What is Vitamin K, and why is it needed?
Vitamin K is a fat-soluble vitamin that plays a vital role in blood clotting, bone metabolism, and cardiovascular health. It is essential for the activation of proteins that regulate blood coagulation (clotting), calcium binding in bones, and the prevention of vascular calcification.
Unlike water-soluble vitamins (like vitamin C and B-complex), fat-soluble vitamins such as vitamin K are stored in body fat and the liver, and are absorbed along with dietary fats.
Table of Contents
Chemical Forms of Vitamin K
Vitamin K refers to a group of structurally similar compounds, but there are three primary forms:
1. Vitamin K1 (Phylloquinone)
Source: Green leafy vegetables
Function: Main form in the diet, critical for blood clotting
Absorption: Occurs in the small intestine with dietary fat
2. Vitamin K2 (Menaquinones)
Source: Fermented foods, animal products, and produced by gut bacteria
Function: Important for bone and cardiovascular health
Subtypes: MK-4 through MK-13, based on the length of their side chains
3. Vitamin K3 (Menadione) – Synthetic
Source: Used in animal feed, not for human supplementation - no longer used for human treatment due to potential toxicity.
Note: Can be toxic in high doses; not recommended for human use.
Functions of Vitamin K
Vitamin K is a fat-soluble vitamin that plays an essential role in blood clotting and bone health. It is a group of structurally similar compounds, with the two main forms being vitamin K1 (phylloquinone) and vitamin K2 (menaquinone).
A. Blood clotting
One of the most important functions of vitamin K is its role in blood clotting. It is required for the production of several proteins involved in the coagulation cascade, which is the series of chemical reactions that lead to the formation of blood clots. Without vitamin K, blood would not be able to clot properly, leading to excessive bleeding or hemorrhaging. This is why newborns are given a vitamin K injection shortly after birth, as they have not yet developed the ability to produce sufficient amounts of vitamin K.
Without vitamin K, the body cannot effectively form blood clots, leading to excessive bleeding, even from minor injuries.
🍼 Newborns are given a vitamin K injection at birth because they are born with low stores, putting them at risk for vitamin K deficiency bleeding (VKDB).
B. Bone Health
Vitamin K is also important for bone health. It helps to activate a protein called osteocalcin, which is involved in the mineralization of bone tissue. Without adequate vitamin K, bones may become weak and brittle, leading to conditions such as osteoporosis.
C. Cardiovascular health
Research has suggested that vitamin K may also play a role in cardiovascular health. Specifically, it may help to prevent the buildup of calcium in the arteries, which is a major risk factor for heart disease. Vitamin K accomplishes this by activating another protein called matrix Gla protein (MGP), which helps to prevent the calcification of arteries.
Inadequate K2 may allow calcium to be deposited in arteries instead of bones, increasing the risk of heart disease.(alert-passed)
D. Brain Health
Emerging research has also suggested that vitamin K may play a role in brain health. Specifically, it may help to protect against age-related cognitive decline and neurodegenerative diseases such as Alzheimer's. This is thought to be due to vitamin K's ability to activate proteins that protect against oxidative stress and inflammation in the brain.
E. Cancer Prevention
Finally, vitamin K may also play a role in cancer prevention. Studies have suggested that it may help to inhibit the growth of cancer cells and reduce the risk of certain types of cancer, such as liver and prostate cancer.
Vitamin K is a crucial nutrient with a wide range of functions in the body. Its importance in blood clotting and bone health cannot be overstated, and emerging research has suggested that it may also play a role in cardiovascular and brain health, as well as cancer prevention.(alert-success)
Vitamin K Cycle
In the body, vitamin K is recycled through a biochemical pathway called the vitamin K epoxide cycle, allowing small amounts to be reused multiple times. This is how the body maintains blood clotting activity even with modest intake.
Here's a detailed breakdown of the cycle:
1. The Starting Point: Active Vitamin K
The biologically active form of Vitamin K required for its primary function is Vitamin K hydroquinone (KH2). This is the reduced form of the vitamin.
2. The Key Job: Carboxylation
Vitamin K hydroquinone (KH2) serves as an essential cofactor for the enzyme gamma-glutamyl carboxylase (GGCX). This enzyme resides primarily in the liver (for clotting factors) but also in other tissues like bone (for bone proteins).
