s critical to bone health throughout life. But as we age, more bone may be lost than it is replaced, leading to an increased risk of fractures. However, some studies suggest that vitamin K2 might be protective on that front.
A meta-analysis of 13 controlled studies looked at how taking a vitamin K2 supplement (15 to 45 milligrams of MK-4 daily) affected bone density and the rate of fractures. Vitamin K2 reduced the risk of vertebral fractures by 60%, hip fractures by 77%, and non-vertebral fractures by 81% (Schwalfenberg, 2017).
In another study, postmenopausal women who ate the most natto, a Japanese dish made from fermented soybeans and the richest food source of vitamin K2, experienced less bone loss over time (Ikeda, 2006).
Keep in mind that K2 may prevent osteoporosis — the Food and Drug Administration (FDA) hasn’t issued a recommendation on that. The NIH says that the evidence on vitamin K2 and osteoporosis prevention is unclear and that more human studies are needed.
Vitamin K2 may support dental health
Vitamin K2 activates osteocalcin, a protein that’s critical to bone metabolism and maintaining the strength of teeth. Osteocalcin stimulates the growth of new dentin, the calcified tissue that lies below tooth enamel. It’s hypothesized that vitamin K2 might also guard against tooth decay (Southward, 2015).
Vitamin K2 may fight cancer
One study of nearly 25,000 people found that consuming vitamin K2 through diet was associated with a lower risk of cancer in men (but not women). Cases of prostate and lung cancer were reduced in those who consumed the highest levels of vitamin K2 (Nimptsch, 2010).
Another observational study of 11,000 men found that a high vitamin K2 intake was associated with a 63% lower risk of advanced prostate cancer (Nimptsch, 2008).
How to get enough vitamin K2
If you want to increase your intake of vitamin K2, the best way is through food. Dietary sources of vitamin K2 include meat (particularly dark chicken meat and liver), egg yolks, dairy products (like cheese, butter, and yogurt), and natto, a traditional Japanese dish made from fermented soybeans.
You can also get vitamin K2 through supplements. It’s available in multivitamins, vitamin K supplements, and formulations that are vitamin K2 alone.
According to the National Institutes of Health, an adequate daily intake of Vitamin K (both 1 and 2) is 120 mcg for men and 90 mcg for women. An upper tolerable limit hasn’t been set, but taking it in high doses is not recommended.
Side effects and potential risks of vitamin K2
Vitamin K can interact with some medications, including the anticoagulant warfarin (brand name Coumadin). Warfarin works by inhibiting an enzyme that activates vitamin K, which reduces the ability of the liver to make clotting factors. Taking increased doses of vitamin K can decrease the effectiveness of warfarin and make your blood more likely to clot, which can increase the risk of heart attacks, strokes, and pulmonary embolism. Certain medications can also reduce vitamin K absorption in the body, including antibiotics and the weight-loss drug Orlistat. Talk with your healthcare provider about all medications and dietary supplements you’re taking before you start vitamin K2 supplementation.