Are You Getting Enough Vitamin K?

For years, vitamin K has been the neglected stepchild in the world of nutrition, while vitamins C, D, E, beta-carotene, and others grabbed all the attention. That is until groundbreaking research propelled vitamin K into the limelight.

Dutch researchers discovered very strong links between vitamin K intake, arterial calcification, and cardiovascular death. In this clinical trial of nearly 5,000 older Dutch men and women, known as the Rotterdam study, participants with the highest consumption of vitamin K had a 50 percent reduction in arterial calcification and death from cardiovascular disease, and a 25 percent decline in overall mortality.

But which type of vitamin K should you take? Vitamin K is actually a group of fat-soluble compounds divided into two primary groups: K1 and K2, and they’re not exactly the same. K1 is abundant in broccoli, kale, chard, and other leafy greens; there’s also a little in olive and vegetable oils. K2 is found in fatty meat, egg yolks, and fermented products such as cheese, sauerkraut, and natto (by far the richest source), plus it is synthesized by bacteria in the large intestine. Although Americans get more dietary K1, it’s poorly absorbed. K2, on the other hand, is taken up rapidly.

These two types of vitamin K also have somewhat different physiological actions. K1 is more active in clotting, while K2 is the preferred form in the soft tissues and bones. In the Rotterdam study mentioned above, vitamin K2 intake reduced risk of arterial calcification, heart attack, and death, while K1 consumption had no protective effect.

Because supplemental vitamin K comes in various forms, reading labels can be confusing. Vitamin K1 is often listed as phytonadione or phylloquinone. Vitamin K2, also called menaquinone, comes in two forms: MK-4 and MK-7. The preferred form for anyone taking Coumadin (warfarin) is low-dose K2 (MK-7). I do not recommend synthetic MK-4 for these patients.

The usual suggested daily dose of vitamin K2 (MK-7)—the kind we use in the clinic—is 100–150 mcg. If you have arterial disease or osteoporosis, consider taking up to 300 mcg per day. Vitamin K is safe, even at higher levels—except for those taking Coumadin. If you are taking Coumadin, talk to your doctor about taking a low dose of K2 (MK-7), approximately 45 mcg per day.

Now it’s your turn: Do you take vitamin K?

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