It is estimated that one in five women over the age of 50 in the United States has osteoporosis, a common bone disease that involves a loss of bone density, resulting in thin, brittle bones that break easily. Many nutritional factors are known to affect bone health, such as calcium, vitamin D and phosphorus, but recent studies have shown that vitamin K also plays an important role in maintaining strong bones.
The Role of Vitamin K in Bone Health
Vitamin K is needed for three proteins involved in bone health to work correctly. In all three of these proteins, vitamin K acts as a helper molecule that allows the protein to undergo a structural change from one form to another. The form of the protein after it has undergone a chemical reaction with vitamin K ithe form the protein must be in to strengthen bones. The three proteins crucial to bone health that interact with vitamin K are osteocalcin, matrix gla protein and protein S.
Osteocalcin
Once the protein osteocalcin has reacted with vitamin K, it has the right shape and form to bind with calcium. This second form of osteocalcin is called carboxyalted osteocalcin. Though research is still being done, many scientists think that the ability of carboxylated osteocalcin to join with calcium allows the insides of the bones to build calcium-containing bridges from one side of the bone to the other and that these bridges give bones their strength. A study conducted by Japan's Yamaguchi University School of Medicine published in the Journal of Bone and Mineral Metabolism in 2001 showed that people with higher amounts of osteocalcin had lower rates of osteoporosis.
Matrix Gla Protein and Protein S
Scientists think that after the second protein, matrix gla protein, has interacted with vitamin K, this protein helps the bone know where to put calcium, so that your bones stay strong while other parts of your body, like muscles or tendons, do not get too much calcium. Less is known about the third protein, protein S, but a study conducted by Edouard Herriot Hospital in Lyon, France, published in the medical journal Endocrinology in 1992 showed that people who do not have enough of the form of protein S after it has interacted with vitamin K have a higher risk of osteopenia. Osteopenia can be thought of as pre-osteoprosis, where your bones have less density than they should but are not to the point of being osteoporotic.
Sources of Vitamin K
A study published in the American Journal of Clinical Nutrition in 1999 demonstrated that women who consumed low levels of vitamin K were more likely to develop osteoporosis. Your body is able to make some vitamin K in your colon, although you still need to include vitamin K in your diet. Adequate intake of vitamin K is 120 micrograms (mcg) a day for men who are over 18 years old and 90 micrograms a day for women over 18. Green, leafy vegetables are a great source of vitamin K: A quarter cup of chopped raw kale has 135 mcg, a half cup of raw spinach has 70 mcg and a cup of shredded leaf lettuce has 60 mcg. Vitamin K can also be found in other foods, such as canola oil, which has 25 mcg per tablespoon, and broccoli, which has 220 mcg per cup. As with any change to your diet, you should first ask your doctor or dietitian about whether you should increase the amount of vitamin K you are getting. Though talking with your doctor is important for everyone, it is especially important if you are on heparin, warfarin, Coumadin or any other blood thinner.
References
- Pub Med Health: Osteoporosis
- Pub Med.gov: Journal of Bone and Mineral Metaboism; Carboxylation of Osteocalcin May Be Related to Bone Quality; T. Suqiyma and S. Kawai; 2001
- Pub.med.gov: Endocrinology; Protein-S, a Vitamin K-Dependent Protein; C. Maillard et al; 1992
- Journal of Biological Chemistry; Matrix GLA Protein, a Regulatory Protein for Bone Morphogenetic Protein-2; A. Zebboudj, et al; 2001
- American Journal of Clinical Nutrition; Vitamin K Intake and Hip Fractures in Women; D. Feskanich et al; 1999
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