What is vitamin K?
Vitamin K is actually not just a single vitamin. One would rather speak of the K vitamins, because the important vital substances with vitamin K effectiveness include not only vitamins K1 and vitamin K2, but also synthetically produced vitamin K3.
The K in the name of the K vitamins stands for coagulation. In medicine, coagulation is the clotting of blood. This shows the important role vitamin K plays in blood clotting. Just like vitamins E, D and A, K vitamins are also fat-soluble vitamins.
Vitamin K history
The Danish scientist Carl Peter Henrik Dam was the discoverer of the vital substance. He researched cholesterol synthesis in chicks in the 1920s and gave the animals a cholesterol-free diet. After about 2 weeks, he noticed that the test animals had bleeding in the muscles, skin and other organs.
Since Dam was able to rule out a lack of other vitamins, he concluded from these observations that a lack of a previously unknown substance must have caused this bleeding. He called this substance vitamin K.
After many feeding attempts, Dam realized that vitamin K is an essential and fat-soluble vitamin. The chemical structure was elucidated at the Berkeley University in California in the late 1930s. Henrik Dam and Edward Adelbert Doisy, who carried out the structural elucidation, received the Nobel Prize in Medicine for the discovery of the vitamin.
Differentiation K1, K2, K3
Even if only vitamin K is mentioned often, it is a whole vitamin group. More than 100 compounds are known to have a vitamin K efficacy. However, only 3 of these substances are important for the human body.
While vitamins K1 and K2 are naturally occurring vitamins, vitamin K3 is a synthetically produced substance.
This vitamin is also known as phylloquinone. It is primarily part of the so-called chloroplasts that occur in green plants. In plants, phylloquinone is involved in photosynthesis, in humans the body uses the vitamin to produce clotting factors in the liver.
Another name for vitamin K2 is menaquinone. Around half of the vitamin K requirements in healthy people is provided by the production of vitamin K2 by the bacteria in the human intestinal flora, for example by Escherichia coli or Bacteroides fragilis. But fermented dishes like natto also contain vitamin K2.
Just like vitamin K1, the body also needs vitamin K2 for the blood to work properly. The substance also acts as a cofactor in bone metabolism and appears to play a role in the prevention of vascular calcification (arteriosclerosis).
Vitamin K3, also called menadione, is not a naturally occurring substance. The artificial vitamin is obtained through an oxidation process of 2-methylnaphthalene with nitric acid or chromic acid.
Menadione in its water-soluble form was previously used in medicine. However, due to its toxic effects, the synthetic vitamin is no longer used today. Menadione can interfere with the function of glutathione and thereby damage the cell walls. As menadione is therefore no longer approved for medical use, vitamin K deficiency is usually treated by supplementation with phylloquinone (vitamin K1).
Vitamin K in food
There are plenty of foods that contain vitamin K. The vitamin is mainly found in green vegetables. For example, green cabbages such as brussel sprouts or kale contain a relatively large amount of vitamin K. It is important to know that this is vitamin K1.
The body can actually better absorb vitamin K2. However, this vitamin form is only contained in significant amounts in a few foods. In addition to meat and eggs, this also includes dairy products. Natto has a particularly high content of vitamin K2. Natto is a traditional Japanese product made from fermented soybeans.
Vitamin K in food in micrograms per 100 grams: [[C496]]
It should be noted that not all of the vitamin K can be absorbed through the diet. The absorption rate also depends on the intestines condition. Cooking losses of up to 50 percent must also be taken into account.
Fruits and vegetables
- Cress: 541
- Raw spinach: 483
- Kale: 390
- Broccoli: 224
- Brussel sprouts: 177
- Green beans: 38
- Currants: 20
- Blueberries: 17
Meat and fish
- Tuna (in oil): 7
- Turkey: 4.5
- Chicken: 4.5
- Beef: 1.7
Milk, dairy products and eggs
- Butter: 7
- Egg: 4.5
- Cream: 3.2
- Mozzarella: 2.3
- Feta cheese: 1.8
- Milk: 0.5
Vitamin K from the intestine
Vitamin K2 is produced by the bacteria in the intestine. In addition to various strains of Escherichia coli, this also includes bacteria from the Bacteroides fragilis group. How much and whether sufficient vitamin K is produced in the intestine depends above all on a healthy intestinal flora. If there is a dysbiosis with a lack of vitamin-producing bacteria, a vitamin deficiency can quickly develop.
