Nutrition & bone health

Vitamin K: the overlooked bone builder and heart protector

Dr. Susan E. Brown, PhDBy Dr. Susan E. Brown, PhD

At the Center for Better Bones, we have long noted the trend towards increased arterial calcification with the use of high-dose calcium supplementation when given without other key bone nutrients. We propose that these trends are strongly related to vitamin K status, particularly to inadequacy of the menaquinone-7 (MK-7) form of vitamin K2.

Vitamin K is essential for the proper formation and full activation of the Gla proteins. The Gla protein osteocalcin, when fully carboxylated by vitamin K, allows for the binding of calcium to the bone matrix. The Gla protein known as matrix-Gla protein is found in vascular smooth muscles. Matrix Gla protein is a key inhibitor of soft tissue calcification that binds calcium, preventing it from depositing in the vessel walls. Both Gla proteins are essential for proper calcium metabolism, and neither can be fully activated without adequate vitamin K.

These assertions are supported by a wide range of clinical data; for example:

  • It is well known that vitamin K antagonists such as warfarin double arterial calcification in humans.
  • The decade-long, 4800-person Rotterdam study documented that people who consumed the most vitamin K2 have a 50% reduced risk of arterial calcification. They also exhibited a 50% reduced risk for cardiovascular events during this 10 year period.
  • In 2009, a 16,000-person study by Gast and colleagues showed that high intake of natural vitamin K2, but not vitamin K1, protected from cardiovascular disease. This study reported that for every 10 mcg vitamin K2 consumed, the risk of coronary heart disease was reduced by 9%.
  • A recent animal study by Schurgers and colleagues (2006) showed regression of warfarin-induced arterial calcification when given adequate supplemental doses of vitamin K2.

As it appears vitamin K, and vitamin K2 as MK-7 in particular, plays an important role in keeping calcium in the bones and out of the arteries. Hopefully, as we cast a broader net of understanding, clinical bone trials will include analysis of vitamin K status along with calcium intake evaluation.

Vitamin K: the best food sources

Vitamin K is not a single nutrient, but the name given to a group of vitamins of similar composition. The two main groups of vitamin K that occur naturally are vitamin K1 (phylloquinone) and K2 (menaquinone). K1 is found in many dark green leafy vegetables and K2 is produced by bacteria in fermented foods.

While you probably have enough vitamin K to provide for normal blood clotting, you most likely do not consume enough vitamin K to allow for optimal bone health. For example, studies document that for optimization of the bone protein osteocalcin adults would do well with a daily K1 intake of 1000 mcg. Currently the average K1 intake in this country is only 75 to 125 mcg.

The table below lists the foods highest in vitamin K1. It is worth noting that the absorption of vitamin K1 from vegetables is likely enhanced by the presence of dietary fat in the same meal, just as occurs with two other fat-soluble vitamins, vitamins D and E. Unless you are a “greens” lover, you might find it difficult to consume 1000 mcg of vitamin K in foods. Take heart and do the best you can. The prestigious Framingham Heart Study found that those with the highest vitamin K1 intake (250 mcg/day in this study, compared to the recommended intake of about 75 mcg/day) had a threefold reduction in hip fracture risk. Even if your vitamin K1 intake is lower than 250 mcg a day, you can also note that the 72,327-person Nurses’ Health Study found that those consuming a mere 109 mcg vitamin K1 a day had a lower risk of hip fracture over a ten year period than those consuming less vitamin K1.

Vitamin K2 is the most biologically active form of vitamin K. It is also the most beneficial for bone health maximization. Vitamin K2, however, is produced by bacteria and is mainly found in fermented foods such as ripe cheese, yogurt and a fermented soy food known as natto. Having a very strong odor, natto is often called the “Limburger cheese” of Japan. Natto is by far the best food source for Vitamin K2.

Vitamin K3 (menadione) is a synthetic form that is manmade and not recommended for use as a nutritional supplement.

Foods containing vitamin K1 and K2 are nutritious and increasing their intake can provide many health benefits. If you suspect your vitamin K intake is low, you can also use vitamin K1 and K2 supplements. Studies, in fact, suggest that the absorption of K1 from a tablet is considerably higher than the absorption from vegetables. You might use the following table to determine if your intake of vitamin K1 reaches the optimum level of 1000 mcg a day. If you fall short, consider increasing consumption of foods high in vitamin K1, or discuss vitamin K1 supplementation with your health professional. Vitamin K2 supplements, particularly as MK-7, are highly absorbed and long lasting in the body.

A note of caution: Those taking medications, such as Coumadin, to thin the blood should avoid use of all supplemental vitamin K as it can reverse the effects of this medication. Also, those on this medication should consult with their physician before increasing consumption of foods high in vitamin K.

RDA 70-140

Mcg Vit. K1 per 1/2 cup

Kale, cooked
Collard greens, cooked
Spinach, cooked
Turnip greens, cooked
Beet greens, cooked
Mustard greens, cooked
Brussels sprouts, cooked
Broccoli, cooked
Dandelion greens, cooked
Parsley, 10 sprigs
Lettuce, boston and bibb, raw
Asparagus, cooked
Lettuce, green leaf, raw
Lettuce, romaine

Reference: USDA National Nutrient Database for Standard Reference, Release 16

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Original Publication Date: 01/01/2009
Last Modified: 07/11/2014
Principal Author: Dr. Susan E. Brown, PhD