What is vitamin K?
Vitamin K is a fat-soluble vitamin that comes in two forms. Vitamin K1, or phylloquinone, comes from plants. It is the main type of dietary vitamin K. A lesser source is vitamin K2, or menaquinone, which occurs in some animal-based and fermented foods.
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.
Vitamin K helps to make various proteins that are needed for blood clotting, the building of bones and regulating blood calcium levels. 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.
When people eat foods containing K1, bacteria in the large intestine convert it to its storage form, vitamin K2. It is absorbed in the small intestine and stored in fatty tissue and the liver.
Without vitamin K, the body cannot produce prothrombin.
Types of vitamin K
Several forms of vitamin K are used in dietary supplements, including vitamin K1 and vitamin K2. The limited data available suggests that K2 is the best form for higher absorption.
Health benefits of vitamin K
Vitamin K benefits the body in various ways.
1. Bone health
There appears to be a link between low intake of vitamin K and osteoporosis. Many studies have suggested that vitamin K supports the maintenance of strong bones, improves bone density and decreases the risk of fractures.
2. Cognitive health
Increased blood levels of vitamin K have been linked with improved episodic memory in older adults.
3. Heart health
Vitamin K may help keep blood pressure lower by preventing mineralisation, where minerals build up in the arteries. This enables the heart to pump blood freely through the body.
Signs & symptoms of vitamin K deficiency:
Deficiency is rare, but, in severe cases, it can increase clotting time, leading to haemorrhage and excessive bleeding. The following are common signs of a deficiency:
- A longer time for blood to clot
- Osteopenia or osteoporosis
Sources of vitamin K
- Green leafy vegetables including collard greens, kale, spinach, broccoli, Brussels sprouts, cabbage, lettuces
- Soybean and canola oil
- Prunes, kiwi fruit
- Salad dressings made with soybean or canola oil
- Fortified foods
- Fermented soybeans
- Smaller amounts in meat, liver, cheese, eggs
Vitamin K is present in most multivitamin/multimineral supplements, typically at values less than 75% of the recommended dietary intake. It is also available in dietary supplements containing only vitamin K or vitamin K combined with a few other nutrients, frequently calcium, magnesium, and/or vitamin D. These supplements tend to have a wider range of vitamin K doses than multivitamin/mineral supplements.
Caution before supplementing
Vitamin K can interact with several common medications, including blood-thinners, anticonvulsants, antibiotics, cholesterol-lowering drugs, and weight-loss drugs. People who use blood-thinning medications, such as warfarin should not start consuming additional vitamin K without first asking a doctor.
Vitamin K is a fat-soluble vitamin with two forms. Its main role in the body is to support bone, brain and heart health. If you plan to supplement with vitamin K, proceed with caution as it can interfere with several medications. Always talk to your health practitioner if you’re considering supplementing with vitamin K.
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