Both vitamin K from food and K2 from the intestine reach the liver via the intestinal wall and the portal vein. There, the inactive precursors of the vital coagulation factors are converted into their active form using the vital substance.
Vitamin K effect
The most important task of vitamin K in the human body is blood clotting. Without the vitamin, the body can't produce active coagulation factors. Without coagulation factors, we would bleed to death very quickly if injured.
But not only the function of the coagulation factors depends on an adequate vitamin K level. The protein osteocalcin, which regulates the mineralization of the bones, also relies on the vitamin.
Vitamin K has other important effects and functions in the body:
- it prevents limescale deposits in soft tissues such as arteries or cartilages
- it regulates cell division and cell migration
- it is involved in numerous repair processes
Vitamin K forms
The K vitamins essentially differentiate between vitamin K1, vitamin K2 and vitamin K3. These vary with regard to their chemical structure and sometimes have different effects.
With regard to the fine structure, further differentiations can be made for both vitamin K1 and vitamin K2. The most common forms include:
- MK7 all-trans
- MK7 cis
The MK9 variant has not been researched a lot and is only approved as a dietary supplement in the USA. Vitamin K MK4 is only effective in high doses, so that only the MK7 form is of therapeutic interest. However, caution is required here, because not all variants of the MK7 form can be used by the body.
The difference between MK7 all-trans and cis
Vitamin K2 MK7 is currently considered the form of the vitamin that has the highest bioavailability. However, this only applies to MK7 all-trans and not for MK7 cis. From a chemical point of view, both forms are identical, they only differ in a small geometric molecular structure.
In order to be fully effective, the vitamin molecules must dock on the cell wall. While the receptor on the cell wall and the vitamin K2 MK7 all-trans fit together like a key and lock, the cis form can be more difficult to dock. [[C497]]
Ideally, a dietary supplement that effectively contributes to the supply of vitamin K should have little to no cis content.
Vitamin K needs
The exact need for vitamin K is still not fully known. It is believed that the body needs around 1 microgram of vitamin K per kilogram of body weight daily. The average daily requirement is 80 micrograms. [[C498]]
However, recent studies assume that this is not sufficient. The above calculations are based on the (outdated) assumption that vitamin K is only important for blood clotting. Taking all tasks into account, many scientists rate the need significantly higher. The optimal estimated need is therefore 150 to 200 micrograms per day. [[C499]]
The German Society for Nutrition (DGE) remains well below this amount with its recommendations. It recommends (in micrograms per day): [[C500]]
- Infants up to 4 months: 4 mcg
- Infants from 4 to 12 months: 10 mcg
- Children and adolescents up to 15 years: 15 to 50 mcg
- Adults under 65 years: 60 to 70 mcg
- Adults over 65 years: 65 to 80 mcg
- Pregnant women: 60 mcg
- Breastfeeding: 60 mcg
Vitamin K deficiency
Vitamin K is contained in many foods, so the need should be met with a balanced diet. However, various factors can affect food content and vitamin intake but may require supplements.
On the one hand, fruits and vegetables lose vital substances when stored for a long time. Part of the vitamin is also destroyed during cooking. The intestine must be intact in order to be able to absorb vitamin K. Disorders in the microbiome, e.g. in the intestinal flora, can impair the absorption. Even with a sufficient supply, the amount actually consumed can be too small.
A not inconsiderable part of the vitamin K requirement is also covered by the production of vitamin K by intestinal bacteria. If there are too few of these vitamin-producing bacteria, a deficiency can arise that can't be compensated for by food.
Deficiency symptoms and causes
Many other factors can contribute to the development of a defect. This includes:
- Chronic liver diseases such as hepatitis B or C
- (Chronic) stomach and intestinal diseases such as chronic diarrhea or inflammatory bowel diseases such as Crohn's disease and ulcerative colitis
- Cystic fibrosis (cystic fibrosis)
- Taking antibiotics or bile acid-binding drugs and taking coumarin derivatives (vitamin K antagonists)
- Pronounced overweight
Vitamin K is involved in the formation of several coagulation factors in the liver. In addition to factor II, this also includes factor VII and the proteins C, S and Z. If there is a lack of vitamin K, these coagulation factors are only produced to an insufficient extent.
