Vitamin K

Vitamin K is a fat-soluble vitamin that comes in two forms. The main type is called phylloquinone, found in green leafy vegetables like collard greens, kale, and spinach. The other type is menaquinones.

Recommended Amounts 

For adults 19 years and older, the AI is 120 micrograms (mcg) daily for men and 90 mcg for women and for those who are pregnant or lactating.

Vitamin K and Health

Bone health

It is involved with the production of proteins in bone, including osteocalcin, which is needed to prevent the weakening of bones. In addition, low blood levels of vitamin K have been linked with low bone density.  A report from the Nurses’ Health Study suggests that women who get at least 110 mcg of it a day are 30% less likely to break a hip than women who get less than that.      Among the nurses, eating a serving of lettuce or other green, leafy vegetable a day cut the risk of hip fracture in half when compared with eating one serving a week. Data from the Framingham Heart Study also showed an association between its high intake and reduced risk of hip fracture in men and women and increased bone mineral density in women. However, the results of clinical trials and meta-analyses have been conflicting whether its supplements reduce bone fractures.   This may be due to a variety of other factors that affect bone health, including a lack of calcium, vitamin D, and weight-bearing exercise, all of which might mask a benefit of vitamin K supplementation.

Vitamin K Food Sources

• Phylloquinone
  • Green leafy vegetables including collard and turnip greens, kale, spinach, broccoli, Brussels sprouts, cabbage, lettuces
  • Soybean and canola oil
  • Salad dressings made with soybean or canola oil
  • Fortified meal replacement shakes
• Menaquinones
  • Natto (fermented soybeans)
  • Smaller amounts in meat, cheese, eggs

Vitamin K Signs of Deficiency

Its deficiency in adults is rare. The following are the most common signs of a deficiency.

• A longer time for blood to clot or a prolonged prothrombin time (as measured in a physician’s office)
• Bleeding
• Hemorrhaging
• Osteopenia or osteoporosis

Did You Know?

• Antibiotic medicines may destroy vitamin-K-producing bacteria in the gut, thereby potentially decreasing its levels especially if taking the medicine for more than a few weeks.  People who have a poor appetite while using long-term antibiotics may be at greater risk for a deficiency, and may benefit from a vitamin K supplement.
• Because it is fat-soluble, it is best to eat vitamin K foods with some fat to improve absorption. So, drizzle some olive oil or add diced avocado to your favorite leafy green salad!