GGCX's job is to modify specific precursor proteins (like prothrombin, factors VII, IX, X, protein C, protein S, osteocalcin, MGP) by adding a carboxyl group (COOH) to certain glutamate (Glu) residues within these proteins. This converts Glu residues into gamma-carboxyglutamate (Gla) residues.
The presence of these Gla residues is critical. They act like tiny "claws" that can bind calcium ions (Ca²ᐩ). This calcium-binding ability allows the proteins (especially clotting factors) to anchor effectively to phospholipid surfaces (like those on platelets or damaged blood vessel walls), which is essential for their biological activity in the blood clotting cascade or bone mineralization.
3. The Consequence: Oxidation
During the carboxylation reaction catalyzed by GGCX, the active Vitamin K hydroquinone (KH2) donates electrons and is simultaneously oxidized into Vitamin K 2,3-epoxide (KO).
4. The First Recycling Step: Reducing the Epoxide
Now, the Vitamin K 2,3-epoxide (KO) is inactive as a cofactor for GGCX. To be reused, it must be converted back to its active form.
The first step in this regeneration is catalyzed by the enzyme Vitamin K epoxide reductase (VKOR), specifically the enzyme complex VKORC1.
VKORC1 reduces Vitamin K epoxide (KO) back to Vitamin K quinone (K). This is a critical step in the cycle.
4. The Second Recycling Step: Back to Active Form
Vitamin K quinone (K) is still not the active form needed for carboxylation. It needs to be reduced further.
Vitamin K quinone (K) is reduced back to the active Vitamin K hydroquinone (KH2). This reduction can also be carried out by VKORC1, or potentially by other cellular reductases that use NADH or NADPH as electron donors.
5. Completing the Cycle
With Vitamin K hydroquinone (KH2) regenerated, it is ready to participate in another round of carboxylation via GGCX, starting the cycle anew.
Significance of the Vitamin K Cycle:
Efficiency: The Vitamin K cycle is highly efficient. It allows a relatively small dietary intake or body pool of Vitamin K to be reused multiple times. Each molecule can potentially participate in many carboxylation reactions before it is eventually metabolized and excreted.
Maintaining Activity: This recycling ensures that the body can maintain adequate levels of active Vitamin K hydroquinone (KH2) to support the continuous synthesis and activation of vitamin K-dependent proteins, even if dietary intake fluctuates moderately day-to-day. This is vital for maintaining normal blood clotting ability.
The Warfarin Connection to Vitamin K:
The anticoagulant drug warfarin (Coumadin) exerts its effect by specifically inhibiting the Vitamin K epoxide reductase (VKORC1) enzyme.
By blocking VKORC1, warfarin prevents the conversion of Vitamin K epoxide (KO) back to Vitamin K quinone (K). This breaks the cycle.
As a result, Vitamin K epoxide (KO) accumulates, and the pool of active Vitamin K hydroquinone (KH2) becomes depleted.
Without sufficient KH2, the gamma-glutamyl carboxylase (GGCX) cannot effectively carboxylate the vitamin K-dependent clotting factors.
This leads to the production of under-carboxylated, inactive clotting factors, which reduces the blood's ability to clot – the therapeutic goal when prescribing warfarin to prevent harmful blood clots.
In essence, the Vitamin K cycle is a vital recycling pathway that ensures the continuous availability of the active form of Vitamin K needed for critical functions like blood clotting and bone metabolism, allowing the body to function effectively even with modest vitamin K levels. Its inhibition by drugs like warfarin underscores its importance in hemostasis.
Vitamin K Interactions with Medications
Vitamin K plays a crucial role in blood clotting, bone metabolism, and cardiovascular health. However, its interactions with medications—especially blood thinners—can be clinically significant and must be managed carefully.
1. Anticoagulants (Blood Thinners)
➤ Warfarin (Coumadin)
Main interaction: Warfarin works by inhibiting vitamin K activity to prevent blood clots. Consuming high or inconsistent amounts of vitamin K (especially K1 from leafy greens) can reduce its effectiveness or cause dangerous fluctuations in INR (a blood clotting measure).
