Vitamin K

    Researchedby:
    Thomas Solomon

    Fact-checked

    by:

    Nick Milazzo
    Last Updated: August 8, 2024

    Vitamin K is a fat-soluble vitamin that plays a key role in blood coagulation, bone metabolism, and vascular health. Vitamin K1 is found in many leafy greens and soy, while vitamin K2 is found in meat and fermented foods and is synthesized by intestinal bacteria. Supplementation with vitamin K improves markers of bone health, and vitamin K is administered to newborns to prevent vitamin K deficiency bleeding.

    What is vitamin K?

    Vitamin K is an essential vitamin that plays an important role in blood coagulation, bone metabolism, and vascular health, and it is one of the four fat-soluble vitamins (along with vitamin A, vitamin D, and vitamin E).[10][11][12] Vitamin K is actually the collective term for several fat-soluble molecules called 2-methyl-1,4-naphthoquinones.[10][11][12]

    There are two naturally occurring forms of vitamin K: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). K1 is the major dietary form and is found in several plant-based foods including spinach, broccoli, kale, Brussels sprouts, collards, and soybeans.[6][10][11][12] Vitamin K2 is synthesized by bacteria — including gut bacteria in our microbiome — and is found in meat and fermented foods (e.g., nattō; fermented soybeans).[13][8][10][11][12]

    Phylloquinone (vitamin K1) is the predominant form used in vitamin K supplements, but menaquinones (vitamin K2) are also used.[10][14] Another form of vitamin K called menadione (or vitamin K3) is an intermediate molecule in vitamin K metabolism.[10][12][15] It is not typically used in human supplements, but it is used in animal feed.[16]

    What are the signs and symptoms of vitamin K deficiency?

    What causes vitamin K deficiency?

    What are vitamin K’s main benefits?

    Due to vitamin K’s role in blood coagulation, bone metabolism, and vascular health,[10][11][12] supplementation with vitamin K is claimed to have a range of benefits on blood clotting (coagulation), bone health, cardiovascular health, diabetes and blood sugar, and cancer.

    The main benefit of vitamin K supplementation is in newborn babies, because vitamin K deficiency bleeding (VKDB) can arise due to inadequate vitamin K storage or a vitamin K deficiency in the mother’s breast milk.[17][18][19][20] To reduce the risk of VKDB, a single 1-milligram (mg) intramuscular injection of vitamin K is routinely administered to newborns.[17][18][19][20] In adults, there is also a relationship between the dietary intake of vitamin K and normal blood coagulation.[21]

    Observational studies have found that insufficient dietary intake of vitamin K (i.e., lower than the adequate intake) and low serum concentrations of vitamin K are associated with low bone mineral density.[22][23][24] It is also generally agreed that there is a relationship between the dietary intake of vitamin K and the maintenance of normal bone health.[21] However, while meta-analyses of randomized controlled trials have found that supplementation with vitamin K can affect markers of bone health, including bone mineral density,[3] the effects on bone fracture risk are inconsistent.[4][5] Further research is needed to determine whether vitamin K can prevent or treat osteoporosis.

    Low serum concentrations of vitamin K have been associated with coronary artery calcium progression, a marker of calcification and stiffening of arteries which can cause cardiovascular disease.[25] Consequently, vitamin K has been suggested to support cardiovascular health. However, while low serum concentrations of vitamin K appear to be associated with a greater cardiovascular disease risk and higher mortality,[26][27][26] the current evidence does not show a relationship between the dietary intake of vitamin K and the normal function of the cardiovascular system or cardiovascular disease mortality.[21][26] Furthermore, meta-analyses of randomized controlled trials do not support a benefit of vitamin K supplementation on cardiovascular health.[28][29][30][31]

    Low serum concentrations of vitamin K have also been associated with a higher risk of type 2 diabetes,[32] but randomized controlled trials show that the effect of supplementation with vitamin K on fasting glucose and insulin resistance is trivial and highly variable.[32][33][34]

    Supplementation with vitamin K might play a role in cancer therapy, but further randomized controlled trials are needed to make firm conclusions.[35]

    Evidence for Vitamin K

    What are vitamin K’s main drawbacks?

