With so much attention on other nutrients (hello, omega-3s and vitamin D), vitamin K probably isn’t even on your nutritional radar. But the latest research shows that this stealth nutrient can greatly reduce disease risk.
Vitamin K—found in leafy greens, cheese, and natto (a dish made from fermented soybeans)—is best known for its essential role in blood clotting. “Without vitamin K we would bleed to death in ten minutes from a large cut,” says Cees Vermeer, PhD, of Maastricht University in the Netherlands. Therein lies the catch. Although vitamin K is safe for most people—and is routinely given to newborn babies (who are not born with enough)—if you’re taking a blood-thinning drug, it’s dangerous to use a vitamin K supplement without a physician’s close supervision. This is because blood-thinners, such as Coumadin (warfarin), target the mechanism by which vitamin K works, so it could be unsafe to take them both at the same time.
Three kinds of K.
You might find yourself confused by vitamin K supplements because there are three forms to choose from: vitamin K1 (called phytonadione or phylloquinone) and two forms of K2: MK-4 (menatetrenone) and MK-7 (menaquinone). All three offer health benefits, usually specific to each type. And although studies have compared K1 and K2, no human studies have compared the effects of the two types of K2, says Vermeer, one of the world’s top vitamin K experts.
Vitamin K is a fat-soluble nutrient, so it’s best to take it with a little food, even if it’s just a spoonful of nut butter. Also keep in mind that vitamin K1 and the MK-4 form of K2 break down within a few hours, whereas the MK-7 form of K2 lasts in the bloodstream for days. Discover three of K’s key benefits to see if you should consider taking it.
Your body needs vitamin K to activate osteocalcin—a protein that incorporates calcium into bone; if you don’t get enough, bones won’t develop normally. A recent study showed that combining vitamin K1 with vitamin D and genistein (a soy extract) reduced the risk of bone breaks in postmenopausal women. Another three-year study found that MK-7 supplements prevented bone loss. And very large daily doses of MK-4 have been shown to reverse the symptoms of osteoporosis. If you’re at risk for osteoporosis, your best option could be a combination supplement with all three K’s.
Dose: 180 mcg MK-7 or 5,000 mcg K1 or 5,000–45,000 mcg MK-4, daily
Balances blood sugar.
Vitamin K helps regulate blood sugar levels. Research shows vitamin K-dependent osteocalcin does double duty as a hormone—regulating the number of insulin-producing cells in the pancreas. Several human studies have found that vitamin K1 supplements improve glucose tolerance.
Dose: 500 mcg K1 daily
Reduces heart calcification.
Your body uses vitamin K to make a protein that helps regulate where calcium gets deposited. With adequate vitamin K, the body moves calcium to the bones (where it’s needed) and out of the heart’s arteries (where it’s not needed). According to research, both K1 and MK-7 seem to prevent or reverse arterial calcification, which is also known as hardening of the arteries. This could be most beneficial for the elderly and people with chronic kidney disease or diabetes because of their higher risk of heart health problems, says Vermeer.
Dose: 500 mcg K1 or 50–150 mcg MK-7 daily
Our vitamin K supplement picks
Think you might benefit from taking vitamin K as a supplement?
First, talk with your health practitioner to make sure it's the right move. Then keep an eye out for our picks (below) on the shelves of your local natural retailer.
Carlson Vitamin K2 (MK-4)
This supplement delivers a hefty 5mg (5,000 mcg) of vitamin K2 in MK-4 form.
Jarrow Formulas MK-7 (Vitamin K2)
Each softgel contains 90 mcg of MK-7.
Nature's Life Vitamin K1
Few K1 supplements use the "natural" phylloquinone form, but this one does; 1,000 mcg per capsule.
Nutricology Full Spectrum Vitamin K
This high-potency supplement provides all three forms of supplemental vitamin K: 1,000 mcg K1 (phytonadione), 3,000 mcg K2 (MK-4), and 50 mcg K2 (MK-7).