What happens:
🡆 High vitamin K intake → lowers warfarin effectiveness → risk of blood clots
🡆 Low vitamin K intake → increases warfarin potency → risk of bleeding
Recommendation: Maintain a consistent intake of vitamin K-rich foods while on warfarin. Do not eliminate vitamin K; just avoid sudden changes.
Sudden increases or decreases in vitamin K intake can cause dangerous bleeding or clotting events in people on warfarin.(alert-warning)
2. Interaction with Antibiotics
Some antibiotics can reduce vitamin K levels by destroying the gut bacteria that synthesize it, especially in long-term use.
Affected Antibiotics:
🡆 Cephalosporins (e.g., cefoperazone)
🡆 Broad-spectrum antibiotics (like ciprofloxacin, amoxicillin-clavulanate)
What happens:
Reduced vitamin K production → increased bleeding risk
Who’s at risk:
🡆 Malnourished individuals
🡆 Those on prolonged antibiotic courses
🡆 People taking warfarin simultaneously
3. Cholesterol-Lowering Medications
A. Bile acid sequestrants:
🡆 Examples: Cholestyramine, colestipol
🡆 These drugs bind bile acids in the gut to reduce cholesterol but can also bind fat-soluble vitamins, including vitamin K, preventing absorption.
B. Orlistat (Alli/Xenical):
🡆 A weight-loss medication that blocks fat absorption can also reduce the absorption of fat-soluble vitamins like vitamin K.
What happens:
Long-term use → vitamin K deficiency → risk of bruising or bleeding
Recommendation: Supplementation of fat-soluble vitamins may be advised during long-term use under medical supervision.
4. Anti-Tuberculosis Drugs
🡆 Isoniazid and Rifampin
🡆 These drugs may impair vitamin K metabolism in the liver.
Can contribute to bleeding tendencies, especially in malnourished individuals or in infants.
5. Anticonvulsants (Seizure Medications)
🡆 Examples: Phenytoin, phenobarbital, carbamazepine
🡆 Long-term use may reduce vitamin K levels, particularly in newborns of mothers taking these medications.
Newborn Risk: Vitamin K deficiency bleeding (VKDB) → why newborns often receive vitamin K injections at birth
Remember These Tips:
🩺 Consistency is key: For those on anticoagulants, do not dramatically change your vitamin K intake without medical guidance.
🩺 Supplements: Vitamin K supplements should only be taken under supervision if you're on medications that interact with it.
🩺 Always inform your doctor about your diet and supplements when being prescribed or adjusted on medications that affect blood clotting.
Dietary Sources of Vitamin K
There are two main forms of vitamin K: vitamin K1, also known as phylloquinone, which is found in plant foods, and vitamin K2, also known as menaquinone, which is found in animal foods and fermented foods.
🥦 1. Dietary Sources of Vitamin K1 (Phylloquinone)
Vitamin K1 accounts for about 90% of total vitamin K intake in Western diets. It is mainly found in green leafy vegetables and some plant oils.
| Food | Approx. K1 Content (mcg) |
|---|---|
| Kale (cooked) | 817 mcg |
| Spinach (raw) | 483 mcg |
| Collard greens (cooked) | 770 mcg |
| Turnip greens | 600 mcg |
| Broccoli (cooked) | 220 mcg |
| Brussels sprouts (cooked) | 140 mcg |
| Green lettuce (romaine, etc.) | 100–120 mcg |
| Parsley | 1640 mcg |
| Cabbage | 80 mcg |
💡 Tip: Cooking can reduce the vitamin K content slightly, but absorption improves when eaten with fat (e.g., olive oil or butter).
🧈 Plant-Based Oils with Vitamin K1:
- Soybean oil
- Canola oil
- Olive oil
- Cottonseed oil
These oils contribute moderate amounts to overall intake, especially when used in cooking or salad dressings.
🧀 2. Dietary Sources of Vitamin K2 (Menaquinones)
Vitamin K2 exists in several forms, mostly denoted as MK-4 to MK-13, depending on the length of their side chains. It plays a key role in calcium regulation, bone health, and vascular health.
| Food | Type | Approx. K2 Content (mcg/100g) |
|---|---|---|
| Egg yolks | MK-4 | 30 mcg |
| Chicken liver | MK-4 | 14 mcg |
| Butter | MK-4 | 15 mcg |
| Hard cheeses | MK-8/MK-9 | 60–100 mcg |
| Soft cheeses (e.g., Brie) | MK-8/MK-9 | 30–50 mcg |
| Whole milk | MK-4 | ~1–3 mcg |
| Ground beef (grass-fed) | MK-4 | Low–moderate |
The absorption of vitamin K from food sources is enhanced by the presence of dietary fat. Therefore, it is recommended to consume vitamin K-rich foods with a source of healthy fats, such as olive oil, avocado, nuts, or seeds, to ensure optimal absorption.
