Vitamin K is a fat-soluble vitamin that plays an important role in blood clotting. This role in blood clotting is vitamin K’s most well known property. But it does much more than that.
This newsletter will look at the properties and functions of vitamin K, and its food sources, as well as the various health conditions that require vitamin K for their prevention and/or treatment.
A new vitamin was discovered in 1929 and was called ‘the coagulation vitamin’. The initial discoveries were reported in a German journal, in which it was designated as Koagulationsvitamin and thus received the letter K.
Vitamin K is actually a group of lipophilic and hydrophobic vitamins needed to modify certain proteins, mostly required for blood coagulation, and also a number of other proteins that chelate calcium ions and are involved in bone and other tissue metabolism. Thus it is not a single chemical substance, but rather a family of chemically related substances, that go by the general name of “vitamin K”.
All types of vitamin K are part of a large chemical category of substances called naphthoquinones. They all share a methylated naphthoquinone ring structure. Within this category there are two basic types of vitamin K. The first type (referred to as vitamin K1), called phylloquinones, is made by plants. The second basic type (referred to as vitamin K2), called menaquinones, is made by bacteria. We get most of our dietary vitamin K (up to 90%) in the form of phylloquinones from plant foods. Many different types of bacteria in the gastrointestinal tract can make vitamin K in the form of menaquinones and this contributes to our vitamin K requirements, although this contribution is mush less than previously thought. Vitamin K3 is a synthetic form of vitamin K.
It is generally accepted that the naphthoquinone is the functional part of the vitamins K, so that the mechanism of action is similar for all K-vitamins.
Physiology and Action
The function of vitamin K in the cell is to convert glutamate in proteins to form gamma-carboxyglutamate residues, by the process of carboxylation. These are called Gla-residues. Gla-residues are usually involved in binding calcium. The Gla-residues are essential for the biological activity of all known Gla-proteins.
There are some 14 human proteins with Gla-residues and they play key roles in the regulation of three physiological processes:
· Blood coagulation
· Bone metabolism
· Vascular biology.
Like other fat-soluble vitamins (A, D, E), vitamin K is stored in the fat tissue of the human body.
Food Sources of Vitamin K1 and K2
Excellent sources of vitamin K1 include:
· Leafy green vegetables such as spinach, Swiss chard
· The Brassica family e.g. cabbage, kale, cauliflower, broccoli and Brussels sprouts
· Green beans, asparagus and mustard greens
· Avocado and kiwifruit.
Very good sources of vitamin K1 include:
· Green peas, carrots
· Cereal grains.
The best natural source of vitamin K2 is derived from the ancient Japanese food called Natto. Natto is made from fermented soybeans where the bacteria Bacillus natto is part of the fermentation process which converts K1 into K2. Vitamin K2 is also present in other fermented foods such as certain types of cheese, especially cheese curd.
Many bacteria, such as Escherichia coli found in the large intestine, can synthesise vitamin K2 (but not vitamin K1).
Deficiency of Vitamin K
Average diets are usually not lacking in Vitamin K, and primary vitamin K deficiency is rare in healthy adults.
Newborn infants, especially premature babies, are at an increased risk of deficiency. It is generally recommended that 0.5-1.0 mg vitamin K1 be administered to all newborns shortly after birth.
There is an increased prevalence of vitamin K deficiency in individuals with liver disease, cystic fibrosis and inflammatory bowel disease, and in individuals after recent abdominal surgery.
Secondary vitamin K deficiency can occur in those with bulimia or those on stringent diets and in those taking anticoagulants.
Symptoms of Vitamin K Deficiency
· Blood Clotting
Persons deficient in vitamin K are first and foremost likely to have symptoms related to problematic blood clotting or bleeding. These symptoms can include heavy menstrual bleeding, gum bleeding, bleeding within the digestive tract, nose bleeding, easy bruising, blood in the urine and anaemia.
· Bone Problems
A second set of vitamin K deficiency-related symptoms involves bone problems. These include loss of bone (osteopenia), decrease in bone mineral density (osteoporosis) and fractures, including common age-related fractures like that of the hips.
· Calcium Deposition
Another set of vitamin K deficiency-related symptoms involves excess deposition of calcium in soft tissues. These include hardening of the arteries or calcium-related problems with heart valve function.
Functions of Vitamin K
· Promotes Healthy Blood Clotting
In terms of health research, vitamin K is best known for its role in healthy blood clotting.