Ultimately, this leads to a prolonged blood clotting time and associated blood loss, wound healing disorders, anemia and increased formation of bruises (hematomas) even with minor injuries.
In addition to this, vitamin K also has a function in calcium metabolism and counteracts the calcification of tissues and bones. A lack of vitamin K therefore promotes the development of the following diseases:
- Vascular calcification (arteriosclerosis)
- Osteoporosis (bone loss)
- Arthritis (joint inflammation)
Furthermore, a lack of vitamin K can ensure that the hormone insulin can no longer exert its effects on the body cells. With this so-called insulin resistance, too much sugar remains in the blood. Insulin resistance is the main cause of the development of the metabolic disease diabetes mellitus type 2.
Vitamin K deficiency in babies
During pregnancy, hardly any vitamin K is transferred from the mother to the child via the placenta. Babies with a very low blood level of vitamin K are born. With the exception of colostrum, there is hardly any vitamin K in breast milk. Artificial baby food, on the other hand, is enriched with vitamin K.
To prevent blood clotting disorders in newborns and the associated life-threatening bleeding, children are injected with vitamin K or given it orally shortly after birth. The dose here is 3 times 2 milligrams. However, not all experts consider these high single doses to be advisable.
An alternative is the continuous and lower-dose administration of 25 to 50 micrograms of vitamin K over a period of 12 weeks. This prophylaxis can also be supplemented by a single, slightly higher dose of 1 to 2 milligrams immediately after birth. [[C501]]
It is currently controversial whether the vitamin K content in breast milk can be increased with a vitamin K supplementation. While Saga et al. achieved good results with the administration of the vitamin in their 1989 study, Pietschnig et al. could not confirm these results. Further research would be desirable here. [[C502]] [[C503]]
Vitamin K and blood clotting
Blood clotting (hemostasis) is a vital process that stops bleeding caused by injuries. This prevents too much blood from escaping from the circulation and causing a life-threatening shock. Blood clotting is also an important prerequisite for wound healing.
Primary and secondary blood clotting
Blood clotting can be divided into two processes. In primary hemostasis, platelets (thrombocytes) attach to the cell walls of the injured blood vessel and narrow it. More platelets attach to each other, stick together and thus provide a first temporary closure of the wound.
In secondary hemostasis, fibrin threads increase this occlusion. For this, the coagulation factors that are contained in the blood plasma must be activated. Vitamin K plays a role especially for this secondary hemostasis.
Coagulation factors and vitamin K
Secondary hemostasis creates a wickerwork of fibrin that contains platelets and red blood cells. A coagulation cascade must be started so that this red thrombus, which closes the wound securely, can develop. The first coagulation factors in the blood are activated by proteolytic cleavage.
These activated coagulation factors in turn activate other factors, so that a self-reinforcing process, a so-called coagulation cascade, is created. If there are disturbances in this cascade, the hemostasis does not work or only works insufficiently.
Vitamin K enables the body to convert coagulation factors II, VIII, IX and X into an active form. If there is a lack of vitamin K, the coagulation factors can't be activated to a sufficient extent and the cascade stalls.
In addition to this, vitamin K is also involved in the production of the C and S proteins. These are synthesized in the liver and act as anticoagulants. Vitamin K is not only part of the hemostasis but generally plays an important role in regulating blood clotting. [[C504]] [[C505]]
Vitamin K and coumarin therapy
The influence of vitamin K can therefore interfere with blood clotting. Coumarin derivatives such as warfarin are used primarily for this purpose. These inhibit the activation of coagulation factors II, VII, IX and X by the vitamin. They are therefore also called vitamin K antagonists.
Coumarin derivatives are used to inhibit blood clotting and to prevent blood clots and embolisms. The indications include, above all, chronic atrial fibrillation. The doctor also prescribes coumarin derivatives for heart valve replacements to reduce thrombus formations and the associated increased risk of a stroke.
As a result of the ingestion, even relatively minor injuries can result in relatively large hematomas. Bleeding in different organ systems is also possible. An overdose can therefore lead to life-threatening bleeding.
