Best food groups: Green leafy vegetables
Also consider: Brussels sprouts, parsley, broccoli, asparagus
What is vitamin K and why is it so important? Without it, our body would be one big bruise! Vitamin K is integral to what is called the blood-clotting cascade (coagulation) which prevents constant bleeding when we cut ourselves and internal hemorrhaging. Vitamin K is also extremely important in bone formation and in the prevention of osteoporosis. People who are on blood-thinning medications, such as Coumadin (warfarin), are often advised to limit their intake of foods rich in vitamin K. But research shows that having regular intake of vitamin K helps the body exert better control of the anticoagulation effect of the medicine and balance it with clotting needed in the body. The key is having a consistent intake of vitamin K–rich foods, which helps the doctor better regulate the anticoagulant medication.
Did you know? Vitamin K actually refers to a group of fat-soluble vitamins: K1, also known as phylloquinone, comes from plant sources; and K2, which refers to a subgroup called menaquinones, comes from animal sources and the synthesis of intestinal bacteria.
The K in vitamin K came from a German medical journal, where it was referred to as Koagulationsvitamin.
How much is enough?
The DV for vitamin K is 80 mcg, based on a 2,000-calorie diet.
An UL for vitamin K hasn't been established. Consuming high amounts of vitamin K via food sources generally doesn't pose a problem. However, high intake of vitamin K supplements has been known to cause liver damage and jaundice. Again, if you are prescribed blood thinners, be sure to discuss your dietary intake of this vitamin with your doctor.
Supplements: Vitamin K can be found in multivitamins or as a supplement alone. Supplementing vitamin K has been showed to increase bone density and reduce bone loss and fractures.
1. Kale
For the skinny on kale, see page 288. Kale belongs to the cruciferous vegetable family, a category of vegetables linked to cancer prevention. High intake of cruciferous vegetables, such as kale, has been related to reduced risk of both breast and prostate cancer.
2. Collard Greens
For best cholesterol-lowering benefits, make sure to cook your collards. A study found that cooked versus raw collards did a much better job on binding cholesterol contained in the digestive system.
3. Spinach
There are different varieties of spinach, ranging from flat leaves, smooth leaves, to savory, crinkled leaves. Baby spinach is usually flat-leafed. Spinach was shown to help improve blood flow and lower blood pressure in a randomized control study. The flavonoids and nitrates in spinach help produce nitric acid, which helps open up blood vessels.
4. Turnip Greens
Turnip greens are the green leafy portion of the turnip, a root vegetable in the mustard family that was originally brought to the United States by colonists. Turnip greens contain glucoraphanin, a plant chemical that produces sulforaphane, a potent anticancer substance.
Did you know?
Onions may not be what first comes to mind when you think of a "leafy green," but they do provide over twice the RDA for vitamin K per cup serving. They also contain the flavonoid quercetin and other phytochemicals, which have been shown to protect against cancer, lower high blood pressure, and reduce the risk of heart attack.
5. Beet Greens
Beet greens are very similar to turnip greens in that they are the sprout that comes up from the top of the root. They are an excellent source of vitamins A, C, and K, and a good source of riboflavin. An animal study found that mice that were fed a high-fat, high-cholesterol diet could prevent lipid peroxidation and improve antioxidant status when their diet was supplemented with beet greens.
6. Dandelion Greens
Dandelion greens are an excellent source of vitamins A, C, and K, and a good source of calcium. Dandelion flowers are commonly used to make wine. Dandelions have traditionally been used in different medical systems from around the world, including Native American and Arabic medicine. Extracts of dandelion have been shown to have antiviral and anti-influenza properties.
The word dandelion originates from the French phrase dent de lion, "lion's tooth," inspired by the jagged appearance of the plant's leaves.
7. Swiss Chard
Swiss chard is a member of the beet family, with the difference that the bulb it produces is not edible. Swiss chard is packed with 961 mg, or 27 percent, of the DV of potassium, which helps regulate blood pressure. It is also rich in iron, magnesium, and vitamins A, C, and K, and a good source of calcium and fiber. However, you might wish to watch your intake if watching your sodium; Swiss chard boasts one of the highest-occurring levels of sodium of all vegetables, with 313 mg per cup cooked.
Scientists in Urbino, Italy, discovered a flavonoid substance called xylosylvitexin in Swiss chard leaves and seeds, which inhibits the growth and duplication of human colon cancer cells. Another interesting fact is that it's not really "Swiss" at all, but originated in Sicily—a Swiss botanist named it after his beloved Switzerland.
Source: USDA National Nutrient Database for Standard Reference, Release 24