Vitamin K (Naphthoquinones)

Vitamin K is a group of fat-soluble vitamins also called naphthoquinones. Within the Vitamin K group are vitamins K, K1, K2 and K3. The natural form of Vitamin K is Vitamin K1, or Phylloquinone, which is present in a number of plants and is the main source of Vitamin K obtained through food.

Vitamin K is stored in fat tissue and the liver and plays an essential role in the regulation of blood clotting. It also helps with maintaining healthy bones and reducing bone loss given its part in transporting calcium throughout the body.

Sources of Vitamin K

Vitamin K is found primarily in chlorophyll, the substance in plants that gives them a green color. Food sources of vitamin K include:

• Green tea
• Turnip greens
• Broccoli
• Kale
• Parsley
• Spinach
• Cabbage
• Asparagus
• Dark green lettuce and other leafy greens

Vitamin K2, which is especially helpful in preventing fractures and increasing bone density, is found in:

• Fermented dairy, such as yogurt and cheese
• Fermented soy, including miso and natto
• Beef and chicken liver

Freezing foods may negatively affect the amount of vitamin K, but cooking does not.

Vitamin K Deficiency

Since vitamin K is so readily found in leafy greens and is also made by intestinal bacteria, it’s rare to develop a vitamin K deficiency. However, there are a number of health problems that can cause an individual to be at risk, including:

• Chronic malnutrition
• Serious burns
• Long-term hemodialysis
• Alcohol dependency
• Taking antibiotics
• Liver disease
• Vitamin malabsorption caused by conditions such as gallbladder disease, cystic fibrosis, celiac disease, and Crohn’s disease
• Taking blood thinners

Symptoms and side effects may include:

• Easy bruising
• Gastrointestinal bleeding
• Excessive menstrual bleeding
• Bloody urine
• Issues with blood clotting
• Increased bleeding, starting from the gums or nose

Vitamin K Nutrition Information

In addition to its important role in coagulating blood, vitamin K may also reduce the risk of bone fractures and help prevent hardening of the arteries or other soft tissues given its role in the transportation of calcium.

Medical Uses of Vitamin K

Vitamin K may play a role in the prevention and treatment of some health problems:

Excessive Bleeding: Vitamin K has been used to treat and prevent the risk of bleeding in liver disease, when the body can’t absorb enough vitamin K, or when individuals need to be on antibiotics for an extended period of time.

Osteoporosis: Vitamin K is required for the body to effectively use calcium to build strong, healthy bones. Studies have shown that people with higher levels of vitamin K also have greater bone density, and some individuals with osteoporosis have been found to have low levels of vitamin K. Studies have also suggested an association between low levels of vitamin K and a higher risk of osteoarthritis. Further research is needed.

Recommended Daily Intake

According to the National Institutes of Health (NIH), the U.S. Recommended Daily Allowance (RDA) of vitamin K is as follows:

• Infants:
  • 0 - 6 months — 2.0 mcg per day.
  • 7 - 12 months — 2.5 mcg per day.
• Children:
  • 1 - 3 years — 30 mcg per day.
  • 4 - 8 years — 55 mcg per day.
  • 9 - 13 years — 60 mcg per day.
• Adolescents and adults:
  • 14 - 18 years — 75 mcg per day.
  • 19 and older — 90 mcg per day.

Vitamin K Toxicity

There is no known toxicity of the natural forms of Vitamin K (K1 and K2), but high doses may cause numbness or tingling in the hands and feet.

On the other hand, the synthetic form of Vitamin K, Vitamin K3, is known to be highly toxic and over-the-counter sale of K3 supplements have been banned by the FDA. High doses have caused allergic reactions, hemolytic anemia, and cytotoxicity in liver cells.