It is important to note that the bioavailability of vitamin K1 from plant foods is lower compared to vitamin K2 from animal and fermented foods. However, consuming a variety of vitamin K-rich foods can help ensure adequate intake of both forms of vitamin K.
🧬 3. Endogenous Production (Gut Bacteria)
Certain gut bacteria in the large intestine synthesize menaquinones (K2), mainly MK-7 to MK-13. However:
➤ The amount absorbed is uncertain.
➤ Most of this K2 may be used locally in the colon, with minimal systemic absorption.
➤ Still, healthy gut flora may contribute modestly to your vitamin K status.
🌿 A healthy gut microbiome supported by a high-fiber diet and fermented foods may assist in maintaining vitamin K2 levels.
💊 4. Fortified Foods and Vitamin K Supplements
Fortified Foods:
Some breakfast cereals and meal replacement drinks are fortified with vitamin K (more common in North America).
Fortified plant-based milks (e.g., soy, almond) may contain added vitamin K1.
Supplements:
Vitamin K1: Available as phylloquinone tablets or drops.
Vitamin K2:
MK-4 supplements: Shorter half-life, requires multiple daily doses.
MK-7 supplements: Longer half-life, often taken once daily.
Usually derived from natto or synthesized via bacterial fermentation.
✅ Supplements may be recommended for individuals with poor absorption or those on long-term antibiotics, but excessive use should be monitored, especially if taking blood thinners like warfarin.
People on anticoagulants or with absorption issues should consult a doctor before making dietary changes or taking supplements.(alert-warning)
Vitamin K deficiency is a rare condition that can occur in infants, people with digestive disorders, and those taking certain medications.
Vitamin K is a fat-soluble vitamin that plays a vital role in blood clotting, bone metabolism, and other important bodily functions. Vitamin K deficiency can lead to a variety of health problems, including excessive bleeding and poor bone health. There are several causes of vitamin K deficiency, including insufficient dietary intake, poor absorption, and certain medical conditions.
One of the most common causes of vitamin K deficiency is a diet that is low in vitamin K-rich foods. Vitamin K is found in high concentrations in leafy green vegetables such as spinach, kale, and broccoli, as well as in other foods such as liver, egg yolks, and cheese. People who do not consume enough of these foods may be at risk for vitamin K deficiency.
Another cause of vitamin K deficiency is poor absorption of the vitamin due to digestive disorders such as inflammatory bowel disease, celiac disease, or cystic fibrosis. These conditions can cause malabsorption of nutrients, including vitamin K, leading to a deficiency. Additionally, long-term use of antibiotics can disrupt the balance of bacteria in the gut, which can affect the absorption of vitamin K.
Certain medications can also interfere with the body's ability to absorb or utilize vitamin K. Blood thinners, such as warfarin, work by inhibiting the action of vitamin K, which can lead to a deficiency if not properly monitored. Other medications, such as some antibiotics and anticonvulsants, can interfere with the body's ability to absorb vitamin K.
Vitamin K Deficiency in Infants
Newborn infants are at increased risk for vitamin K deficiency for a variety of reasons:
- Breast milk contains low levels of vitamin K
- Vitamin K does not transfer well from the mother’s placenta to the baby
- The liver of a newborn infant does not use the vitamin efficiently
- Newborns can not produce vitamin K2 on their own in the first few days of life
Deficiency of vitamin K leads to hemorrhagic disease in the newborn, which can be prevented by prophylactic vitamin K. Vitamin K (phytomenadione 1 mg, intramuscular injection) is given to all neonates after risks have been discussed with parents, and consent is obtained.
Symptoms of Vitamin K Deficiency
Vitamin K is an essential vitamin that plays a crucial role in blood clotting and bone metabolism. When there is a deficiency of Vitamin K in the body, it can lead to several health problems. Vitamin K deficiency is rare in healthy adults but can occur in newborn babies, people with certain medical conditions, and those who are taking certain medications. The symptoms of Vitamin K deficiency can vary depending on the severity and duration of the deficiency.
