When you think of vitamins, you probably start at the beginning of the alphabet. A, B, C—you get the picture. But something weird happens after vitamin E: We skip straight to vitamin K.
Always the bridesmaid, never the bride, vitamin K has long been considered last—and least. Yet despite its lack of limelight, K is still important for your health.
For starters, there are actually two types of this fat-soluble vitamin: vitamin K1 (a.k.a. ‘phylloquinone’), which supports blood clotting after injury, and vitamin K2 (a.k.a. ‘menaquinone’), which promotes strong bones and a healthy heart. The bacteria in our gut produce some vitamin K2, and we get the rest of our Ks from food.
Wound healing. “Without the clotting benefit of vitamin K1, a simple paper cut could cause massive bleeding,” says Maria Zamarripa, M.S., R.D., owner of FoodFarmacistRD. Why? Our bodies need vitamin K to produce the proteins that help blood clot. That’s why it’s used when a patient on prescription blood thinners experiences an uncontrolled bleeding incident, and is even given to newborns who don’t yet have enough vitamin K in their bodies for proper blood clotting, according to the U.S. National Library of Medicine.
Strong bones. Ever wonder why you see K2 in bone support supplements? “K2 can boost bones’ absorption and utilization of calcium,” says Zamarripa. This supports stronger bone density, which is key in preventing osteoporosis, fractures, and injury as we age. In fact, one study found that postmenopausal women with osteoporosis who took 45 milligrams of vitamin K2 with 1,500 milligrams of calcium per day saw a significant increase in lumbar bone mineral density.
Heart health. Because vitamin K2 activates an enzyme that shuttles calcium into the bones, it also promotes heart health by preventing calcium from building up in the arteries, says Zamarripa.
How Much K Do You Need?
This is where things get a little confusing. The National Institutes of Health (NIH) recommends 90 micrograms of total vitamin K per day for women and 120 micrograms per day for men. However, since testing vitamin K levels (particularly K2) is difficult and there’s not enough data to determine how much K is best for most people, this recommendation is based only on the K1 levels already seen in healthy people
That’s why the research organization VitaminK2.org believes that the current recommendations are insufficient for the optimal function of the proteins in our tissues (like bones and blood vessels) that depend on vitamin K. “Our concern is that there is a current RDA for K1, but none for Vitamin K2—so the population is not receiving its bone and cardiovascular benefits,” says Katarzyna Maresz, Ph.D., President of the International Science and Health Foundation, the independent international research consortium that created VitaminK2.org.
For now, the NIH asserts that vitamin K is only of concern for people who take blood thinners or have bleeding disorders—but Maresz’s organization suggests it’s also important for newborns, children, adults over 40, and people with kidney issues, intestinal disorders (like IBS), and cystic fibrosis, who may all be lacking in that bacteria-produced K2.
The organization also posits that the typical Western diet contains insufficient amounts of vitamin K2—an issue that’s only worsened by our frequent use of antibiotics, which “can kill the good bacteria in our gut, potentially reducing our vitamin K2 levels,” Zamarripa says.
How To Up Your Intake
You’ll find the more-common vitamin K1 in dark leafy greens and cruciferous vegetables, such as kale (531 micrograms per cooked half cup), spinach (444 micrograms per cooked half cup), broccoli (220 micrograms per cooked cup), Brussels sprouts (219 micrograms per cooked cup), and Swiss chard (299 micrograms per raw cup).
The elusive vitamin K2, meanwhile, is found in pasture-raised animal products such as full-fat dairy, egg yolks (six micrograms per egg), and ground beef (six micrograms per three-ounce serving). It also has another lesser-known, more potent source: a Japanese dish called ‘natto,’ which is made from fermented soybeans and packs a whopping 850 micrograms per three-ounce serving. A study of elderly Japanese men even links habitual intake of natto—and its vitamin K2—with increased bone health.
To make sure you’re gettinbg adequate K2, Maresz recommends taking a high-quality K2 supplement—45 micrograms a day for children and 180 micrograms a day for healthy adults. And, “if your doctor prescribes antibiotics, make sure eat plenty of dark leafy green vegetables and fermented dairy products like yogurt, or take a supplement, to replenish your vitamin K,” says Zamarripa, (We like The Vitamin Shoppe brand 100mcg Vitamin K2.)
Since vitamin K can affect the effectiveness of blood thinners, talk with your doctor before adding a supplement—or even more leafy greens—to your routine if you’re on medication.