Got lettuce? Vitamin K and osteoporosis
July 20, 2011
Everybody has seen celebrities wearing a milk mustache, but nobody has seen them wearing a head of lettuce.
What’s lettuce got to do with it? Well, lettuce is a source of vitamin K, and vitamin K is of vital importance in bone health. Vitamin D is known for its ability to promote blood coagulation. It was discovered by Henrik Dam in Copenhagen in 1929 and was named vitamin K for koagulation. It was not until 1975 that vitamin K was discovered to play a role in bone formation. The first clue was reported in 1975 in a study by Pettifor and Benson published in the Journal of Pediatrics. Three women who were taking anticoagulant drugs during pregnancy gave birth to children with serious bone deformities. Anticoagulant drugs, of course, inhibit vitamin K.
The discovery of Osteocalcin
In 1976, Paul A. Price and others first described a vitamin K-dependent bone protein called osteocalcin. After collagen, osteocalcin is the most abundant protein in the bone, accounting for 15-20 percent of bone protein. It is one of the most abundant proteins in the body. Osteocalcin was so named because it is found solely in bone (osteo) and because it attracts calcium (calcin) to bone tissue. But in order to attract calcium, osteocalcin has to be carboxylated.
Carboxylation is a chemical process involving carbon dioxide and hydrogen. Vitamin K is necessary for carboxylation of osteocalcin. The level of noncarboxylated or undercarboxylated osteocalcin in the blood is a measure of vitamin K deficiency. A 1997 study by Vergnaud and others published in The Journal of Clinical Endocrinology & Metabolism found that increased levels of undercarboxylated osteocalcin predict hip fracture in elderly women, independently of bone mass. A1998 study by Szulc and others in the Journal of Clinical Investigation found a higher percentage of undercarboxylated osteocalcin in women who subsequently sustained a hip fracture. The concentration of circulating undercarboxylated osteocalcin has been reported to increase with advancing age in women, and vitamin K has been reported to return that concentration to normal.
A number of studies provide evidence for the role of vitamin K in bone health. In a ten year study (The Nurses’ Health Study) of 72,327 middle-aged and older women, published in 1999 in the American Journal of Clinical Nutrition, those women in the study with moderate and high intakes of viatmin K had a lower risk of hip fracture than those with a low intake of vitamin K. Two studies found low concentrations of vitamin K in the blood of people with osteoporosis and in elderly women with hip fractures. Two other studies found that supplementation with vitamin K increased bone mineral density and reduced fracture rates in people with osteoporosis. (Both of these studies were published in 2000 in the Journal of Bone and Mineral Re3search.) One of the most interesting studies found a correlation between calcium deposits in the arteries (atherosclerotic calcifications), low bone mass, and low vitamin K. Low vitamin K affects the mineralization processes both in bone and in atherosclerotic plaques, but in opposite ways: it causes depletion of calcium in bone, where it should be, but deposits calcium in the arteries, where it shoud not be. This article can be found in the November 1996 issue of Calicification Tissue International.
Sources of Vitamin K
Naturally occurring K vitamins can be classified into two groups: K1, the major form occurring in plants, and K2, which is synthesized by bacteria. Natural sources of vitamin K1 are green leafy vegetables such as broccoloi, Brussels sprouts, green cabbage, kale, lettuce, parsley (a particularly rich source), spinach, and watercress. Vitamin K2 can be found in cheese and some fermented foods. Intestinal bacteria also produce vitamin K2. Vitamin K deficiency may be more common now than in previous times because of overuise of antibiotics. Antibiotics destroy the friendly intestinal bacteria that produce vitamin K2. There are times when antibiotics are necessary. In that event, it is wise to supplement with probiotics, that is, friendly bacteria, to replace the good bacgteria in the gut that have been destroyed by the antibiotics. Among the most common of these probiotics are lactobacillus acidophilus and bifid bacterium bifidum.
A study published in November 2002 in the American Journal of Clinical Nutrition established that a daily intake of 1,000 micrograms or one milligram of vitamin K1 was required to maximally carboxyl ate circulating osteocalcin.
So, how about a head of lettuce?
Mary Lou Williams, M. Ed., is a lecturer and writer in the field of nutrition. She welcomes inquiries. She can be reached at 267-6480.