Nutrition & bone health
Vitamin K: the overlooked bone builder and heart protector
by 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
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 with 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
- 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 K 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 vegetables and K2 is
produced by bacteria.
Dark green leafy vegetables and fermented foods are high in Vitamin K. 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 optimum 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 K 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 K 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 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 K, or discuss vitamin K supplementation with your health professional.
A note of caution: Those taking medications to thin the blood, such as Coumadin,
should avoid use of 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.
Collard greens, cooked
Turnip greens, cooked
Beet greens, cooked
Mustard greens, cooked
Brussels sprouts, cooked
Dandelion greens, cooked
Parsley, 10 sprigs
Lettuce, boston and bibb, raw
Lettuce, green leaf, raw
Reference: USDA National Nutrient Database for Standard Reference, Release 16
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Original Publication Date: 01/01/2009
Principal Author: Dr. Susan E. Brown, PhD