Vitamin K—for Kalcium

Vitamin K is a take it for granted vitamin, one that is not suspected when we talk of deficiency because it is made for us by normally occurring bacteria in our intestine and is provided normally in dark green vegetables, such as spinach, kale, cabbage and kale. It is also in peas, tomatoes, egg yolk and liver.

Blood clotting is the best-known function of the vitamin and the German scientist who discovered the vitamin gave it the name, K, as in Koagulation. That chemistry was worked out decades ago: vitamin K is a catalyst for the production of the clotting factor, prothrombin, by the liver. Deficiency, it was believed, could be adequately detected by a simple clotting test, the prothrombin time. This test is still routinely used to monitor the effect of coumarin drugs, which inactivate vitamin K and are therefore effectively used as anti-coagulants in humans. It is quite useful in detecting gross deficiency; however direct measurement of the vitamin in blood is now commercially available and this test shows low levels even when the prothrombin time is normal.

The relationship between vitamin K and calcium has been explored in the past 15 years. Skeletal birth defects were observed in babies of women treated with coumarin drugs for blood clotting in the early 70's. About the same time, a connection between osteoporosis and vitamin K was suspected, and there is a report as far back as 1960 describing delayed fracture healing cured by vitamin K.

By 1977 it was theorized that vitamin K donates a carbon-oxygen (carboxyl) fragment to glutamic acid residues, thus endowing them with a capacity to bind calcium to prothrombin, a key step in hardening of the thrombin clot. However it was not until 1979 that chemists identified a new calcium binding protein, osteocalcin, in bone. Osteocalcin contains glutamic acid residues also and it is now clear that vitamin K is required to carboxylate glutamic acid in bone just as in liver. It is by now well demonstrated that vitamin K is required both for repair and maintenance of bone as well as proper coagulation of the blood.

Calcium loss is the essential feature of osteoporosis, thinning of the bones that afflicts millions of men and post-menopausal women. It is not likely to be corrected by calcium supplements in the face of vitamin K deficiency. How common is this deficiency? A 1984 study of 15 cases of fracture of the spine or femur due to osteoporosis found serum levels of vitamin K only a third of normal (i.e. compared to a control group without osteoporosis). There is evidence that even normal people heal fractures more quickly if treated with vitamin K. Calcium loss is reduced by 20 to 50 percent in patients treated with vitamin K supplements.

Antibiotic use is probably the most common cause of deficiency and anyone taking long-term sulfa drugs for bowel disorder or tetracycline for acne should check their vitamin K status. Don't wait for backache, dowagers hump or a fractured bone to announce the diagnosis of osteoporosis. Salicylates also interfere with vitamin K and long term use of aspirin is certainly going to increase the amount of osteoporosis, particularly in men, who are lately advised to take it to prevent vascular disease. Arthritis sufferers who take salicylates for long periods of time are also at risk of decalcification and with delayed healing of the affected joints and greater deformity to the structure as a result.

Intestinal malabsorption of the vitamin is not rare, even without much use of antibiotics. Fat malabsorption in gall bladder disease or after surgical removal of the gall bladder is quite common. More sinister is depletion of vitamin K and other fat-soluble vitamins due to low fat diets. Anorexia, bulimia, weight loss programs that avoid egg, whole milk and cheese, butter, meat and use low calorie salad oils can reduce fat intake below 20 percent of Calories. The Pritikin Diet recommends a 10 percent fat diet and, in fact, the diet at the Pritikin Center is only 7 percent fat. It is known that below 5 percent fat, deficiency of vitamin K, as well as other fat soluables, such as A, D and E, is certain. I think long term adherence to such low levels of fat is unnecessary but, more to the point, also likely to aggravate calcium and bone loss.

If you fit any of these categories of deficiency, especially if you have symptoms of bruising or bone pain, you would be well advised to check your vitamin K level.

(in 1971 by Tomita (Clin Endocrinol Jpn 19,731) Nature, v 185, p 849

©2007 Richard A. Kunin, M.D.