    While case studies have shown that injectable forms of vitamin K1 can cause allergic reactions[10][36][37] and that high doses of vitamin K3 can cause hemolytic anemia in some people,[10] the consumption of vitamin K is not associated with adverse effects or toxicity in the general population.[1][10][38][39] That said, vitamin K does interact with some drugs, including blood-thinning drugs (anticoagulants) like warfarin and drugs that affect the intestinal absorption of dietary fat, such as colesevelam and orlistat. People who use such drugs should consult their doctor before considering using a vitamin K supplement or altering their dietary intake of foods rich in vitamin K.

    How does vitamin K work?

    In humans, the main mechanistic role of vitamin K is in the γ-carboxylation of proteins called vitamin-K-dependent proteins. Several vitamin-K-dependent proteins have been identified, and they are primarily involved in the regulation of blood coagulation, vascular function, and bone metabolism.[10][40][11][12]

    Supplementation with vitamin K can improve markers of bone health.[3][4][5] Evidence from animal studies and cell-culture studies shows that vitamin K can promote processes involved in bone formation (e.g., osteoblast differentiation and the carboxylation of osteocalcin), suppress processes involved in bone breakdown (e.g., osteoclast formation), and increase the concentration of enzymes (bone-specific alkaline phosphatase) and growth factors (IGF-1, GDF-15, etc.) involved in bone formation.[41][42][43]

    What are other names for Vitamin K

    Note that Vitamin K is also known as:
    • Phylloquinone (Phytomenadione; vitamin K1)
    • Menaquinone-4 (MK-4
    • Menatetrenone; vitamin K2)
    • Menaquinone-7 (MK-7; vitamin K2)
    • Menadione (sometimes called vitamin K3)
    Vitamin K should not be confused with:
    • Pyrroloquinoline quinone (PQQ)

    Dosage information

    Formulations:

    • Phylloquinone (vitamin K1)
    • Menaquinone-4 and menaquinone-7 (vitamin K2)
    • Menadione (vitamin K3) is rarely used in supplements.

    Range of dosages studied:

    • Phylloquinone (vitamin K1): 0.1–10 mg per day (mg/day), equivalent to 100–10,000 micrograms (μg) per day.
    • Menaquinone-4 (vitamin K2): 1–90 mg/day (1,000–90,000 μg/day).
    • Menaquinone-7 (vitamin K2): 0.09–2 mg/day (90–2,000 μg/day).

    Safety information:

    Vitamin K interacts with several drugs, including blood-thinning (anticoagulant) drugs like warfarin and drugs that affect the intestinal absorption of dietary fat, such as colesevelam and orlistat. Vitamin K absorption and metabolism can be impaired in people with hepatobiliary dysfunction. A tolerable upper intake level (UL) for vitamin K has not been set, because there is insufficient data assessing the risk.[1][2] This does not mean that taking an amount higher than the recommended dose is safe, just that current data does not find adverse effects.

    Dosage recommendation:

    The dosages that have been found to improve markers of bone health are 0.1–5 mg/day (100–5000 μg/day) of phylloquinone (vitamin K1), 15–45 mg/day of menaquinone-4 (vitamin K2), or 100–375 μg/day of menaquinone-7 (vitamin K2).[3][4][5]

    The adequate intake (AI) — the daily intake that ensures nutritional adequacy in most people — in micrograms (µg) per day for vitamin K is shown below.[1][2] Note that the AI for vitamin K varies slightly between countries; the data below are for the US.

    AgeMaleFemalePregnancyLactation
    0–6 months2.0 µg/day2.0 µg/day----
    7–12 months2.5 µg/day2.5 µg/day----
    1–3 years30 µg/day30 µg/day----
    4–8 years55 µg/day55 µg/day----
    9–13 years60 µg/day60 µg/day----
    14–18 years75 µg/day75 µg/day75 µg/day75 µg/day
    Older than 18 years120 µg/day90 µg/day90 µg/day90 µg/day

    Vitamin K is found in several foods. High amounts per serving are found in spinach, broccoli, kale, Brussels sprouts, collards, soybeans, etc.[6][7][8][9] Consult the FoodData Central database to check the amounts of vitamin K in the foods you eat.

    Take with food: Yes. Intestinal absorption of vitamin K appears to be improved in the presence of dietary fat.[10]

    Frequently asked questions

    What is vitamin K?

