Vitamin K Builds Strong Bones

Making sure a woman's diet contains adequate amounts of vitamin K may help prevent bone loss, according to a new study in the American Journal of Clinical Nutrition (2003;77:512–6). This study supports previous research indicating that low dietary vitamin K intake is associated with an increased risk of hip fracture.

In the new study, vitamin K intake was assessed, using a food-frequency questionnaire, in 1,112 men and 1,479 women (average age, 59 years). Among the women, those consuming the least amount of vitamin K (25th percentile or lower) had significantly lower bone mineral density of the hip and spine, compared with women consuming the most vitamin K (75th percentile or higher). Among the men, there was no association between vitamin K intake and bone density.

While vitamin K is best known for its role in blood clotting, this vitamin also plays a key role in bone formation. Vitamin K is required for the production of a structural protein in bone called osteocalcin, which serves as the matrix upon which mineral crystals form in the process of laying down new bone. Without adequate vitamin K, osteocalcin cannot be produced, and bone formation becomes impaired.

Studies have shown that women with osteoporosis have significantly lower blood levels of vitamin K, compared with women of the same age who have normal bones. In addition, when women with osteoporosis take supplemental vitamin K, the urinary excretion of calcium falls by about 50%, suggesting that less calcium is being leached from the bones.

The recommended dietary allowance (RDA) for vitamin K is 1 mcg per 2.2 pounds of body weight per day, or approximately 70 mcg per day for an average sized person. Some research, however, suggests that the optimal level of intake may be higher, as much as 400 mcg per day. A typical western diet contains 80 to 150 mcg per day. Foods rich in vitamin K include lettuce, leafy green vegetables, and certain edible oils (soybean, canola, cottonseed, and olive oil).

Osteoporosis is a condition in which the bones become thin and porous, thereby increasing the risk of fractures. As many as 30% of postmenopausal women in the United States develop osteoporosis, and the condition is responsible for approximately 1.2 million fractures per year. Osteoporosis is far less common in men than in women, although as men approach 80 years of age, the prevalence of thin bones becomes similar to that in women.

In addition, to vitamin K, a number of other nutrients play a role in keeping bones healthy and preventing osteoporosis; these include vitamin D, vitamin B6, folic acid, zinc, copper, manganese, silicon, boron, strontium, and vitamin C.

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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