One of the main functions of Vitamin K is to help in the blood clotting process. A deficiency of Vitamin K can lead to abnormal bleeding, which can be severe in some cases. The symptoms of abnormal bleeding due to Vitamin K deficiency include:
1. Easy bruising: Vitamin K is necessary for the formation of blood clots, which helps to stop bleeding under the skin. A lack of Vitamin K can cause easy bruising, even with minor injuries.
2. Nosebleeds: Frequent nosebleeds or bleeding from the gums can be a symptom of Vitamin K deficiency.
3. Heavy menstrual bleeding: Women with Vitamin K deficiency may experience heavy menstrual bleeding.
4. Blood in the urine or stool: Vitamin K deficiency can cause bleeding in the urinary tract or gastrointestinal tract, leading to blood in the urine or stool.
5. Prolonged bleeding: In severe cases of Vitamin K deficiency, bleeding may not stop on its own, and medical intervention may be required to stop the bleeding.
Apart from the bleeding symptoms, Vitamin K deficiency can also affect bone health, as it is involved in bone metabolism. The symptoms of Vitamin K deficiency related to bone health include:
1. Osteoporosis: Vitamin K is required for the production of a protein called osteocalcin, which helps to bind calcium to bones. A deficiency of Vitamin K can lead to decreased bone density and osteoporosis.
2. Increased risk of fractures: With decreased bone density, the risk of fractures increases.
3. Dental problems: Vitamin K deficiency can lead to dental problems, such as tooth decay and gum disease.
4. Joint pain: A lack of Vitamin K can lead to joint pain and stiffness.
In newborn babies, Vitamin K deficiency can lead to a serious condition called Vitamin K deficiency bleeding (VKDB). VKDB can cause bleeding in the brain and other organs, which can be life-threatening.
Complications of Vitamin K Deficiency
One of the most significant complications of vitamin K deficiency is an increased risk of bleeding. This is because vitamin K is necessary for the synthesis of several clotting factors, including prothrombin, factors VII, IX, and X, and proteins C and S. Without adequate vitamin K, these clotting factors cannot be produced, and the body is unable to form clots in response to injury or other causes of bleeding.
Vitamin K deficiency can also lead to osteoporosis, a condition in which bones become weak and brittle. This is because vitamin K is required for the synthesis of osteocalcin, a protein that is important for bone formation and mineralization. Without adequate vitamin K, the body is unable to produce enough osteocalcin, which can result in decreased bone density and an increased risk of fractures.
In addition to its role in blood clotting and bone metabolism, vitamin K has also been shown to play a role in preventing cardiovascular disease. Studies have suggested that vitamin K may help prevent the calcification of arteries, which can lead to heart disease and stroke.
Finally, some research has suggested that vitamin K may have anti-inflammatory properties and may help to prevent or alleviate certain conditions that are associated with chronic inflammation, such as rheumatoid arthritis.
Diagnosis of Vitamin K Deficiency
Diagnosing Vitamin K deficiency can be challenging as it may present with non-specific symptoms. Moreover, the symptoms of Vitamin K deficiency are not specific to the deficiency, and they may occur due to other health conditions as well. Therefore, healthcare providers need to evaluate a patient's medical history, symptoms, and physical examination results to diagnose Vitamin K deficiency.
Medical History
A healthcare provider may ask a patient about their medical history, including any medications they are currently taking, any medical conditions they have, or any surgeries they have undergone. Some medical conditions or surgical procedures may interfere with the absorption or utilization of Vitamin K in the body, leading to deficiency. Additionally, some medications, such as blood thinners, can interfere with Vitamin K's role in blood clotting and increase the risk of bleeding disorders.
Physical Examination
A physical examination can provide valuable information in diagnosing Vitamin K deficiency. A healthcare provider may look for signs of bleeding, such as bruising or petechiae, which are small red or purple spots on the skin caused by bleeding under the skin. Additionally, they may check the patient's joints for swelling, which can be a sign of internal bleeding.
Laboratory Tests
A healthcare provider may order laboratory tests to confirm the diagnosis of Vitamin K deficiency.
