Older Women Need More Vitamin K
The dietary requirement for vitamin K among elderly women may be higher than the 90 mcg per day that is generally believed to be sufficient, according to a report in Journal of Nutrition (2003;133:2565–9). Failure to consume an adequate amount of this vitamin could promote the development of osteoporosis and increase the risk of fractures.
Vitamin K was so named because of its effect on blood coagulation; it is needed for the synthesis of certain proteins that cause blood to clot. Without sufficient vitamin K, blood clotting is impaired and excessive bleeding can occur. The widely used "blood thinning" drug warfarin works by interfering with the effect of vitamin K on clotting proteins.
Another important, though less known, function of vitamin K is to promote the synthesis of a protein called osteocalcin, which plays a key role in the building of bone. Through its effect on osteocalcin production, vitamin K aids in the healing of fractures and decreases the risk of developing osteoporosis.
In the new study, elderly female volunteers (average age, 70 years) were given a vitamin K-deficient diet (18 mcg per day) for four weeks, after which their vitamin K intake was progressively increased to 86, 200, and 450 mcg per day in successive two-week periods. During the vitamin K-depletion phase, the production of blood-clotting proteins and osteocalcin decreased. While the synthesis of blood-clotting proteins returned to normal after supplementation with 200 mcg per day of vitamin K, osteocalcin production remained below normal, even after the amount of vitamin K was increased to 450 mcg per day for two weeks.
This study suggests that the amount of vitamin K needed to produce healthy bones is greater than the amount required for normal blood clotting. The study also suggests that the current recommended intake of vitamin K of 90 mcg per day is not sufficient to support optimal production of osteocalcin by elderly women. Previous studies have shown that blood levels of vitamin K are often low in people with osteoporosis, and that supplementing with vitamin K may prevent bone loss. Additional research, using longer periods of vitamin K supplementation, is needed to determine what level of vitamin K intake is needed to support bone health.
The main food sources of vitamin K are vegetables such as collards, spinach, broccoli, brussels sprouts, cabbage, and lettuce. Certain oils (e.g., soybean, canola, cottonseed, and olive) also contain moderate amounts. Vitamin K is also present in some multiple-vitamin preparations. Individuals taking warfarin should not change their habitual vitamin K intake without a doctor's supervision.
Alan R. Gaby, MD, an expert in nutritional therapies, testified to the White House Commission on CAM upon request in December 2001. Dr. Gaby served as a member of the Ad-Hoc Advisory Panel of the National Institutes of Health Office of Alternative Medicine. He is the author of Preventing and Reversing Osteoporosis (Prima, 1994), and co-author of The Natural Pharmacy, 2nd Edition (Healthnotes, Prima, 1999), the A–Z Guide to Drug-Herb-Vitamin Interactions (Healthnotes, Prima, 1999), Clinical Essentials Volume 1 and 2 (Healthnotes, 2000), and The Patient’s Book of Natural Healing (Prima, 1999). A former professor at Bastyr University of Natural Health Sciences, in Kenmore, WA, where he served as the Endowed Professor of Nutrition, Dr. Gaby is the Chief Medical Editor for Healthnotes, Inc.
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