Consider blood. It has the remarkable ability to remain liquid even though it’s loaded with all sorts of solid stuff—red and white blood cells, protein, vitamins, minerals, even gobs of fat from the last cheeseburger you ate. But blood can also become solid within seconds when a blood vessel breaks. That particular ability can spell the difference between life and death if you’re seriously injured—and it requires vitamin K. The vitamin got its name from the Danish researchers who discovered it. The "K" stands for "koagulation," the Danish version of "coagulation."
Your body needs it to make several blood proteins involved in clotting, including the most important, prothrombin. When bleeding starts, these proteins go through a quick series of changes that ends with a blood clot, says John Suttie, Ph.D., professor of biochemistry at the University of Wisconsin in Madison. If your body ran short of vitamin K, your blood would clot very slowly, and you might develop many symptoms that are a giveaway—easy bruising, frequent nosebleeds, or cuts that won’t quit bleeding.
Potential Bone Builder
You need vitamin K to make two proteins found in bone. Without it, the bones produce an abnormal form of these proteins that can’t bind to the minerals that normally form bone.
One Japanese study suggests that low vitamin K levels play a role in the breakdown of bone after menopause. Some researchers contend that postmenopausal women are at risk for a low-level vitamin K deficiency that the traditional blood-clotting test would not detect. "However," Dr. Suttie says, "much more needs to be learned about vitamin K’s function in bone before we know for sure whether it plays a role in diseases such as osteoporosis."
Eat the Garnish
Most people get enough of this vitamin from their diets. The average intake is 80 micrograms or so a day, which is the Daily Value.
Good sources include leafy green vegetables such as parsley, spinach, watercress, turnip greens, kale, and broccoli. Vitamin K is also produced in the intestines by bacteria, but it’s likely that these bugs in our guts don’t produce all that much, Dr. Suttie says.
Vitamin K deficiency is not common, he says. People who are most likely to be deficient probably don’t eat leafy green vegetables, or they have medical problems that interfere with fat absorption.
"People who are in the hospital for one reason or another are also at an increased risk for problems," Dr. Suttie says. That’s because they may not have eaten anything for a while, and a deficiency can occur relatively fast—within a few days. There’s an added risk of vitamin K–related complications for people who are taking anticoagulant (blood-thinning) drugs such as warfarin (Coumadin), which block the action of vitamin K. Other causes of depletion are antibiotics or sulfa drugs that can wipe out bacteria in the intestines, making even this small supply unavailable.
SUPPLEMENTSNAPSHOT
| Vitamin K May help: Bleeding problems associated with vitamin K deficiency. Daily Value: 80 micrograms. Special instructions: For best absorption, take a K-containing multivitamin with a meal that contains some fat. There is no need to take supplements unless prescribed by your doctor. Who’s at risk for deficiency: Newborns; people taking anticoagulants (blood thinners), long-term antibiotic therapy, or sulfa drugs; people who eat no green vegetables; and those who have problems with dietary fat absorption. Good food sources: Broccoli, kale, parsley, spinach, turnip greens, and watercress. Cautions and possible side effects: Don’t assume that easy bruising or bleeding is being caused by a vitamin K deficiency; see a doctor if you have these symptoms. If you are taking the anticoagulant warfarin (Coumadin), do not take vitamin K without medical supervision. |
Do You Need Special K?
Luckily, doctors check blood-clotting time in people who are taking anticoagulants or who appear to have bleeding problems. Any problems that might occur are easily corrected with an injection of vitamin K.
Doctors sometimes tell their patients who are taking anticoagulants not to eat anything that contains vitamin K, but that’s not the best advice, Dr. Suttie says. "They should continue to eat the way they did before they started taking the drug and try to keep their intake pretty much the same from week to week," he says. This helps to stabilize the dose of anti coagulant.
Injections of the vitamin are routinely given to newborn infants, who tend to be low on it because it doesn’t cross the placenta very well. Injections are also sometimes used for people who can’t absorb nutrients well or who are on tube feedings.
Vitamin K is found in some multivitamins and in single supplements. If it’s in a multivitamin, you’ll find it listed on the label.
Large intakes of vitamin E—on the order of 2,200 international units (IU) a day—can reduce the absorption of vitamin K in the intestines, according to Dr. Suttie. "People who eat normal amounts of vitamin K–rich foods, however, can safely take 400 IU of vitamin E every day for long periods of time," he says.