For a therapy with coumarin derivatives, the intake of vitamin K is absolutely contraindicated. Even small amounts of 1 to 2 milligrams cancel the effect of the vitamin K antagonists. On the other hand, this mechanism can be used if the bleeding tendency in coumarin derivative patients has to be reduced due to an upcoming surgery. [[C506]]
The vitamin K that is ingested with the food reaches the intestinal tissue through active transport and diffusion. From there it is transported to the liver. Vitamin K can store this over a period of 14 days.
Before vitamin K can be effective in the organism, it must first be activated. This happens in a certain part of the cell, the so-called endoplasmic reticulum. Here the vitamin K from food is converted into the active form vitamin K hydroquinone.
Vice versa, a conversion from the active to the non-active vitamin form is also possible. In the vitamin K cycle, also known as the vitamin K metabolism, the vitamin can switch between its two forms.
Certain medications can interfere with this vitamin K cycle and hinder its conversion to the active form. These include, for example, the anticoagulants warfarin and marcumar. But some antibiotics also disrupt the metabolism. This can lead to symptoms of deficiency despite sufficient intake.
Vitamin K and bones as well as joints
For a long time, it was assumed that vitamin K only plays a role in blood clotting. However, it is now clear that the tasks and functions of the vital substance go beyond that. In addition to blood clotting, the vitamin is also involved in bone metabolism. Vitamin K2 in particular is relevant for the health of the skeleton and joints.
The vitamin acts as a co-factor in the activation of certain proteins. In addition to osteocalcin, this also includes the matrix Gla protein.
The peptide hormone osteocalcin is formed in the bone and binds calcium and hydroxyapatite. It is an important marker of bone formation and contributes to the stability of the bones. The matrix Gla protein prevents the calcification of cartilage and the walls of the vessels.
Vitamin K2 therefore helps ensure that calcium from food is stored in the bones and not in the joints or arteries. Thus, the vital substance not only has a positive effect on bone and joint health, but also protects the cardiovascular system.
Vitamin K and osteoporosis
In osteoporosis, popularly known as bone loss, the bones lose strength and become brittle. As a result, bone fractures occur for no apparent reason. After the menopause, women are particularly often affected by osteoporosis due to the hormonal change.
While the administration of vitamin K in Germany for osteoporosis is not yet widespread, supplementation has long been a standard medication in other countries such as Japan. Various scientific studies suggest that the combination of vitamin D and vitamin K in particular can improve bone health and bone stability.
Calcium and vitamin D are also often prescribed in Germany against osteoporosis. However, various scientific studies show that the administration of calcium and vitamin D can reduce the risk of broken bones, but at the same time increases the risk of arteriosclerosis. This is where vitamin K comes in, because it counteracts the deposits in the vessels and promotes the incorporation of calcium into the bones.
Several studies show that the simultaneous administration of vitamin D, calcium and vitamin K can reduce the risk of a bone fracture without increasing the risk of calcification of the vessels. [[C508]] [[C509]]
Vitamin K2 for healthy joints
Vitamin K-dependent proteins such as the matrix gla protein are not only found in the bone, but also in the cartilage. Inadequate activation of these proteins appears to have a negative effect on the condition of the cartilage and thus on joint health.
Various studies have shown a clear connection between the vitamin K status and the occurrence of joint diseases. Study participants in a clinical study with a low vitamin level in plasma, for example, suffered more frequently from cartilage and meniscus damage in the knee as compared to study participants with a sufficiently high vitamin level. [[C510]]
Vitamin K and rheumatoid arthritis
The rheumatoid arthritis is a disease of the rheumatic type. The disease, also known as chronic polyarthritis, is associated with joint pain and joint swelling.
Japanese scientists investigated the influence of vitamin K2 MK4 on the spread of synovial fibroblasts in rats. These activated synovial fibroblasts are largely responsible for the cartilage-degrading processes in rheumatoid arthritis.
In animal experiments, vitamin K2 inhibited the activity and spread of these synovial fibroblasts. This indicates that the vital substance could be used in the therapy of rheumatoid arthritis after further research. [[C511]]
Vitamin K and vascular calcification
Vascular calcification, also called arteriosclerosis in medicine, is one of the main causes of heart attack, stroke and other circulatory disorders. With the disease, deposits and calcifications develop in the arterial walls. These so-called plaques ensure that the very elastic vessel wall is not only thicker, but also more rigid.
