Vitamin K has important functions within the body, some of which are still being discovered. Research has shown that vitamin K is an anticalcification, anticancer, bone-forming and insulin-sensitising molecule. Recent data indicate that subclinical vitamin K deficiency is not uncommon. Additionally, vitamin K antagonists such as warfarin may cause detrimental side effects, which may partly be blunted through vitamin K supplementation.
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, menaquinones, are found in some animal foods and fermented foods. Menaquinones can also be produced by bacteria in the human body.
Vitamin K helps to make various proteins that are needed for blood clotting and the building of bones. Prothrombin is a vitamin K-dependent protein directly involved with blood clotting. Osteocalcin is another protein that requires vitamin K to produce healthy bone tissue.
Vitamin K is found throughout the body including the liver, brain, heart, pancreas, and bone. It is broken down very quickly and excreted in urine or stool. Because of this, it rarely reaches toxic levels in the body even with high intakes, as may sometimes occur with other fat-soluble vitamins.
Recommended Amounts
AI: An “adequate intake” (AI) is used when there is not enough evidence to establish a Recommended Dietary Allowance (RDA). The AI amount is estimated to ensure nutritional adequacy. For adults 19 years and older, the AI for vitamin K is 120 micrograms (mcg) daily for men and 90 mcg for women and for those who are pregnant or lactating.
Sources
Bacteria in the gastrointestinal tract naturally make vitamin K. Dietary sources of vitamin K include green leafy vegetables — collards, green leaf lettuce, kale, mustard greens, parsley, romaine lettuce, spinach, Swiss chard and turnip greens — as well as vegetables such as broccoli, Brussels sprouts, cauliflower and cabbage, according to the U.S. National Library of Medicine (NLM). Other sources that are less rich in vitamin K include meats, fish, liver, eggs and cereals.
Benefits
Vitamin K is an important factor in bone health and wound healing. Vitamin K is a fat-soluble vitamin that makes proteins for healthy bones and normal blood clotting. According to the Harvard School of Public Health, vitamin K helps produce four of the 13 proteins needed for blood clotting.
K also teams up with other vitamins. “Vitamin K works with vitamin D to ensure that calcium finds its way to the bones to help them develop properly,” Dr. Sherry Ross, women’s health expert at Providence Saint John’s Health Center in Santa Monica, California, said.
Signs of Deficiency
Vitamin K deficiency in adults is rare, but may occur in people taking medications that block vitamin K metabolism such as antibiotics, or in those with conditions that cause malabsorption of food and nutrients. A deficiency is also possible in newborn infants because vitamin K does not cross the placenta, and breast milk contains a low amount. The limited amount of blood clotting proteins at birth increases the risk of bleeding in infants if they are not given vitamin K supplements. 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 vitamin K 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 vitamin K 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!
Source:
- National Institutes of Health Office of Dietary Supplements: Vitamin K Fact Sheet for Health Professionals https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/. Accessed 6/25/2018.
- Weber P. Vitamin K and bone health. Nutrition. 2001;17:880–7.
- Feskanich D, Weber P, Willett WC, Rockett H, Booth SL, Colditz GA. Vitamin K intake and hip fractures in women: a prospective study. Am J Clin Nutr. 1999;69:74–9.
- Booth SL, Tucker KL, Chen H, et al. Dietary vitamin K intakes are associated with hip fracture but not with bone mineral density in elderly men and women. Am J Clin Nutr. 2000;71:1201–8.
- Booth SL, Broe KE, Gagnon DR, et al. Vitamin K intake and bone mineral density in women and men. Am J Clin Nutr. 2003;77:512–6.
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