Vitamin K is the first nutritional supplement that most Americans ever receive. That's because newborns routinely get a shot of the nutrient—which is crucial for coagulation (blood clotting)—to help prevent a severe and sometimes fatal bleeding disorder.
Discovered by a Danish scientist in 1934, the vitamin was dubbed "K" for "Koagulation" (the Danish spelling). But it wasn't until years later that scientists figured out how it works-by helping the liver manufacture several proteins that control blood clotting.
Latest development: Researchers are now discovering that vitamin K provides a wide variety of health benefits that extend well beyond blood clotting.
Vitamin K For Better Health
Vitamins C and E tend to get the most media attention, but recent findings on vitamin K's ability to help curb the development and/ or progression of certain common medical ailments are worth noting. Examples...
- Arthritis. Research shows that low dietary intake of vitamin K may play a role in the development of osteoarthritis.
Scientific evidence: In a study published in the April 2006 issue of the journal Arthritis & Rheumatism, higher blood levels of dietary vitamin K were associated with a lower risk for osteoarthritis of the hand and knee.
- Heart disease. Vitamin K aids the function of the biochemical matrix Gla-protein, which helps prevent calcium buildup in plaque-filled arteries.
Scientific evidence: Researchers in the Netherlands studied more than 4,800 people over age 55. Compared with those with the lowest intake of vitamin K, those with the highest intake were 52% less likely to have severe calcification of the aorta, the major artery leading from the heart. The participants were 57% less likely to die of heart disease.
- Liver cancer. Cirrhosis of the liver, which occurs when alcoholism or infection with the hepatitis B or C virus results in scarred, abnormal liver tissue, can lead to liver cancer.
Scientific evidence: Studies of animal and human cells show that vitamin K may help control the progression of liver cancer. For example, in a study published in the Journal of the American Medical Association, Japanese researchers divided 40 women with viral cirrhosis of the liver into two groups. One group received vitamin K daily...the other did not. Two of the women in the vitamin K group developed liver cancer, compared with nine in the non-vitamin K group. Statistically, vitamin K lowered the risk for liver cancer by 80%.
- Osteoporosis. Vitamin K aids in the formation of osteocalcin (a protein that helps calcium bind to bone). This bone-strengthening process may help prevent and/or treat osteoporosis, the brittle-bone disease that afflicts more than 10 million older Americans-80% of them women.
Scientific evidence: Scientists at Harvard Medical School analyzed data on vitamin K intake and bone health in more than 70,000 women. Those with the highest dietary intake of vitamin K had a 30% decreased risk for hip fracture compared with those who had the lowest intake. Other studies show similar results for men.
In England, researchers analyzed data from 13 Japanese clinical trials that used large, pharmacological doses of vitamin K to treat osteoporosis. Overall, the vitamin reduced the rate of spinal fractures by 40% and hip fractures by 13%.
Latest development: Scientists at the University of Toronto, Tufts University and the University of Wisconsin have completed three clinical trials to determine whether nutritional doses of vitamin K can prevent bone loss in postmenopausal women. It is likely that researchers will present or publish their results within 12 months.
Are You Getting Enough?
The US government's recommended daily intake for vitamin K is 90 micrograms (mcg) for adult women...and 120 mcg for adult men. That level is high enough to prevent vitamin K deficiency, a rare condition that can lead to impaired blood clotting.
But is it high enough to keep your blood, bones and heart healthy? That's a question nutritional scientists are asking—but haven't yet answered.
However, scientists do know an easy, natural way to maximize your intake of vitamin K. It comes down to the classic maternal advice—eat your vegetables.
*To stay abreast of this research, go to the National Institutes of Health Web site, www.clinicaltrials.gov.
Green vegetables—leafy and otherwise—are among the best dietary sources of vitamin K.
Don't have a taste for kale or spinach? Don't worry. One-half cup of broccoli sautéed in olive oil gives you plenty of vitamin K. Or try a lettuce salad (using any type except iceberg) with a teaspoon of salad dressing that contains vegetable oil (some fat is needed for absorption of vitamin K). And don't worry about cooking-it doesn't destroy the vitamin.
Among vegetable oils, the richest sources of vitamin K (per two-tablespoon serving) are soybean oil (50 mcg) and olive oil (13 mcg).
Another good source of vitamin K: Mayonnaise (23 mcg).
Should you take a vitamin K supplement? Scientists don't have enough data at this point to recommend a dietary supplement of this nutrient for healthy adults.
If You Take Warfarin
Warfarin (Coumadin and Jantoven) is a widely used blood-thinning medication given to people who have had or are likely to develop an artery-blocking blood clot. Warfarin is of ten prescribed following a heart attack, stroke, blood clot in the leg (deep vein thrombosis) or a clot that has traveled to the lung (pulmonary embolism). The drug is also used in people who have an irregular heart rhythm (atrial fibrillation) or an artificial heart valve.
Warfarin works by decreasing the activity of vitamin K.
If you take warfarin: Don't eat dark, leafy green vegetables. The amount of vitamin K in these foods can vary threefold, depending on where they're grown. For example, a serving of spinach could contain 200 mcg of vitamin K...or 600 mcg. That's a significant difference in vitamin K intake for someone taking warfarin, who should not have large fluctuations in intake of this vitamin.
Instead, eat three daily servings of vitamin K-rich foods with lower but predictable amounts of the nutrient. That could include one-half cup of broccoli, one-half cup of green peas or six ounces of tomato juice. Other good choices of foods that contain relatively low amounts of vitamin K include asparagus and green beans.
To help determine the dose of warfarin that prevents blood clots from forming, doctors test the coagulation time-a measurement known as the International Normalized Ratio and Prothrombin Time (INR/PT). INR/PT is checked monthly, and the patient is instructed to maintain a consistent dietary intake of vitamin K to avoid altering the effectiveness of warfarin.