    Vitamin K is an essential vitamin that plays an important role in blood coagulation, bone metabolism, and vascular health, and it is one of the four fat-soluble vitamins (along with vitamin A, vitamin D, and vitamin E).[10][11][12] Vitamin K is actually the collective term for several fat-soluble molecules called 2-methyl-1,4-naphthoquinones.[10][11][12]

    There are two naturally occurring forms of vitamin K: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). K1 is the major dietary form and is found in several plant-based foods including spinach, broccoli, kale, Brussels sprouts, collards, and soybeans.[6][10][11][12] Vitamin K2 is synthesized by bacteria — including gut bacteria in our microbiome — and is found in meat and fermented foods (e.g., nattō; fermented soybeans).[13][8][10][11][12]

    Phylloquinone (vitamin K1) is the predominant form used in vitamin K supplements, but menaquinones (vitamin K2) are also used.[10][14] Another form of vitamin K called menadione (or vitamin K3) is an intermediate molecule in vitamin K metabolism.[10][12][15] It is not typically used in human supplements, but it is used in animal feed.[16]

    What are the signs and symptoms of vitamin K deficiency?

    The symptoms of vitamin K deficiency include bleeding disorders, impaired bone development, and spontaneous rash.[10][44] The signs of vitamin K deficiency include biomarkers of vitamin K status, such as low serum concentrations of phylloquinone (vitamin K1) and PIVKA-II (protein induced by vitamin K absence or antagonist-II).[45][44] PIVKA-II is an incompletely carboxylated form of prothrombin, which is a key protein involved in blood coagulation that is carboxylated by vitamin K.[45][44]

    What causes vitamin K deficiency?

    In newborn babies, a vitamin K deficiency can arise due to inadequate vitamin K storage or a vitamin K deficiency in the mother’s breast milk.[17][18][19][20] This can lead to a type of hemorrhage called vitamin K deficiency bleeding.

    Vitamin K deficiency is not common in adults. Still, it can occur due to inadequate dietary intake or the use of drugs known to interfere with the absorption, metabolism, and synthesis of vitamin K (e.g., anticoagulants and drugs that affect the intestinal absorption of dietary fat).[10] It is also possible that antibiotics can inhibit the growth of vitamin-K-producing bacteria in the intestine and increase the risk of vitamin K deficiency.[10]

    Vitamin K deficiency can also occur in people with hepatobiliary dysfunction or inflammatory bowel disease due to the impaired absorption and metabolism of vitamin K.

    In women, severe nausea and vomiting during pregnancy (known as hyperemesis gravidarum) and malnutrition during pregnancy can also cause vitamin K deficiency and lead to hemorrhage.[10][46][47]

    What are vitamin K’s main benefits?

    Due to vitamin K’s role in blood coagulation, bone metabolism, and vascular health,[10][11][12] supplementation with vitamin K is claimed to have a range of benefits on blood clotting (coagulation), bone health, cardiovascular health, diabetes and blood sugar, and cancer.

    The main benefit of vitamin K supplementation is in newborn babies, because vitamin K deficiency bleeding (VKDB) can arise due to inadequate vitamin K storage or a vitamin K deficiency in the mother’s breast milk.[17][18][19][20] To reduce the risk of VKDB, a single 1-milligram (mg) intramuscular injection of vitamin K is routinely administered to newborns.[17][18][19][20] In adults, there is also a relationship between the dietary intake of vitamin K and normal blood coagulation.[21]

    Observational studies have found that insufficient dietary intake of vitamin K (i.e., lower than the adequate intake) and low serum concentrations of vitamin K are associated with low bone mineral density.[22][23][24] It is also generally agreed that there is a relationship between the dietary intake of vitamin K and the maintenance of normal bone health.[21] However, while meta-analyses of randomized controlled trials have found that supplementation with vitamin K can affect markers of bone health, including bone mineral density,[3] the effects on bone fracture risk are inconsistent.[4][5] Further research is needed to determine whether vitamin K can prevent or treat osteoporosis.

    Low serum concentrations of vitamin K have been associated with coronary artery calcium progression, a marker of calcification and stiffening of arteries which can cause cardiovascular disease.[25] Consequently, vitamin K has been suggested to support cardiovascular health. However, while low serum concentrations of vitamin K appear to be associated with a greater cardiovascular disease risk and higher mortality,[26][27][26] the current evidence does not show a relationship between the dietary intake of vitamin K and the normal function of the cardiovascular system or cardiovascular disease mortality.[21][26] Furthermore, meta-analyses of randomized controlled trials do not support a benefit of vitamin K supplementation on cardiovascular health.[28][29][30][31]

    Low serum concentrations of vitamin K have also been associated with a higher risk of type 2 diabetes,[32] but randomized controlled trials show that the effect of supplementation with vitamin K on fasting glucose and insulin resistance is trivial and highly variable.[32][33][34]

    Supplementation with vitamin K might play a role in cancer therapy, but further randomized controlled trials are needed to make firm conclusions.[35]

    Evidence for Vitamin K

    What are vitamin K’s main drawbacks?

