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Vitamin K

A Danish scientist working with hemorrhagic disease of newly hatched chickens first discovered Vitamin K in 1935. The "K" comes from the Danish spelling of "koagulation." (1) There are three forms of vitamin K, about which there appears to be some confusion in the literature. Names such as phylloquinone, phytonadione, menaquinone, menatetrenone, menaphthone and menadione are more confusing than helpful. So, for present purposes they will be identified as:

* Natural vitamin K derived from plants

* Natural vitamin K synthesized in the bowel by bacteria

* Synthetic (pharmaceutical) vitamin K

One of the most abundant sources of plant-derived vitamin K is green vegetables, since chlorophyll is high in vitamin K. Thus, the greener the vegetable, the more chlorophyll it contains. Plant-derived vitamin K is fat soluble, therefore its absorption in the intestine is facilitated by the presence of bile and pancreatic juices. Natural chlorophyll is also fat-soluble, but preparations of it available as supplements are water-soluble, making it more rapidly digestable. Tomatoes, meat, egg yolks, milk, and vegetable oils are also good dietary sources of vitamin K, but hydrogenation decreases the content of vitamin K in vegetable oils and is best avoided for this reason and because hydrogenation increases the ratio of trans-fatty acids, known to promote atherosclerosis among other pathologic conditions. Although vegetable oils contain vitamin K, an excess of fat in the bowel will bind vitamin K, decreasing its absorption.

Commensal bowel bacteria synthesize another form of vitamin K. Therefore, healthy intestines are necessary to insure an adequate supply of this form of vitamin K. Broad-spectrum antibiotics can decrease vitamin K levels, by killing off these beneficial bacteria and diminishing vitamin K production in the bowel.

All forms of vitamin K require processing by the liver before they are effective. Hence, compromised liver function can also cause a deficiency of vitamin K in the body.

Drugs that can impair blood coagulation through the vitamin K pathway are aspirin, some antibiotics, bile acid sequestrants, laxatives, orlistat, phenytoin, and, of course, warfarin. Aspirin, antibiotics, bile acid sequestrants, laxatives, and orlistat all interfere with intestinal absorption of vitamin K. Aspirin also inhibits another component of blood coagulation, platelet adhesion, thereby increasing the risk of bleeding when prothrombin levels are low. Other drugs such as phenytoin interferes with the body's ability to use vitamin K at another stage in its metabolism. Warfarin (Coumadin[R]) reduces the body's ability to synthesize prothrombin, directly antagonizing the effect of vitamin K.

Mechanisms of action in bone

Vitamin K functions as a cofactor for the enzyme that catalyzes the carboxylation of osteocalcin. (2) Osteocalcin or BGP (bone gla protein) is found exclusively in bone tissue, accounting for 10-20% of the noncollagenous protein in bone. It is a protein produced by osteoblasts and thought to be involved in calcium ion and hydroxyapatite binding. (3) Although the exact function of osteocalcin is not yet understood, it, and therefore, vitamin K, is clearly necessary for normal bone metabolism. As with most metabolic processes, a number of distinct elements are involved, so that calcium, trace elements and a variety of vitamin and endocrine agents all are necessary for normal function. This is the generally accepted explanation for the fact that nutritional elements are best acquired through natural food sources rather than as purified and isolated entities. The matrix from which vitamin K (or any other nutrient) is derived--that is, its complex found in food--is likely to be more effective than the isolated molecule.

Research studies

Two recent studies from Japan found vitamin K essentially equivalent to the biphosphonate etidronate in reducing osteoporotic vertebral fractures and in improving bone mineral density. (4,5) These results substantiate population studies from the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, the Framingham study and the Nurses' Heart Study. One USDA study of the Framingham population found a strong correlation between hip fractures in elderly men and women and vitamin K intake. (6) A second USDA study found bone mineral density (BMD) to be directly related to vitamin K intake in 1500 women, but not in men. In this study vitamin K intake varied between [micro]g and 309 [micro]g daily. Although BMD does not necessarily correlate with the incidence of hip fractures, (5) it is a common measurement of the severity of osteoporosis.

In the Nurses' Heart Study, a 10-year follow-up of 72,327 women between 38 and 63 years of age found that low intakes of vitamin K were associated with an increased risk of hip fracture in women. (7)

Conclusion

The science of nutrition and nutritional supplements continues to gain insights into safe and effective ways to improve health through food. Most of this information comes from a combination of population studies and laboratory investigations, since controlled clinical trials in humans are difficult, given the complexities of nutrition and the difficulties in establishing control groups and limiting variables. Nevertheless, all recommendations that proceed from this body of knowledge are safe, so that accumulated information can, early on, reach a stage where implementation is reasonable and desirable. What is lost in the conclusiveness of research findings is more than compensated for in the safety of the emerging recommendations.

A carefully planned menu, taking into account all that is currently known and surmised about the benefits of healthy eating, takes on a remarkably consistent picture--that of natural food products, refined and processed as little as possible to remove contaminants, and weighted strongly in favor of plant products. Further improvements identify subgroups, like olive oil and green vegetables, that have specific nutritional benefit.

Such is now the case for a planned increase in natural, plant-derived vitamin K in the human menu. Benefits to bone health, as well as blood integrity, are now convincing enough to recommend natural, plant-derived vitamin K in nutritional regimens. It is, in addition, worthy of note that many of the same foods that are rich in vitamin K have other nutritional benefits. It is to be expected and serves only to emphasize the integrity of the science of natural nutrition.

References

1. Nick, G. Key lipophilic compounds found in chlorophyll and wheat germ: Preventing spontaneous abortion and miscarriage in at-risk women. WFNJ 2001 1(2): 27-30.

2. Shearer Role of vitamin K and Gla proteins in the pathophysiology of osteoporosis and vascular calcification. MJ. Curr Opin Clin Nutr Metab Care 2000 Nov;3(6): 433-8.

3. .com/Products/BoneHealth/Research

4. Iwamoto J, Takeda T, Ichimura S. Effect of menatetrenone on bone mineral density and incidence of vertebral fractures in postmenopausal women with osteoporosis: a comparison with the effect of etidronate. J Orthop Sci. 2001;6(6): 487-92.

5. Ishida Y, Kawai S. Comparative efficacy of hormone replacement therapy, etidronate, calcitonin, alfacalcidol, and vitamin K in postmenopausal women with osteoporosis: The Yamaguchi Osteoporosis Prevention Study. Am J Med. 2004 Oct 15;117(8):549-55.

6. Booth SL, Tucker KL, Chen H, Hannan MT, Gagnon DR, Cupples LA, Wilson PW, Ordovas J, Schaefer EJ, Dawson-Hughes B, Kiel DP. Dietary vitamin K intakes are associated with hip fracture but not with bone mineral density in elderly men and women. Am J Clin Nutr. 2000 May;71(5):1201-8.

7. Feskanich D, Weber P, Willett WC, Rockett H, Booth SL, Colditz GA. Vitamin K intake and hip fractures in women: a prospective study. Am J Clin Nutr. 1999 Jan;69(1):74-9.

by Gina L. Nick, PhD, ND

Chief Scientific Officer at Longevity Through Prevention, Inc.

Phone: 866-587-4622 X702 * Fax: 866-587-4622 * E-mail:

. Box 6936 * Laguna Niguel, California 92677 USA

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