These tests include the prothrombin time (PT) and activated partial thromboplastin time (aPTT) tests, which measure the time it takes for blood to clot.
Normal Values:
- Prothrombin Time (PT) - Normal PT is: 11 - 13.5 seconds
- Activated Partial Thromboplastin Time (aPTT) test normal value: 26-37 seconds
- International Normalized Ratio (INR) - Normal INR is 1.0 -1.3
Patients with Vitamin K deficiency may have an increased PT or aPTT due to the reduced ability of their blood to clot properly. Additionally, a healthcare provider may order a Vitamin K blood test to measure the level of Vitamin K in the patient's blood.
It is important to note that the diagnosis of vitamin K deficiency may be complicated by the fact that vitamin K deficiency often occurs alongside other nutritional deficiencies, such as deficiencies in vitamin C or iron. As a result, doctors may need to conduct additional tests to rule out other potential causes of bleeding disorders.
Management of Vitamin K Deficiency
The management of vitamin K deficiency involves identifying the underlying cause and correcting it, as well as ensuring adequate intake of vitamin K through dietary sources or supplements.
The first step in managing vitamin K deficiency is to identify the underlying cause. This may involve evaluating the patient's diet, medical history, and medications. Patients who have a poor diet or take medications that interfere with vitamin K absorption may need to modify their lifestyle or switch to alternative medications.
If the cause of the vitamin K deficiency is related to malabsorption, then the patient may need to be treated with vitamin K supplements. Vitamin K supplements come in different forms, including oral capsules and injectable solutions. Patients who are unable to take supplements orally may need to receive vitamin K injections.
Patients who have severe bleeding or are at risk of bleeding may require immediate treatment with vitamin K. This may involve administering high doses of vitamin K through an intravenous injection or infusion. In some cases, blood transfusions or other medical interventions may be necessary.
Patients who have liver disease or other conditions that impair vitamin K synthesis may need to receive long-term vitamin K supplementation. This may involve taking vitamin K supplements daily or receiving periodic injections or infusions.
Dietary changes can also help to manage vitamin K deficiency. Foods that are rich in vitamin K include leafy green vegetables, such as spinach and kale, as well as broccoli, Brussels sprouts, and other cruciferous vegetables. Fermented foods, such as natto and sauerkraut, are also good sources of vitamin K.
Prevention of Vitamin K Deficiency
Vitamin K deficiency can lead to bleeding disorders and bone loss, so it is essential to consume adequate amounts of this nutrient to prevent deficiency.
Here are some ways to prevent Vitamin K deficiency:
Consume a variety of Vitamin K-rich foods
The most abundant sources of Vitamin K are green leafy vegetables, such as spinach, kale, collards, and broccoli. Other sources include Brussels sprouts, asparagus, green beans, peas, cabbage, cauliflower, and avocado. Animal products, such as eggs, liver, and meat, also contain small amounts of Vitamin K.
Include fermented foods in your diet
Fermented foods, such as sauerkraut, pickles, kimchi, and kefir, are excellent sources of Vitamin K2, a form of Vitamin K that is essential for bone health.
Take Vitamin K supplements
If you are unable to consume enough Vitamin K in your diet, you may need to take supplements. Vitamin K supplements are available in both synthetic and natural forms. The natural form, Vitamin K2, is more easily absorbed by the body and may be more effective at preventing deficiency.
Be cautious when taking certain medications
Some medications, such as blood thinners, can interfere with Vitamin K absorption and increase the risk of deficiency. If you are taking any medications, speak with your healthcare provider to determine if you need to increase your Vitamin K intake.
Practice good gut health
The bacteria in your gut play a crucial role in Vitamin K production and absorption. Eating a diet rich in fiber and probiotics, such as yogurt and kefir, can promote healthy gut bacteria and improve Vitamin K absorption.
Avoid excessive alcohol consumption
Heavy alcohol consumption can impair Vitamin K absorption and increase the risk of deficiency. Limiting alcohol intake to moderate levels is essential for maintaining optimal Vitamin K levels.
Vitamin K is an essential nutrient that plays a crucial role in blood clotting and bone health. To prevent Vitamin K deficiency, it is essential to consume a variety of Vitamin K-rich foods, including green leafy vegetables and fermented foods