Blood clotting is a body process that is critical for our everyday health. At one end of the spectrum, whenever we get a skin wound (even a simple cut) we need sufficient blood clotting ability to close the wound and prevent excessive bleeding. At the other end of the spectrum, we do not want too much blood clotting ability so that, when we are not wounded, there will be no clots forming in our cardiovascular system and mistakenly block an otherwise functioning blood vessel. Vitamin K is one of the key nutrients for keeping our blood clotting ability at the exact right level. Vitamin K is involved in helping the clotting factors (including clotting factors II, VII, IX, and X) achieve their proper stickiness.
The anticoagulant drug Warfarin works by interrupting this process. For individuals with an excessive tendency to form blood clots, anticoagulants like Warfarin can be lifesaving.
· Protects Bones from Weakening or Fracture
Vitamin K is a critical nutrient for bone health. Individuals who are vitamin K deficient have been clearly shown to have a greater risk of fracture. These bone-related benefits of vitamin K appear to depend on at least two basic mechanisms.
The first mechanism involves a type of bone cell called osteoclasts. These cells bring about bone demineralisation - they help take minerals out of the bone and make them available for other body functions. (Osteoblast bone cells do the opposite). Excessive activity of osteoclasts would lead to too much demineralisation. Vitamin K makes it possible for our body to keep this process in check. It blocks the formation of too many osteoclasts and perhaps also initiates their programmed cell death (a process called apoptosis).
A second mechanism involves the role of vitamin K in a process called carboxylation (the same process involved in the stickiness of clotting factors required for proper blood clotting). For our bones to be optimally healthy, one of the proteins found in bone, osteocalcin, needs to be chemically altered through the process of carboxylation. When too few of the osteocalcin proteins in our bones are carboxylated, our bones have an increased risk for fracture. Since vitamin K is required for proper activity of carboxylase, the enzyme that allows carboxylation of the osteocalcin proteins in our bones, vitamin K can restore these bone proteins to their proper place in our bone structure and strengthen the composition of the bone.
· Prevents Calcification of Blood Vessels or Heart Valves
One common problem in many forms of heart disease is unwanted calcification, the build-up of calcium inside a tissue that is normally soft. This build-up of calcium causes the tissue to harden and stop functioning properly, as happens in hardening of the arteries or of the heart valves. To inhibit the build-up of calcium in the arteries it is necessary to maintain adequate supplies of a special protein, matrix Gla protein (MGP). MGP directly blocks the formation of calcium crystals inside the blood vessels. For MGP to function in this way, it must first be present in its carboxyled form. Vitamin K is required for this carboxylation process.
Researchers have determined that individuals with vitamin K deficiency are at greater risk of hardening of the arteries than individuals with healthy vitamin intake.
· Other Roles for Vitamin K
Researchers continue to explore a wide range of health-supportive roles for vitamin K in three areas:
i) Protection against oxidative damage
ii) Proper regulation of inflammatory response
iii) Support of brain and nervous tissue structure.
This may have applications in the areas of diabetes, Alzheimer’s disease and cancer.
The U.S. Dietary Reference Intake and the National Academy of Sciences recommend:
· 120 micrograms/day for adult males
· 90 micrograms/day for adult females
· 10-20 micrograms/day for infants
· 15-100 micrograms/day for children and adolescents.
Although allergic reaction from supplements is possible, there is no known toxicity associated with high doses of the phylloquinone (vitamin K1) or menaquinone (vitamin K2) forms of vitamin K. However the synthetic form of Vitamin K, Vitamin K3, menadione, is demonstrably toxic (allergic reactions, haemolytic anaemia and cytotoxicity in liver cells).
Phylloquinone (vitamin K1) and menaquinone (vitamin K2) are capable of blocking the blood thinning action of anticoagulants like the drug Warfarin which work by interfering with the action of vitamin K.
Some cholesterol-lowering drugs that work by interfering with bile acids can reduce the absorption of vitamin K
Antibiotics, especially the broad-spectrum ones, can decrease the availability of vitamin K by killing gut bacteria that synthesise vitamin K.
High doses of calculates, including foods with a high salicylate content such as nuts, spices and mints, and drugs such as acetylsalicylic acid (Aspirin) and aluminium hydroxide antacids may also decrease the availability of vitamin K.
Due to the high number of dietary sources, a nutritious and balanced diet will ensure a healthy intake of vitamin K and, because of this, deficiency of this vitamin is rare except under the various states as outlined above.
However, although the majority of people get enough vitamin K to maintain adequate blood clotting, it is suggested by many experts in this field that most of us do not get enough to give the other benefits of vitamin K as set out above.
Increase the intake of the vitamin K-rich foods to enhance your health.
*Copyright 2011: The Huntly Centre.
Disclaimer: All material in the huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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