As a result, the blood can no longer flow through the affected vessels as well. Circulatory disorders occur. There is also the risk that a blood clot (thrombus) forms which completely closes the vessel. Such a vascular occlusion in the coronary arteries leads to a heart attack. If vessels in the brain are closed, one speaks of a stroke.
The main risk factors for the development of arteriosclerosis include:
- Diabetes mellitus
- Increased levels of LDL cholesterol in the blood
- Increased levels of triglycerides in the blood
The plaques in the blood vessels mainly consist of cholesterol and calcium. By activating the matrix gla protein, vitamin K2 can counteract the accumulation of calcium in the vessels.
A large study published in the specialist magazine Atherosclerosis in 2009 showed a clear connection between vitamin K and arteriosclerosis. The more vitamin K2 the subjects ingested, the less their arterial calcification. However, the researchers found no connection between vitamin K1 and arteriosclerosis.
The Rotterdam Heart Study also examined the relationship between vitamin K and vascular health. For this, more than 4,000 study participants were accompanied over an average period of 10 years. Study participants who consumed a comparatively large amount of vitamin K2 through their diet had a lower risk of cardiovascular diseases than the study participants who consumed comparatively little vitamin K. [[C512]]
The aorta (main artery) showed less calcification and the overall mortality rate was lower. After this long-term study, the researchers concluded that vitamin K2 plays an important role in the prevention of arteriosclerosis and the development of cardiovascular diseases. [[C513]]
Vitamin K for existing calcifications
Vitamin K is not only suitable for preventing a hardening of the arteries. The vital substance also seems to have an effect on existing plaques in the vessels. In an animal study, the scientists administered warfarin to the anticoagulant, thereby inducing vascular calcifications.
Some of the rats were given food containing vitamin K2, the other rats were fed normally. Compared to the control group, the rats in the K2 group had 50 percent fewer calcifications after 6 weeks. [[C514]]
Vitamin K and diabetes
With the metabolic disease diabetes mellitus (diabetes), the blood sugar level is permanently pathologically increased. While type 1 diabetes is based on an absolute insulin deficiency, type 2 diabetes is based on insulin resistance.
The hormone insulin is formed in the pancreas and ensures that the sugar from the blood reaches the cells. If, due to an unbalanced diet or a lack of exercise, there are severe fluctuations in blood sugar and thus increased insulin secretion, the cells become resistant.
The pancreas continues to release insulin, but the cells stop responding. As a result, the sugar remains in the blood and does not reach the cells. The abnormally high blood sugar levels lead to the following symptoms:
- increased urge to urinate
- strong thirst
- weakness, tiredness and difficulty concentrating
- visual disorders
- itching and poor wound healing
- increased infection tendency
In the long term, the blood vessels and nerves are also damaged. Patients suffer from impaired pain sensation, have sensations or digestive problems. The brain, heart and other organs are no longer adequately supplied with oxygen and the risk of life-threatening diseases such as a heart attack or a stroke increases significantly.
Given these drastic consequences, it is important to lower the risk of diabetes in high-risk patients. Vitamin K2 can contribute to this prevention. Studies show that the vitamin can improve insulin and glucose metabolism. This preventive effect is presumably based on the activation of the proteins osteocalcin and MGP (matrix gla protein).
Not only does osteocalcin play a role in bone health, it also directly stimulates insulin production in the Langerhans Islands of the pancreas. It also promotes the release of adiponectin. This peptide hormone, which is produced in the fat cells, increases the insulin effect. A lack of adiponectin increases the risk of diabetes. Vitamin K can therefore increase insulin sensitivity and counteract insulin resistance. [[C515]] [[C516]]
Vitamin K and intestinal flora
The entirety of all microorganisms living in the intestine is called intestinal flora or microbiome. In a healthy adult, around 100 trillion bacteria of 200 to 300 different species colonize the digestive organ. These bacterial strains include, for example firmicutes, bacteroidetes or proteobacteria.
These bacteria don't just play a role in gut health. They:
- modulate the immune system
- stimulate intestinal peristalsis
- produce short chain fatty acids
- improve overall performance
- produce various vitamins such as vitamin K, thiamine, B12 and riboflavin
Vitamin K and dysbiosis
We speak of a dysbiosis when the intestinal flora is out of balance. The main reasons for this are an unbalanced diet and the use of antibiotics. As a result, harmful bacteria spread and displace the desired bacteria. There are putrefactive processes in the intestine, the food is no longer used appropriately and there is a lack of important nutrients.
