Vitamin K2 Steps Into the Spotlight for Bone and Heart Health

John Watson; Reviewed by: Anya Romanowski, MS, RD


October 10, 2018

Since its discovery nearly 90 years ago, vitamin K has enjoyed the uncomplicated status of an essential nutrient, respected but somewhat overlooked. Guidelines advised that we get our daily recommended intake of vitamin K (120 µg for men and 90 µg for women[1]) but most likely made no mention that it exists in two variants, K1 and K2.

Beginning in the 21st century, however, researchers started closely scrutinizing the structural differences between K1 and K2, which before had been considered largely irrelevant.[2] Their work has indicated that K2 may deserve special consideration as a treatment for osteoporosis and cardiovascular disease.

How Do Vitamins K1 and K2 Differ?

The umbrella term vitamin K actually describes a family of fat-soluble compounds. The body has limited ability to store the vitamin and amounts are rapidly depleted without regular dietary intake.

Vitamin K1, also known as phylloquinone, is primarily found in green leafy vegetables. K1 accounts for approximately 90% of daily vitamin K consumption in the United States.[3]

Vitamin K2, also known as menaquinone (MK), is primarily bacterial in origin. K2 is mostly encountered in fermented foods, meats, and dairy products.[4] It is further subgrouped based on the length of its side chains, from MK-4 to MK-13.[4,5] For example, meat products typically include the MK-4 variants, whereas the traditional Japanese vegetarian dish natto, made from fermented soybeans, contains MK-7, which provides the highest known vitamin K activity. K2 can also be produced by the human gut's microbiome, though the absorption and transport of K2 produced in this manner is less understood.[1]

K2 comes to us primarily through products derived from animals, who can synthesize it from the K1 they ingest from eating grass. As agricultural practices have shifted animals away from grassy pastures toward grains, K2 levels have decreased.[2] Because K2 is usually present in only modest amounts, and even less so in low-fat and lean animal products, many Western diets are inadequate providers of a nutrient researchers consider increasingly important.


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