ビタミンK
The classic role of vitamin K is to maintain the body’s normal coagulation function, so it is also called a coagulation vitamin. The most important vitamin K is vitamin K₁ and K₂, so it is generally classified as a fat-soluble vitamin in its natural form, but some synthetic forms are water-soluble vitamins.
Natural forms of vitamin K include K₁ (phylloquinones) and K₂ (menaquinones), which are fat-soluble and stable to heat, but are susceptible to damage by acids, alkalis, oxidants and light (especially ultraviolet rays). Only a small amount is lost during the cooking process. However, artificially synthesized vitamins K₃ and K₄ are water-soluble, and artificially synthesized vitamins K₅, K₇, etc. are also available.
Vitamin K₁ mainly exists in natural green foods, which can be obtained from spinach, alfalfa or other plants. Some vegetable oils, such as soybean oil, rapeseed oil, cottonseed oil, etc. are also important sources.
Vitamin K₂ can be synthesized by intestinal bacteria or obtained from fermented beans, meat, eggs, and milk. Although the amount synthesized by intestinal flora is not low, the amount absorbed is very small.
Absorption metabolism
The absorption of vitamins K₁ and K₂, like other fat-soluble vitamins, requires the participation of bile and pancreatic juice, and is combined with chylomicrons and transported by the lymphatic system. The absorption efficiency varies widely (10% to 80%), depending on the source of vitamin K and the excipients of vitamin K taken.
Vitamin K in meals is mostly a mixture of K₁ and K₂. The absorption rate of these mixtures is generally about 40% to 70%. Their absorption mechanisms are different. Both the body itself and intestinal flora can convert vitamin K₁ into vitamin K₂.
The liver’s storage capacity of vitamin K is limited, so the human body stores less vitamin K and renews it quickly, about once every 2.5 hours. The liver stores 10% of the body’s vitamin K₁ and 90% of its vitamin K₂. Within cells, vitamin K is mainly found on biological membranes (especially endoplasmic reticulum and mitochondrial membranes).
The storage capacity of vitamin K is very low, but it can be recycled. Depending on the vitamin K intake, vitamin K can be recycled 200 to 2,000 times a day to maintain the balance of vitamin K in the body。
relationship with health
1. Regulate coagulation protein synthesis
Currently, there are at least 12 proteins in which vitamin K can add a carboxyl group (—COOH) to its specific glutamic acid residue to carboxylate it to Gla. Such proteins are called vitamin K-dependent proteins.
Among them, the classic ones are coagulation factors II, VII, IX and X, which play an important role in preventing bleeding and causing thrombosis. In addition, anticoagulant proteins C and S, and proteins Z and M are also vitamin K-dependent coagulation factors.
2. Promote bone health
Vitamin K₂ can not only promote bone formation and bone mineralization, but also inhibit bone resorption, and has a synergistic effect with drugs commonly used to treat osteoporosis.
In the past, we always emphasized calcium supplementation to treat or prevent osteoporosis, but symptoms of osteoporosis are still not uncommon under high calcium intake, and long-term calcium supplementation (1000 mg/d) is associated with stroke, cardiovascular sclerosis, and large areas of myocardium. Infarction and other diseases are closely related, so the concept of blindly emphasizing calcium supplementation to prevent and treat osteoporosis should be revised.
The key factor to balance the two is vitamin K₂, which can ensure that calcium supplementation plays a positive role while avoiding the side effects of high calcium, because a sufficient amount of vitamin K₂ in plasma can inhibit and reverse abnormal tissue calcification, which means that vitamin K₂ can Let the calcium deposit where it belongs.
Because vitamin K₂ activates osteocalcin to promote bone formation, it also activates γ-carboxylated glutamic acid residue protein (MGP). MGP has important functions such as preventing soft tissue mineralization, regulating cartilage metabolism, and inhibiting cartilage mineralization. , this exquisite calcium-regulating mechanism brings calcium in the human body to the correct tissues and organs, thereby solving the problems of osteoporosis and arterial calcification at the same time.
