The term vitamin K indicates a group of fat-soluble compounds (which dissolve well in fats) similar to each other, but not overlapping for structure and molecular properties or for level of activity in the body, variously distributed in nature.
Vitamin K1, also called phylloquinone (and not “phyloquinone”, as sometimes happens to read), is the main food source of vitamin K for the Western population and is present in abundance in all dark green leafy vegetables (such as spinach, radicchio, lettuce and other types of salad, etc.) and in vegetables belonging to the large Brassicaceae family , i.e. broccoli, cauliflower, cabbage, cabbage, Brussels sprouts, turnip greens, radishes, turnips, arugula, horseradish, etc. Chickpeas, peas, soy and green tea also contain vitamin K.
Vitamin K2, a term under which different versions of a substance called menaquinone (MK) are grouped, is mainly present in foods of animal origin, such as meat, beef and pork liver, cheese and eggs.
Milk, on the other hand, contains very small amounts of menaquinones, which is why infants who are exclusively breastfed to avoid vitamin K deficiency are usually supplemented in the first 3 months (unlike babies fed with milk formulas, usually enriched with this vitamin).
The different menaquinones (MK) are indicated by a number, from 4 to 13, corresponding to the length of the side chain of the molecule (number of unsaturated isoprene residues), on which the level of activity and some details of the metabolism of the individual compounds of this group depends.
Except for MK-4, menaquinones are also produced by the intestinal bacterial flora capable of fermenting foods introduced with the diet. Some believe that, except in the case of infants, by virtue of this constant supply by anaerobic bacteria present in the colon it is difficult for the human body to develop vitamin K deficiencies after the first years of life, even if foods that are rich in it are not regularly taken. However, there are no reliable data on the amount of menaquinones produced by the microflora actually absorbed by the intestinal mucosa and, therefore, on the contribution offered by this source to the satisfaction of daily needs.
Vitamin K activity
The main activity of vitamin K is summarized in the letter that identifies it, the initial of the word “koagulation”, or coagulation in German, and was discovered in 1935 by the scientist Henrik Carl Peter Dam, observing the ability of some compounds to reverse bleeding diseases in animals fed with cereals and yeasts.
Further research conducted in the following years has clarified that the compounds collectively referred to as vitamin K are essential for the functioning of some coagulation factors, in particular prothrombin and factors VII, IX and X, necessary to prevent bleeding from occurring in case of even very mild trauma or even spontaneously.
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In addition to antihemorrhagic activity, vitamin K performs countless functions in the body through the regulation of enzymes involved in several fundamental processes.
In addition to coagulation factors and some enzymes with anticoagulant activity (proteins C, S and Z), among the main vitamin K-dependent proteins there are important enzymes involved in the mineralization of bones and soft tissues such as articular cartilage and artery walls.
Vitamin K is, therefore, critical, together with calcium and vitamin D, also in the modulation of bone metabolism, in the prevention of osteoporosis and related fractures.
Transformations in the organism
All forms of vitamin K, namely phylloquinone and various menaquinones, are absorbed in the intestine together with other fat-soluble compounds and in the presence of dietary fats. This means that, to absorb appreciable amounts of phylloquinone present in foods of vegetable origin, it is necessary to add a fatty seasoning (eg extra virgin olive oil or seeds, butter, etc.) or combine cheese or eggs with vegetables.
Moreover, considering that the presence of bile acids and pancreatic enzymes is essential for the absorption process, to obtain vitamin K through the diet it is crucial not to suffer from liver or biliary disorders and to present a good function of the pancreas. Even in optimal gastrointestinal health situations, however, the level of absorption of phylloquinone and menaquinone appears very variable and also linked to the overall composition of the food consumed (in addition to the aforementioned association with a fatty ingredient).
Once absorbed, vitamin K is transferred into the blood after being largely inserted into vesicles called chylomicrons and, in this form, is transported to the liver, the main storage organ.
From the liver, vitamin K is released back into the blood, mostly bound to lipoproteins, when tissues containing vitamin K-dependent proteins, such as bone, require it to perform their functions. Appreciable amounts of vitamin K are also present in the heart, brain and pancreas.
Studies in pregnant women have indicated that vitamin K (in particular, in the form of phylloquinone) is present in the placenta and that the levels of this vitamin in the blood of the fetus are about half of those of the mother, in turn dependent on plant foods (or supplements) taken by the latter with the diet.
Based on the limited data available, it is estimated that the overall average vitamin K content of the human organism (under normal intake conditions and in the absence of symptoms of deficiency) is about 1.5 μg per kg of body weight.
After use, vitamin K and its degradation products are eliminated through the faeces (about 40-50% of the total ingested) together with bile salts or expelled by the kidney, with urine (about 20-30% of the total ingested).
As already mentioned, however, the amount of phylloquinone secreted in breast milk is minimal in women who do not take targeted supplements of this compound during pregnancy and / or after childbirth.
Daily requirement of vitamin K
Let’s see in detail, what are the values for the daily adequate intake (AI) of vitamin K, according to the LARN (Reference intake levels for the Italian population). The values do not vary between the two sexes.
Infants | 6-12 months | 10 μg |
Children-adolescents | 1-3 years | 50 μg |
4-6 years | 65 μg | |
7-10 years | 90 μg | |
11-14 years | 130 μg | |
15-17 years | 140 μg | |
Adults | 18-59 years | 140 μg |
> 60 years | 170 μg |
Deficiency
For a person in good health, without absorption deficits or significant alterations of the intestinal microflora and with a varied diet, vitamin K deficiency is very unlikely, considering that phylloquinone is widely present in food and bacteria present in the colon produce menaquinones in abundance.
On the other hand, people who have to take drugs that interfere with the action of intestinal bacteria (antibiotics, sulfonamides, abuse of laxatives, etc.) may have supply problems. or in situations of inadequate intestinal absorption (for example, due to alterations in the production/secretion of bile or pancreatic enzymes or chronic inflammatory bowel disease).
The first and most obvious sign of a vitamin K deficiency is the appearance of coagulation alterations, resulting in a greater propensity to hemorrhages, which can manifest itself with nosebleeds (bleeding from the nose), hematuria (presence of blood in the urine) and gastrointestinal bleeding (blood in the stool).
This tendency can be greatly aggravated by the simultaneous intake of medicines that interfere more or less directly with other mechanisms of the coagulation process, such as anticoagulant or antiplatelet drugs (used to prevent deep vein thrombosis and arterial thrombosis in people at high cardiovascular risk or already suffering a heart attack or stroke ), or that reduce the protection of the gastric mucosa, such as non-steroidal anti-inflammatory drugs (NSAIDs).
Vitamin K overdose
Natural vitamin K, taken in the context of usual nutrition or produced by intestinal bacteria, is stored in the body without problems or is eliminated in the faeces or urine and never gives rise to symptoms of intoxication.
High doses of synthetic vitamin K taken, for example, through an overdose supplement, can, however, cause toxic effects, due to the accumulation of degradation products in the blood. In these cases, a severe form of anemia called “hemolytic” may arise, which causes the destruction of red blood cells.
It should be noted, however, that the possibility of developing toxicity from excess vitamin K is absolutely remote if you take food supplements authorized by the Ministry of Health, containing calibrated and safe quantities of all essential micronutrients (vitamins and minerals).
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.