    While case studies have shown that injectable forms of vitamin K1 can cause allergic reactions[10][36][37] and that high doses of vitamin K3 can cause hemolytic anemia in some people,[10] the consumption of vitamin K is not associated with adverse effects or toxicity in the general population.[1][10][38][39] That said, vitamin K does interact with some drugs, including blood-thinning drugs (anticoagulants) like warfarin and drugs that affect the intestinal absorption of dietary fat, such as colesevelam and orlistat. People who use such drugs should consult their doctor before considering using a vitamin K supplement or altering their dietary intake of foods rich in vitamin K.

    How does vitamin K work?

    In humans, the main mechanistic role of vitamin K is in the γ-carboxylation of proteins called vitamin-K-dependent proteins. Several vitamin-K-dependent proteins have been identified, and they are primarily involved in the regulation of blood coagulation, vascular function, and bone metabolism.[10][40][11][12]

    Supplementation with vitamin K can improve markers of bone health.[3][4][5] Evidence from animal studies and cell-culture studies shows that vitamin K can promote processes involved in bone formation (e.g., osteoblast differentiation and the carboxylation of osteocalcin), suppress processes involved in bone breakdown (e.g., osteoclast formation), and increase the concentration of enzymes (bone-specific alkaline phosphatase) and growth factors (IGF-1, GDF-15, etc.) involved in bone formation.[41][42][43]

    Other FAQs
    Should you supplement with vitamin K?
    Quick answer:

    Research is still scarce, but current evidence suggests that, through their effect on calcium regulation, some forms of vitamin K can help prevent osteoporosis and cardiovascular diseases.

    Vitamin K is poorly understood, both by the general public and among health professionals. It has a wide range of potential benefits, but their nature and extent are still uncertain.

    Why is that?

    Some vitamins are more popular than others. In the past, a lot of research went into vitamin C, which became a popular supplement. Nowadays, a lot of research goes into vitamin D, whose popularity as a supplement is steadily growing.

    By contrast, research on vitamin K is still scarce, having slowly developed over the past two decades. Further, it is scattered, because there exist several forms of vitamin K. Some of those forms are present only in a few foods. Others exist in various foods, but only in minute amounts. Few have been the subject of human trials.

    The human trials that do exist, however, are overall promising. In order to understand their value and limitations, first you need to know a few basic facts. So let’s begin:

    What is vitamin K?

    Of the four fat-soluble vitamins (A, D, E, and K), vitamin K was discovered last. In 1929, Danish scientist Henrik Dam discovered a compound that played a role in coagulation (blood clotting).[48] When he first published his findings, in a German journal, he called this compound Koagulationsvitamin, which became known as vitamin K.

    Today, we know that vitamin K participates in some very important biological processes, notably the carboxylation of calcium-binding proteins (including osteocalcin and matrix GLA protein).[49] In other words, vitamin K helps modify proteins so they can bind calcium ions (Ca2+). Through this mechanism, vitamin K partakes in blood clotting, as Henrik Dam discovered, but also of calcium regulation: it helps ensure that more calcium gets deposited in bones and less in soft tissues, thus strengthening bones and reducing arterial stiffness.

    What complicates matters is that each vitamin has different forms, called vitamers, each of which may affect you differently. Vitamin K has natural vitamers, K1 (phylloquinone) and K2 (menaquinone), and synthetic vitamers, the best-known of which is K3 (menadione).

    Vitamin K1

    K1 is produced in plants, where it is involved in photosynthesis: the greener the plant, the greater its chlorophyll content; the greater its chlorophyll content, the greater its K1 content. When it comes to foods, K1 is especially abundant in green leafy vegetables.

