Bone health

Vitamin K — a healthy little secret that’s good from heart to bone

by Dr. Susan Brown, PhD

• Vitamin K prevents arterial calcification
• Foods rich in vitamin K

How often have you heard about vitamin K in the news or at your doctor’s office? My guess is not much. Many people used to say vitamin K wasn’t even a “real” vitamin, and that it simply helped us clot blood. But we’ve since learned a lot about its amazing benefits to the body, and it looks to me like we should start paying attention to this little known vitamin.

As it turns out, vitamin K plays an integral role not just in blood clotting, but — importantly for women — for bone health and heart health. Most of us have enough vitamin K to provide for normal blood coagulation, but you may need more to protect your bones and cardiovascular health. Studies suggest that women would do well with a daily K1 intake of about 1000 micrograms, yet the average intake in this country is only one-tenth that amount!

Even though calcium is the buzz word when talking about healthy bones, I’ve noticed an increased trend towards arterial calcification — hardening of the arteries — when high-dose calcium is taken without benefit of other key bone nutrients like K. So what’s a woman to do? The answer can be found in vitamin K. Let’s take a closer look at this often overlooked vitamin and explore its natural food sources. You may be surprised by how much K can do for you.

Keeping calcium in bone, not arteries

Vitamin K, specifically the vitamin K2 form known as menaquinone (MK-7), plays an important role in keeping calcium in your bones — and out of your arteries.

Acting through what’s known as a Gla protein called osteocalcin, vitamin K allows calcium to bind the bone matrix while the body is building new bone. A similar molecule known as matrix Gla protein is synthesized by vascular smooth muscle cells. In contrast to osteocalcin, matrix Gla protein prevents calcification of soft tissue, meaning it stops calcium from being deposited in the walls of your blood vessels (arterial calcification) — a very good thing for anyone worried about heart health.

Both of these Gla proteins are essential for proper calcium metabolism, and neither can be fully activated without adequate vitamin K.

These beneficial effects were observed in the prestigious Framingham Heart Study, where those with the highest vitamin K1 intake (250 mcg/day, compared to the recommended daily intake of 90 mcg/day ) had a threefold reduction in hip fracture risk. But even an intake of vitamin K1 below 250 mcg a day can be to your bones’ advantage. It was found in the 72,327-person Nurses’ Health Study that all the women consuming over 109 mcg vitamin K1 a day had a lower risk of hip fracture over a ten-year period than those consuming less than that.

The best vitamin K food sources

So how can you get enough vitamin K? Different kinds of foods contain different kinds of vitamin K, but generally, dark green leafy vegetables and fermented foods are the best sources.

For women, the current recommended daily intake (RDI) of vitamin K1 is 90 mcg, but as noted above, research suggests an intake of 1000 mcg/day could be of tremendous benefit to the bones, the blood vessels, and whole-body health. See the vitamin K table to learn which foods contain K1, and about how much you’re getting in a half-cup serving.

Vitamin K2 is the most biologically active form in terms of bone and vascular health maximization, specifically the form known as MK-7. Produced by bacteria, MK-7 is found mainly in certain cultured foods such as ripe cheese and, most notably, a fermented soybean dish known as natto. Having a characteristic strong odor, natto is sometimes called the “Limburger cheese” of Japan. Natto is by far the best food source for MK-7, but some people find it too strong for their liking. Check the vitamin K table for some other ways to get your K2.

Like vitamins A, D, and E, vitamin K is a fat-soluble vitamin, so its absorption from vegetable sources is enhanced by the presence of dietary fat in the same meal. So go ahead and drizzle olive oil onto your steamed greens, or braise them in some butter!

Food sources of vitamin K

Food Approx. K1 content (mcg/½-cup) Wakame seaweed, dried 1293 Kale, fresh, cooked 530 Collard greens, fresh, cooked 418 Spinach, fresh, cooked 445 Laver seaweed, dried 413 Turnip greens, fresh, cooked 265 Beet greens, fresh, cooked 348 Watercress, raw 315 Dandelion greens, cooked 288 Mustard greens, fresh, cooked 210 Hijiki seaweed, dried 175 Parsley, 10 sprigs 164 Broccoli, fresh, cooked 110 Brussels sprouts, fresh, cooked 109 Onions, spring or scallions, raw 103 Curry powder 93 Asparagus, frozen, cooked 72 Lettuce, green leaf, raw 35 Lettuce, Cos or romaine, raw 28 Sauerkraut 25 Soybeans, fresh, cooked 15 Lettuce, butterhead (Boston or Bibb), raw, 1 leaf 8 Lettuce, iceberg, raw 6

Food Approx. K2 content (mcg/100 g —3.5 oz., or ½-cup) MK-4 MK-7 Natto (fermented soybeans) 2 939 Goose liver paste 369 Hen’s eggs, yolk, raw 64 Chicken, thigh, raw 27 Butter 21 Mayonnaise, whole egg 17 Beef, chuck, raw 15 Cream 8 Hen’s eggs, whole, raw 7 Pork, thigh, raw 6 Curry powder Processed cheese 5 0.3 Yogurt, whole milk, plain 1 0.1

References

Not a fan of greens or slippery beans?

Daily replenishment of vitamin K1 is important because reserves in your liver turn over quite quickly. There is evidence that vitamin K2 is produced by friendly bacteria in our lower intestines, but we don’t really know to what extent this K2 gets absorbed and contributes to your body’s daily demands. What we can deduce is that if intestinal bacteria were supplying us with all the K our bodies required, osteoporosis and cardiovascular disease in women would not be so widespread today.

But unless you are a lover of seaweed, greens, or fermented beans, you might find it difficult to consume enough vitamin K from food each day. Take heart and do the best you can. If you suspect that your vitamin K intake is low, you can also use vitamin supplements. Though it seems to run counter to everything we believe about a whole foods diet, studies suggest that in the case of vitamin K, absorption from a tablet is considerably higher and faster than it is from vegetables.

Check the tables above to see if your intake is high enough. If you fall short, add foods high in vitamin K to your grocery list right now. If the health of your bones and blood vessels are of concern to you, discuss vitamin K supplementation with your health professional.

If you’re taking medications to thin the blood, such as Coumadin, don’t take supplements containing any form of vitamin K without careful monitoring from your physician. Also be sure you consult with your practitioner before suddenly increasing consumption of K-rich foods. In recent research, evidence is emerging that K2 is the form that provides maximal protection with the fewest side effects — but remember, if you’re on blood thinners, you’ll still need regular monitoring in follow-up.

Nutrients in harmony

I use the synergistic connection between calcium and vitamin K as a potent reminder that vitamins and minerals work best for our bodies when they are taken together. Bone health is not just about calcium or vitamin D or any singular vitamin, but about a good base of nutrients working together. For more information, read my article on 20 key nutrients for bone health.

Related to this article:
References & further reading on the benefits of Vitamin K

 

Last Modified Date: 05/25/2011
Principal Author: Dr. Susan E. Brown, PhD