3. Affect sugar metabolism
Vitamin K can affect insulin resistance and glucose metabolism by mediating changes in osteocalcin (OC), growth inhibitory factor 6, carboxyglutamic acid protein (MGP), adiponectin, inflammatory factors and lipids, so it may be beneficial Prevention and intervention of diabetes.
4.Others
ビタミンK also prevents and reverses cardiovascular calcification, prevents liver cancer and cirrhosis, prevents Alzheimer’s disease, fights cancer (pancreatic cancer, liver cancer, etc.), fights rheumatoid arthritis, prevents varicose veins, promotes human skin health, and treats primary diseases. It plays a role in dysmenorrhea and other aspects.
Deficiency and excess
Lack of
The daily requirement of vitamin K is approximately 1 μg/kg body weight. Vitamin K deficiency mainly causes hypoprothrombinemia, manifested by coagulation defects and bleeding. However, vitamin K deficiency is not common in healthy adults because vitamin K is widely distributed in plant and animal tissues; and normal intestinal flora can synthesize vitamin K₂, and the vitamin K cycle also preserves vitamin K.
high risk groups
• Diet
• Frequent nosebleeds
• Severe burns or trauma, surgery
• Antibiotic treatment, intestinal flora imbalance
• Biliary obstruction, malabsorption, or parenchymal liver disease
• Taking certain medications (including anticonvulsants, coumarins, anticoagulants, certain antibiotics, especially cephalosporins, salicylates, and high doses of vitamin A or vitamin E).
• Patients with pancreatic disease, patients with bile duct disease and small intestinal mucosal atrophy or fatty stools.
Newborns are a high-risk group for vitamin K deficiency, especially premature infants, because: ① The placenta is relatively deficient in transporting lipids; ② The synthesis of prothrombin by the neonatal liver is immature; ③ The content of vitamin K in breast milk is low, only 1~ 2μg/L (milk contains 5-10μg/L); ④ The intestines of newborns are sterile in the first few days after birth. Therefore, many babies are susceptible to hemorrhagic disease of the newborn (HDN).
The consequences of neonatal deficiency are very serious. It usually occurs 1 to 7 days after delivery. It can manifest as bleeding in the skin, gastrointestinal tract, and chest cavity. In the most serious cases, intracranial hemorrhage may occur. Therefore, newborns are currently given vitamin K to prevent deficiency.
primary source
Vitamin K in humans is produced by intestinal flora and supplied by food.
Foods rich in vitamin K include beans, wheat bran, green vegetables, animal liver, fish, etc. Among common green vegetables, kale, cucumber, spinach, etc. have the highest content, followed by leafy vegetables and wild vegetables.
The average vitamin K₁ content of leafy vegetables is 226.3μg/100g, and that of wild vegetables is 341.6μg/100g. However, the content of tender stems, fruits, and root vegetables is lower; the content of vitamin K₁ in vegetable leaves is higher than that in stems. , and the darker the green color of the leaves, the higher the vitamin K₁ content.
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参考文献
[1] Chinese Nutrition Society. Reference intake of dietary nutrients for Chinese residents. Beijing: Science Press, 2014. [2]Suttie JW . The Importance of Menaquinones in Human Nutrition[J]. Annual Review of Nutrition, 1995, 15(1):399-417.[3]Bjrnebye VIKA . Vitamin K2 and arterial calcification[J]. Agro Food Industry Hi Tech, 2008, 19(6):9-13.[4]A, Joline WJ Beulens, et al. “High dietary menaquinone intake is associated with reduced coronary calcification.” Atherosclerosis 203. 2(2009):489- 493.[5]Ren Ruijun, Tan Jing. Research progress on vitamin K and glucose metabolism[J]. Chinese General Medicine, 2019, 22(29):5.[6] Kaneki, M., et al. “Pleiotropic actions of Vitamin K: protector of bone health and beyond?.” Nutrition 22.7-8(2006):845-852.
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