    K1 makes for 75–90% of the vitamin K in the Western diet.[15] Unfortunately, K1 is tightly bound to chloroplasts (organelles that contain chlorophyll and conduct photosynthesis), so you could be absorbing very little of what you eat[50] — maybe less than 10%.[51] Since vitamin K is a fat-soluble vitamin, however, its absorption can be enhanced by the co-ingestion of fat: adding fat to cooked spinach can raise K1 bioavailability from 5% to 13%.[52]

    Vitamin K2

    Things become more complicated here, because just as there are several forms of vitamin K, there are several forms of vitamin K2. To be more precise, the side chain of K1 always has four isoprenoid units (five-carbon structures), so there is only one form of K1, but the side chain of K2 has n isoprenoid units, so there are n forms of K2, called MK-n.[53][54]

    image

    Whereas the side chain of K1 has four saturated isoprenoid units, the side chain of K2 MK-4 has four unsaturated isoprenoid units. Although K1 is directly active in your system, your body can also convert it to MK-4.[11][55][56] How much gets converted depends notably on your genetic heritage.[15]

    MK-4 is present in animal products (meat, eggs, and dairy), though only in small quantities. Because those foods usually contain fat, dietary MK-4 should be better absorbed than dietary K1,[57] but future studies will need to confirm this hypothesis.

    image

    Other than MK-4, all forms of K2 are produced by bacteria. Your microbiota was once thought to produce three-fourths of the vitamin K you absorb.[58] Vitamin K, however, is mostly produced in the colon, where there are no bile salts to facilitate its absorption, so the actual ratio is probably much lower.[57][59]

    Bacteria-produced K2 can be found in fermented foods, such as cheese and curds, but also in liver meat.[60] The richest dietary source of K2 is natto (fermented soybeans), which contains mostly MK-7.[61][62] As it stands, MK-7 is the only form of K2 that can be consumed in supplemental doses through food (i.e., natto). For that reason, MK-7 is the most-studied form of K2, together with MK-4.

    K1 and MK-4 both have a side chain composed of four isoprenoid units; their half-life in your blood is 60–90 minutes. MK-7 has a side chain composed of seven isoprenoid units; it remains in your blood for several days. Due to their different side-chain lengths, the various forms tend to be transported on different lipoproteins, which are taken up at different rates by various tissues.[63][64][65][66][67] K1 and MK-4 are used quickly (K1 in the liver, MK-4 in other specific tissues), whereas MK-7 has more time to travel and be used throughout the body (which makes it, in theory, the best option for bone health).

    Vitamin K3

    K1 and K2 are the only natural forms of vitamin K, but there exist several synthetic forms, the best known of which is K3. However, whereas the natural forms of vitamin K are safe, even in high doses, K3 can interfere with glutathione, your body’s main antioxidant. K3 was once used to treat vitamin K deficiency in infants, but it caused liver toxicity, jaundice, and hemolytic anemia. Nowadays, it is used only in animal feed, in small doses. In the animals, vitamin K3 gets converted into K2 MK-4,[68] which you can consume safely.

    Vitamin K is a family of fat-soluble vitamins. K1 and K2, the natural forms, are safe even in high doses. There is only one type of K1; it is found in plants, notably green leafy vegetables; your body can use it directly or convert it to K2 MK-4. Aside from MK-4, all other types of K2 are produced by bacteria, including the bacteria populating your gut. MK-4 is present in animal products (meat, eggs, dairy), whereas other types of K2 can be found in fermented foods and liver meat.

    Vitamin K and your health

    As far as we know, vitamin K mainly affects bloodclotting, cardiovascular health, and bone health. Epidemiological studies have mostly focused on K1; cardiovascular trials, on K1 and MK-7 (the main type present in natto, the richest dietary source of K2); bone trials, on MK-4 (the type of K2 your body can make out of K1).

    Blood clotting

    Vitamin K deficiency impairs blood clotting, causing excessive bleeding and bruising. It is rare in adults, but more common in newborns (more than 4 cases per 100,000 births in the UK[69]), where it can result in life-threatening bleeding within the skull. For that reason, the American Academy of Pediatrics recommends that newborns receive K1 shortly after birth (intramuscular injections have shown greater efficacy than oral administration).[70]

    If you suffer from hypercoagulation (if your blood clots too easily), you might be prescribed a vitamin K antagonist (VKA), such as warfarin, a medication that hinders the recycling of vitamin K. Some doctors recommend that VKA users shun vitamin K entirely, but preliminary evidence suggests that, under professional supervision, vitamin K supplements might help stabilize the effects of VKAs.[60]

