- Health and wellness
- 5 views
- What is vitamin K good for?
- Foods rich in vitamin K
- Vitamin K deficiency
- Contraindications
- Frequently asked questions
What is vitamin K good for?
Vitamin K is a fat-soluble nutrient, meaning it dissolves in fats, and is involved in several physiological processes. It is best known for its role in blood clotting, but it also contributes to the activation of proteins involved in bone metabolism and other cellular mechanisms.
The term vitamin K refers to a family of compounds, including the two main forms found in food: vitamin K1, also known as phylloquinone, and vitamin K2, which includes several menaquinones. The two forms share some functions but differ in their dietary sources and certain metabolic characteristics.
A varied diet that includes green leafy vegetables, vegetable oils and other foods containing vitamin K helps meet the body's requirements. It is also important to be aware of possible interactions with certain anticoagulant medications, as in these situations dietary vitamin K intake needs to be managed carefully.
Blood clotting
One of the most important functions of vitamin K is its role in normal blood clotting. This nutrient acts as a cofactor for an enzyme that enables the activation of certain proteins involved in haemostasis, the process through which the body limits blood loss following an injury.
These proteins include several clotting factors produced mainly by the liver. With the help of vitamin K, they undergo a biochemical modification that is necessary for them to perform their function correctly. In the presence of a significant deficiency, the activity of these factors may decrease and blood may take longer to clot.
A sufficient supply of vitamin K therefore contributes to the normal functioning of the mechanisms that control bleeding. However, this does not mean that vitamin K is a blood thinner: its physiological role is linked to the activation of clotting proteins. It is therefore important not to confuse it with anticoagulant or antiplatelet medications, which work through different mechanisms.
People taking vitamin K antagonist anticoagulants, such as warfarin or acenocoumarol, should pay particular attention to maintaining a consistent dietary intake and consult their doctor before significantly changing their consumption of foods rich in this nutrient or starting a supplement.
Bone health
Vitamin K also contributes to the activation of certain proteins involved in bone metabolism. These include osteocalcin, a protein produced by the cells that form bone tissue. Vitamin K contributes to its biochemical modification, which is necessary for it to perform its function correctly within the bone matrix.
Another vitamin K-dependent protein is matrix Gla protein (MGP), which is found in various tissues and is involved in processes that regulate mineralisation. These mechanisms have attracted interest in relation to the possible role of vitamin K in maintaining bone health and calcium balance in tissues.
It is important to distinguish the biological role of vitamin K from the clinical outcomes of supplementation. Although some studies have investigated possible effects on bone mineral density and fracture risk, the available evidence does not allow us to conclude that taking a supplement prevents osteoporosis or definitely reduces fracture risk in everyone.
Maintaining skeletal health requires consideration of several factors, including adequate calcium and vitamin D intake, physical activity and a balanced diet.
Differences between vitamin K1 and K2
Vitamin K1 and vitamin K2 belong to the same family of nutrients, but they differ in their chemical structure and main dietary sources. Both contribute to the activation of vitamin K-dependent proteins, although their metabolism and distribution throughout the body are not identical.
- Vitamin K1, or phylloquinone, is the predominant form in the European diet. It is mainly found in plant-based foods, particularly green leafy vegetables and certain vegetable oils. It is an important source of vitamin K and contributes to normal blood clotting;
- Vitamin K2, or menaquinone, includes a family of compounds identified by abbreviations such as MK-4 and MK-7. It is found in certain animal-based foods and fermented products. The different forms of K2 vary in the length of their side chains and may have different metabolic characteristics.
In general, the main differences are:
- K1: mainly found in spinach, cabbage, broccoli, lettuce and vegetable oils; it is the predominant form in plant-based sources;
- K2: found in certain fermented foods and animal-based products, such as cheese, eggs and meat; it includes several menaquinones;
- Functions: both contribute to the activation of vitamin K-dependent proteins involved in blood clotting and other physiological processes;
- Metabolism: the different forms may have different retention times and distribution patterns, but the available data do not allow them to be considered interchangeable in every situation.
