Vitamin K is necessary for blood clotting. It is both produced in the body by intestinal bacteria and provided by food. Discover the role of this vitamin, its recommended nutritional intake, the risks of deficiency or overdosage, and its medical applications. Vitamin K is one of the fat-soluble vitamins.
It exists in several forms in the diet:
Phylloquinone or vitamin K1: found in plants: green vegetables (especially darker ones such as spinach, broccoli, and asparagus), seaweed, and, to a lesser degree, soybean (9 µg per tablespoon) and canola (6 µg per tablespoon) oils. For example, a cup of cooked broccoli (200 g) provides 220 µg of vitamin K1 and a cup of cooked spinach (200 g) provides 888 µg2. Cooking does not destroy vitamin K.
Menaquinones or K2 vitamins: provided by foods of animal origin: vitamin K2 is found in miso (fermented soybean paste), liver, milk, cheese, yogurt, and fish oils.
Roles in the body
Vitamin K has long been known for its role in blood clotting: it activates several clotting factors and thus prevents bleeding.
Researchers have recently discovered that it is essential for bone health, facilitating the action of osteocalcin, a protein secreted by osteoblasts (young bone marrow cells that form the framework of bone tissue), whose dosage in the blood can reveal a disorder in the formation of bone tissue. Vitamin K is said to be essential for bone growth in children and adolescents as well as for the prevention of osteoporosis in adults.
Nutritional reference (recommended dietary intake)
| Nutritional reference in vitamin K in microgames (µg) per day |
| |
| |
Children from 10 à 12 Ans | |
Adolescents de 13 à 15 Ans | |
Adolescents de 16 à 19 Ans | |
| Adults | |
Pregnant or breastfeeding women | |
| |
The recommended nutritional intakes could be revised upwards. Indeed, the recommendations are currently based on the quantities necessary to obtain an optimal synthesis of coagulation factors. Recent evidence of vitamin K requirements for the production of other proteins such as osteocalcin has prompted some researchers to propose higher recommended intakes.
In addition, most health agencies recommend an intake of 1 µg per kilogram of body weight per day. Thus, the European Food Safety Authority (EFSA) has set a nutritional reference value (average for an adult) of 75 µg per day2.
Indications
- Prevent and treat osteoporosis.
- Prevent cardiovascular disorders.
Note. In conventional medicine, high doses of vitamin K are used to counteract the harmful effects of an overdose of warfarin (an anticoagulant) or blood clotting failure.
Osteoporosis Most epidemiological studies indicate that vitamin K deficiency is associated with reduced bone density5-7 and an increased risk of fractures8-10 in people over 60 years of age and postmenopausal women.
In 2003 and 2004, two studies of postmenopausal women showed that supplements of vitamin D and calcium increased bone density11 or slowed its decline12 more markedly when combined with vitamin K1. These results were contradicted in 2008 by other researchers, who noted an improvement in the indices of bone demineralization.
A large study published in 2008 found that vitamin K1 did not prevent age-related decline in bone density. However, it would significantly reduce the possibility of fractures in women with osteopenia.
With respect to vitamin K2, studies and meta-analyses show that a high dose of this vitamin (45 mg per day), taken alone or with vitamin D3 or calcium, can increase or preserve bone density in postmenopausal women. It also reduces the risk of fracture in people who are vitamin K deficient or have osteoporosis.
Most studies have been conducted in Japan. Japanese women generally have lower bone density than their Western counterparts, but paradoxically, they have fewer hip fractures. The reasons, which could be socio-cultural, anatomical, genetic, are not known at this time. Still, several researchers believe that the effects of vitamin K are not entirely extrapolated to Western women. For example, a study in Denmark found no relationship between vitamin K intake and bone density or incidence of fractures. Although the results require confirmation by trials in Western women, all authors agree that high dietary vitamin K intake is important for maintaining bone health.
Moreover, among the trials conducted in Japan, 4 involved a total of 120 subjects taking prednisolone (a corticosteroid): vitamin K2 (45 mg per day), taken alone or with vitamin D, proved useful in reducing bone demineralization caused by this drug.
Cardiovascular Protection: Vitamin K may play a protective role against atherosclerosis and cardiovascular disease. Indeed, a link has been established between vitamin K deficiency and an increased risk of arterial calcification. Researchers have also shown that taking vitamin K1 supplements slows the progression of this calcification or reduces the loss of elasticity of the arteries36. Finally, women with postmenopausal osteoporosis are at greater risk of developing atherosclerosis.
Precautions
Attention
It is generally recommended for people taking warfarin. This medication is usually prescribed for :
- Prevention of thromboembolic events in embolic heart disease
- Prevention of thromboembolic events following myocardial infarction.
- Prevention of thromboembolic events when wearing a valve prosthesis
Indications-
Heart disease
Emboligens: prevention of related thromboembolic complications
with certain atrial rhythm disorders (atrial fibrillations, flutter, atrial tachycardia), certain mitral valvulopathies, valve prostheses.
Prevention
Thromboembolic complications of myocardial infarction
Complicated: wall thrombus, severe left ventricular dysfunction, embolismic dyskinesia..., in the relay of heparin.
Treatment
Deep vein thrombosis and pulmonary embolism and the prevention of their recurrence, in the relay of heparin.
Avoid changing their vitamin K intake (food or supplements) in a pronounced way, in order to ensure the stability of the effect of this anticoagulant medication.
The absorption of vitamin K can be impaired by alcoholism and the use of mineral oil (kerosene oil or petroleum jelly).
Contraindication
Hypersensitivity to vitamin K
Undesirable effect
Even at very high doses taken for one or two years, vitamin K did not cause any significant adverse effects.
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