    Which form should be supplemented, though, and in what amount, is still uncertain. There is some evidence that K1 enhances coagulation more than does MK-4[71][72] but less than does MK-7.[65] With regard to daily supplementation, 100 μg of K1 is considered safe, but in some people 10 μg of MK-7 is enough to significantly impair VKA therapy.[73]

    Remember that natto is rich in MK-7. A single serving of natto can increase blood clotting for up to four days,[74] so it is one food VKA users should avoid. Other foods should be safe to eat. Please note that in people who do not suffer from hypercoagulation, and thus do not need to medicate with VKA, high intakes of natto have never been correlated to excessive blood clotting. Similarly, human studies saw no increase in blood-clot risk even from 45 mg (45,000 μg) of MK-4 taken once[75] or even thrice[76] daily.

    Cardiovascular health

    As we saw, vitamin K partakes in calcium regulation: it helps ensure that more calcium gets deposited in bones and less in soft tissues, thus reducing arterial stiffness. This is why people who take vitamin K antagonists, such as warfarin, are more likely to suffer from vascular calcification.[77][78]

    Epidemiological studies[79][80][81] and mechanistic evidence[82] suggest that dietary K2 benefits cardiovascular health more than an equal dose of dietary K1.

    Clinical trials on supplemental vitamin K have focused on K1[83][84] and MK-7.[85][86][87] Often, those trials used a combination of vitamin D and other nutrients, but with vitamin K being the key difference between the intervention group and the control groups. Both of these forms of vitamin K seem to cause a consistent reduction in arterial stiffness (with better evidence for MK-7), and less consistent reductions in coronary calcification and carotid intima-media thickness. Judging from those trials and the epidemiological evidence, MK-7 seems the better choice.

    Bone health

    As we have just seen again, vitamin K partakes in calcium regulation: it helps ensure that less calcium gets deposited in soft tissues and more in bones, thus strengthening the latter. This is why people who take vitamin K antagonists, such as warfarin, might be more at risk of bone fractures,[88][89] though not all studies agree they are.[90]

    Current evidence suggests that supplementing with vitamin K — or, at least, with certain forms of vitamin K — can benefit bone health, especially in the elderly (who have lower levels of circulating K2).[91] This potential should be explored, since, as the world population grows (and grows older), so does the number of osteoporotic fractures.[92] [93][94]

    MK-7 appears to support the carboxylation of osteocalcin (a major calcium-binding protein in bones) more efficiently than K1.[65] Clinical trials suggest that, for the purpose of increasing bone density, MK-4 and MK-7 work more reliably than K1.[3]

    More significantly, a meta-analysis of MK-4 trials found an overall decrease in fracture risk.[95] The effect of K1 or MK-7 supplementation on fracture risk is less clear. Only one K1 trial looked at fracture risk; it reported a decrease, but without a concomitant increase in bone mineral density.[96] Of the two MK-7 trials, one reported no difference in the number of fractures between the placebo group and the MK-7 group,[97] whereas the other reported fewer fractures in the MK-7 group;[98] there were, however, no statistical analyses for either study.

    More research on vitamin K and fracture risk will be needed to clarify the effects of the different forms at different dosages. Currently, if you wish to supplement for bone health, a very high dose of MK-4 (45,000 μg) is the option best supported by human studies.[95] Those studies, all in Japanese people, focused on the prevention of bone fractures, and yes, much smaller dosages can probably help support bone health; but how much smaller?

    In a 12-month study, 20 patients suffering from a chronic kidney disorder were given a daily glucocorticoid (a corticosteroid that has for side effect to decrease bone formation and increase bone resorption). In addition, half the patients received 15 mg of MK-4 daily, while the other half received a placebo. The placebo group experienced bone-density loss (BDL) in the lumbar spine, while the MK-4 group did not.[99]

    More recently, a 12-month study in 48 postmenopausal Japanese women gave 1.5 mg of MK-4 daily to half of them and found a significant reduction in forearm BDL, but not in hip BDL, and it didn’t evaluate fractures.[100]

    So there is some evidence for dosages lower than 45 mg/day. It is, however, a lot weaker.

    In healthy people, vitamin K supplementation does not increase the risk of blood clots. Judging from limited evidence, MK-7 seems to be the best form of vitamin K for cardiovascular health, and MK-4 the best form of vitamin K for bone health.

    How much vitamin K do you need?

