Vitamin K is a fat soluble vitamin, primarily involved in helping the blood clot, and production of blood clotting factors. Vitamin K also helps to maintain bone health by helping to produce proteins necessary for the normal calcification of bone.
Forms of vitamin K
There are two forms of vitamin K – K1 and K2. K1 is also known as phylloquinone and phytomenadione. Green leafy vegetable are good sources of Vitamin K1. Vitamin K2 (menaquinones) is converted by bacteria found in your normal flora in the intestines and vitamin K3 (menadione) is available as a synthetic form.
How much vitamin K do I need?
Most people can get a sufficient amount of vitamin K simply by eating a balanced diet. Any excess vitamin K not required by your body is stored in the liver for future use.
Vitamin K needs are based on each kilogram of body weight and is approximately 0.001mg per kg. This means if someone weighs 70kg they would need 0.070mg a day of vitamin K.
Vitamin K deficiency in adults is rare but common in newborn infants. A single dose of vitamin K is usually given to all newborns to help with preventing vitamin K deficiency bleeding.
While vitamin K deficiencies are uncommon in most adults in the UK, you may be at higher risk if you are severely malnourished, take medication that may interfere with vitamin K absorption, have a disease which affects the absorption in the digestive tract such as ulcerative colitis or Crohn's disease. Typical signs and symptoms of vitamin K deficiency can manifest as excessive bleeding, bruising easily, and blood in the urine or stools.
Can I take too much vitamin K?
There is a lack of available evidence to know what the effects may be of taking high doses of vitamin K supplements each day. However, if you are concerned about vitamin K deficiency a healthcare professional will be able to advise.
Sources of vitamin K
Vitamin K is most commonly found in green leafy vegetables such as broccoli and spinach. In addition, collards boast 1059 μg of vitamin K per cup and are bursting with vitamin A and beta carotene. Other sources of vitamin K include vegetable oils and cereal grains, and smaller amounts can be found in meat and dairy foods.
People with clotting disorders, using warfarin for heart problems, or other conditions may need to change their diets to control the amount of vitamin K they take in. Vitamin K supplements are available orally and in injectable form. A prescription is required for all injectable forms of vitamin K.
Interactions with vitamin K
Many drugs can interfere with the effects of vitamin K such as antacids and blood thinners like warfarin. In fact, vitamin K is given to counteract excessive amounts of warfarin.