Vitamin K2 has been particularly studied for its possible role in processes involving osteocalcin and matrix Gla protein. Some menaquinones, such as MK-7, have different bioavailability characteristics compared with K1, but this does not mean that they are always superior or that they guarantee protection against arterial calcification.
Foods rich in vitamin K
Vitamin K is found in numerous foods.
- K1 is mainly found in green leafy vegetables and certain vegetable oils;
- K2 is found in varying amounts in fermented foods and some animal-based products.
To obtain this nutrient through your diet, it is useful to alternate vegetables such as spinach, cabbage and broccoli, use vegetable oils in appropriate amounts and vary your protein sources. Some fermented foods can also contribute to menaquinone intake.
Vitamin K is fat-soluble: the presence of fat in a meal may help its absorption. For example, dressing vegetables with an appropriate amount of extra virgin olive oil combines a source of fat with a food rich in vitamin K1.
Table of foods with the highest vitamin K content
Vitamin K content varies depending on the food variety, preparation method and serving size. The following table provides approximate values for common portions, distinguishing the form of vitamin K present where possible. The data are taken from the tables of the Office of Dietary Supplements of the National Institutes of Health and may vary between products and nutritional databases.
| Food | Reference serving | Approximate vitamin K content | Predominant form |
|---|---|---|---|
| Natto, fermented soybeans | About 85 g | 850 µg | K2 (MK-7) |
| Cooked green leafy vegetables, such as kale | Half a cup | About 530 µg | K1 |
| Cooked turnip greens | Half a cup | About 426 µg | K1 |
| Raw spinach | One cup | About 145 µg | K1 |
| Raw kale | One cup | About 113 µg | K1 |
| Cooked broccoli | Half a cup | About 110 µg | K1 |
| Roasted soybeans | Half a cup | About 43 µg | K1 |
| Soybean oil | One tablespoon | About 25 µg | K1 |
| Cooked edamame | Half a cup | About 21 µg | K1 |
| Pine nuts | About 28 g | About 15 µg | K1 |
| Cashews | About 28 g | About 10 µg | K1 |
| Hard-boiled egg | One large egg | About 4 µg | K2 (MK-4) |
Among the foods listed, natto stands out for its vitamin K2 content, while green leafy vegetables are among the most important sources of K1. However, these values should not be interpreted as amounts that must necessarily be reached at every meal: what matters is the overall intake as part of a varied diet.
Walnuts and other nuts may contain vitamin K, but they are generally not among the most concentrated sources. For this reason, if the goal is to increase your intake of this nutrient, it is more useful to regularly include green leafy vegetables and other relevant food sources in your diet rather than relying exclusively on nuts.
Vitamin K deficiency
Vitamin K deficiency is relatively rare in healthy adults who follow a varied diet. However, it may occur when fat absorption is impaired, dietary intake remains very low for prolonged periods or certain medical conditions and treatments are present.
Since vitamin K is necessary for the activation of certain clotting proteins, a significant deficiency may increase the tendency to bleed. Possible signs include frequent bruising, nosebleeds or bleeding gums, and longer blood-clotting times. These symptoms are not specific and may also be caused by other conditions, so they require medical assessment.
Vitamin K also contributes to the activation of proteins involved in bone metabolism. An insufficient supply may therefore affect certain processes involving bone tissue, although the relationship between vitamin K intake and fracture risk is complex and does not allow every skeletal problem to be attributed to a deficiency of this nutrient.
Main causes in adults
In adults, vitamin K deficiency may be associated mainly with conditions that reduce intestinal fat absorption or interfere with the metabolism of this nutrient. It may also be encouraged by a very restrictive diet followed over a prolonged period, if it does not provide an adequate intake.
The main situations to consider include:
- Fat malabsorption: certain intestinal or pancreatic diseases and conditions that alter bile flow may reduce the absorption of fat-soluble vitamins, including vitamin K;
- Gastrointestinal disorders: untreated coeliac disease, inflammatory bowel diseases and other conditions that impair absorption may increase the risk of deficiency;
- Surgical procedures: certain procedures involving the intestines or digestive system may alter nutrient absorption;
- Prolonged use of certain medications: some antibiotics may affect vitamin K status, particularly when combined with other risk factors. Certain medications may also directly interfere with the metabolism of this nutrient;
- Very restricted diet: a diet that lacks variety and is low in vegetables and other sources of vitamin K may contribute to an insufficient intake, particularly when other absorption problems are present.