    Since vitamin K is crucial to your health, why is it the subject of relatively few studies? One of the reasons is simply that vitamin K deficiency is very rare in healthy, well-fed adults. It is mostly a concern in newborns, in people who have been prescribed a vitamin K antagonist, in people who suffer from severe liver damage, and in people who have problems absorbing fat.[101][102][103]

    Vitamin K is abundant in a balanced diet, and the bacteria in your colon can also produce some. Moreover, your body can recycle it many times, and this vitamin K-epoxide cycle more than makes up for the limited ability your body shows for storing vitamin K.

    Still, you can recycle vitamin K many times, but not forever, and so you still need to consume some regularly. But how much, exactly?

    No one knows. There is, as yet, not enough evidence to set a Recommended Dietary Allowance (RDA) for vitamin K, so an Adequate Intake (AI) has been established at a level assumed to prevent excessive bleeding. In the United States, the AI for vitamin K is 120 μg/day for men and 90 μg/day for women. In Europe, the AI for vitamin K is 70 μg/day for men and women. More recent research, however, suggests that those numbers should be increased.[64]

    Since 100 g of collards contain, on average, 360 μg of vitamin K,[104][53] getting enough vitamin K looks easy. But can’t you just as easily get too much?

    Fortunately, no. Though allergic reactions have occurred with vitamin K injections,[105][106][107] no incidence of actual toxicity has ever been reported in people taking natural vitamin K, even in high supplemental doses.[1] For that reason, neither the FDA nor the EFSA has set a Tolerable Upper Intake Level (UL) for vitamin K. One should note, however, that we lack long-term, high-dose studies on vitamin K safety.

    Sources of vitamin K

    K1 can be found in plant products, notably green leafy vegetables. K2 MK-4 can be found in animal products (meat, eggs, and dairy). The other types of K2 can be found in fermented foods and liver meat.

    image

    Table references: [108][109][53][110][111][67][104][112][113]

    Meats’ vitamin K content correlates positively but non-linearly with their fat content and will vary according to the animal’s diet (and thus country of origin). Forms of K2 other than MK-4 and MK-7 have not been well studied but are likely to have some benefit — cheeses and beef liver are notable sources of others forms of K2[109][113] and cheese consumption is associated with a reduced risk of cardiovascular disease.[114]

    While well-conducted controlled trials provide the most reliable evidence, most such trials used amounts of vitamin K2 that far exceed what could be obtained through foods, save for natto. This leaves us wondering if dietary K2 has any effect.

    Fortunately, it seems to be the case: a high dietary intake of K2 (≥33 μg/day seems optimal) may reduce the risk of coronary heart disease — an effect a high dietary intake of K1 doesn’t appear to have.[79][81][80][115] It doesn’t mean, of course, that foods rich in K1 are valueless: dietary K1 intake will protect you from excessive bleeding and is inversely associated with risk of bone fractures.[116]

    Observational studies, however, are less reliable than controlled trials, so we know less about the effects of dietary intake than about the effects of supplemental intake. If you wish to supplement with vitamin K, here are the dosages supported by the current evidence:

    image

    Summary

    Although much more research needs to be performed, there is early evidence that vitamin K, whether in food or in supplemental form, can benefit cardiovascular health and bone health.


    image

    Update History

    References

    1. ^Institute of Medicine (US) Panel on MicronutrientsDietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
    2. ^EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), Turck D, Bresson JL, Burlingame B, Dean T, Fairweather-Tait S, Heinonen M, Hirsch-Ernst KI, Mangelsdorf I, McArdle HJ, Naska A, Nowicka G, Pentieva K, Sanz Y, Siani A, Sjödin A, Stern M, Tomé D, Van Loveren H, Vinceti M, Willatts P, Lamberg-Allardt C, Przyrembel H, Tetens I, Dumas C, Fabiani L, Ioannidou S, Neuhäuser-Berthold MDietary reference values for vitamin K.EFSA J.(2017 May)
    3. ^Fang Y, Hu C, Tao X, Wan Y, Tao FEffect of vitamin K on bone mineral density: a meta-analysis of randomized controlled trialsJ Bone Miner Metab.(2012 Jan)
    4. ^Mott A, Bradley T, Wright K, Cockayne ES, Shearer MJ, Adamson J, Lanham-New SA, Torgerson DJEffect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials.Osteoporos Int.(2019-Aug)
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