Vitamin K is actually a group of compounds. The most important of these compounds appears to be vitamin K1 and vitamin K2. Vitamin K1 is obtained from leafy greens and some other vegetables. Vitamin K2 is a group of compounds largely obtained from meats, cheeses, and eggs, and synthesized by bacteria.
Vitamin K1 is the main form of vitamin K supplement available in the U.S.
Recently, some people have looked to vitamin K2 to treat osteoporosis and steroid-induced bone loss, but the research is conflicting. At this point there is not enough data to recommend using vitamin K2 for osteoporosis.
Why do people take vitamin K?
Low levels of vitamin K can raise the risk of uncontrolled bleeding. While vitamin K deficiencies are rare in adults, they are very common in newborn infants. A single injection of vitamin K for newborns is standard. Vitamin K is also used to counteract an overdose of the blood thinner Coumadin.
While vitamin K deficiencies are uncommon, you may be at higher risk if you:
- Have a disease that affects absorption in the digestive tract, such as Crohn's disease or active celiac disease
- Take drugs that interfere with vitamin K absorption
- Are severely malnourished
- Drink alcohol heavily
In these cases, a health care provider might suggest vitamin K supplements.
Uses of vitamin K for cancer, for the symptoms of morning sickness, for the removal of spider veins, and for other conditions are unproven.
How much vitamin K should you take?
The recommended adequate intake of vitamin K you take in, both from food and other sources is below. Most people get enough vitamin K from their diets.
Children 0-6 months
Children 7-12 months
Women 19 and up
Women, pregnant or breastfeeding (19-50)
Women, pregnant or breastfeeding (under 19)
Men 19 and up
There have been no adverse effects of vitamin K seen with the levels found in food or supplements. However, this does not rule out danger with high dose. Researchers have not set a maximum safe dose.
Can you get vitamin K naturally from foods?
Good natural food sources of vitamin K include:
- Vegetables like spinach, asparagus, and broccoli
- Legumes like soybeans
You can also meet your daily requirement with foods that have lesser amounts of vitamin K:
- Meat like liver
What are the risks of taking vitamin K?
Side effects of oral vitamin K at recommended doses are rare.
Interactions. Many drugs can interfere with the effects of vitamin K. They include antacids, blood thinners, antibiotics, aspirin, and drugs for cancer, seizures, high cholesterol, and other conditions.
Risks. You should not use vitamin K supplements unless your health care provider tells you to. People using Coumadin for heart problems, clotting disorders, or other conditions may need to watch their diets closely to control the amount of vitamin K they take in. They should not use vitamin K supplements unless advised to do so by their health care provider.