It is important to distinguish vitamin K deficiency from the effects of vitamin K antagonist anticoagulants, such as warfarin and acenocoumarol. These medications work by interfering with the vitamin K cycle to reduce the blood's ability to clot. Anyone taking them should follow the instructions of their doctor or anticoagulation clinic, without independently changing their dietary intake or starting supplements.
Contraindications
Vitamin K found in food is generally compatible with a varied and balanced diet. The main precautions concern the use of supplements and, above all, people taking vitamin K antagonist anticoagulants.
Vitamin K may interfere with the effects of warfarin and acenocoumarol, medications that reduce blood clotting by acting on the cycle of this nutrient. A sudden and significant increase or decrease in vitamin K intake may alter the effectiveness of treatment and affect the INR value, the parameter used to monitor blood clotting.
People taking these medications should not eliminate vegetables rich in vitamin K or drastically increase or reduce their consumption on their own to improve blood circulation. Generally, the aim is to maintain dietary intake as consistently as possible and follow the instructions of the doctor or anticoagulation clinic.
Another precaution concerns people who take several supplements at the same time. Some multivitamins or combination products may already contain vitamin K, so it is useful to check labels and avoid unnecessary overlap. The amount and form of this nutrient may vary from one product to another.
If you have a medical condition, are pregnant or breastfeeding, or are taking medication, you should consult your doctor or pharmacist before starting supplementation. Supplements should not be used to independently modify anticoagulant treatment or to treat blood-clotting disorders.
Frequently asked questions
Why should vitamin D be taken together with vitamin K?
Vitamin D and vitamin K are involved in different but related processes in calcium metabolism. Vitamin D contributes to intestinal calcium absorption and the maintenance of normal calcium levels in the blood, while vitamin K is necessary for the activation of proteins such as osteocalcin, which is involved in bone metabolism, and matrix Gla protein, which is found in various tissues.
This biological cooperation explains the interest in combining the two nutrients in supplements. However, there is no evidence that everyone should take vitamin D and K together or that this combination automatically prevents arterial calcification. The actual need for supplementation depends on dietary intake, nutritional status and individual circumstances.
Does vitamin K help thin the blood?
No, vitamin K is not a blood thinner. On the contrary, it is necessary for activating certain proteins involved in blood clotting. Its physiological function therefore contributes to the normal processes that allow blood to clot when an injury occurs.
The confusion may arise from the fact that certain anticoagulant medications, such as warfarin and acenocoumarol, work by interfering with the vitamin K cycle. These medications reduce the activation of specific clotting factors, but they do not turn vitamin K into a blood-thinning substance.
People taking vitamin K antagonist anticoagulants should maintain a regular dietary intake of this nutrient and should not independently change their consumption of vegetables rich in vitamin K. The use of supplements should also be agreed with their doctor or the clinic managing their treatment.
Do walnuts contain useful amounts of vitamin K?
Walnuts contain vitamin K, but generally in lower amounts than the main dietary sources, such as spinach, cabbage, broccoli and other green leafy vegetables. They can contribute to overall vitamin K intake, but they are not among the foods with the highest concentrations.
If the goal is to increase vitamin K intake through your diet, it is useful to alternate walnuts with other richer sources, particularly green leafy vegetables and certain cruciferous vegetables. People taking warfarin or acenocoumarol should maintain consistent eating habits and follow their doctor's instructions, without independently eliminating foods containing vitamin K.
Vitamin K is essential for normal blood clotting and contributes to the activation of proteins involved in bone metabolism. It is found mainly in green leafy vegetables in the form of K1, while K2 is present in certain fermented foods and animal-based products. Before using supplements, it is important to consider individual needs and possible interactions with anticoagulant medications.