Dysbiosis has two negative effects on the vitamin K supply. On the one hand, vitamin K from food can no longer be absorbed so well if there is an imbalance in the intestine. On the other hand, the bacteria that produce vitamin K are lacking.
If you suffer from dysbiosis, you should consider supplementing with vitamin K. The following symptoms indicate an imbalance in the intestine:
- Stomach pain
- Food intolerance
Vitamin K and cancer
Every year around 500,000 people in Germany fall sick to cancer. The most common types of cancer include prostate cancer, colon cancer and breast cancer. In 2014, one in four deaths was due to cancer and the trend is rising.
The exact cause of many cancers is still unknown. However, recent research suggests that cancer in many cases is promoted by an unhealthy lifestyle. According to estimates, 30 percent of all cancers can be attributed to poor nutrition. The proportion is as high as 70 percent in gastrointestinal tract cancers. [[C517]]
This is why more and more research is devoted to the relationship between vitamins and cancer. Vitamin K also appears to play a role in the prevention of cancer. The results of the EPIC study suggest that vitamin K could protect against cancer.
More than 20,000 people between the ages of 35 and 64 participated in the study. They have been examined regularly since 1994 and observed for cancer incidence and cancer mortality. Using questionnaires, the researchers also assessed the intake of vitamin K through food.
There was an inverse correlation between the intake of vitamin K2 and the incidence of cancer, e.g. the frequency of cancer events in the group of study participants: Subjects who consumed more vitamin K2 were less likely to develop cancer. This correlation was more pronounced in men than in women and primarily related to prostate and lung cancer. [[C518]]
Vitamin K as a food supplement
As a dietary supplement, vitamin K can prevent and counteract deficiency symptoms. However, there are a few points to consider when choosing the right preparations.
Vitamin K1 and K2 differ in their effects. While vitamin K1 mainly works in blood clotting, vitamin K2 plays a role in bone, joint and vascular health. Vitamin K2 is also primarily used in the prophylaxis of cancer and metabolic diseases such as diabetes mellitus. If you want to strengthen your bones, you should supplement vitamin K2.
When buying food supplements, you should make sure that the vitamin is in the MK7 form. The cis content should ideally be low, at best it is an all-trans preparation. The easiest way for the body to utilize this.
Vitamin K2 is often available in combination with vitamin D because both vital substances work synergistically. Among other things, vitamin D promotes the absorption of calcium from food, whereas vitamin K2 ensures that this calcium gets into the bones and does not calcify the arteries. [[C519]]
Vitamin K dosage form
Vitamin K is available as a dietary supplement in various forms. The vital substance is available as a capsule, in drops or in powder form.
Drops are the ideal variant for children and teenagers. They are easy to dose and can be swallowed quickly. Adults who don't want to swallow capsules can also use this. An advantage of the drops is that they usually contain oil. This way, the fat-soluble vitamin can be better absorbed in the intestine.
Capsules are also good for vitamin supply. They contain a standardized amount of vitamin K and can therefore be dosed safely. To improve absorption, the capsule can be taken with a teaspoon of oil.
Vitamin K side effects
In the recommended dosage, vitamin K usually has no side effects. The Food and Nutritional Board (FNB) in the USA has not established any upper limits for vitamin K due to its low toxicity potential . In its report, the FNB determined that there were no side effects in connection with the intake of vitamin K in the form of food or food supplements in humans or animals.
Vitamin K overdose and interaction
In newborns, an overdose can trigger red blood cell breakdown (hemolysis). No negative effects were observed in adults even at a higher dose.
There are interactions with various drugs [[C521]]
- Warfarin and other anti-coagulants: Vitamin K can reduce or completely eliminate the anticoagulant effects of these medicines.
- Antibiotics: Antibiotics can intervene in the vitamin K cycle and decimate the vitamin-producing bacteria in the intestine. This can lead to deficiency symptoms.
- Choletyramine: These medications inhibit the absorption of cholesterol. At the same time, they also prevent the absorption of fat-soluble vitamins such as vitamin K. Even with a sufficient intake, this can lead to a vitamin deficiency.
- Orlistat: Orlistat is a medication used to treat obesity. It reduces the absorption of fat and thus the absorption of fat-soluble vitamins.