With the rapid development of medicine, trace element iron plays an important role in human health, especially in the growth and development of infants. If there is iron deficiency in the body, it will not only cause iron deficiency anemia, but also affect intellectual development. Excessive iron supplementation will be harmful to human body. Like other trace elements, iron has a certain content and proportion in human body. If you give your child iron supplements indiscriminately, it will have adverse consequences, such as affecting the absorption of zinc and causing zinc deficiency; After excessive absorption, iron reaches the heart, liver, lung and other important organs through blood circulation, and is deposited in these organs, causing a serious disease, namely hemochromatosis. It can be seen that children can neither take too much iron-containing preparations nor eat too much iron-fortified foods. They should always eat any kind of food containing more iron, such as fungus, kelp, pork liver, meat, beans, eggs, etc., so as not to be short of iron. Children with iron deficiency diagnosed by hair and blood tests should also take iron-containing drugs under the specific guidance of doctors. In recent years, with the improvement of living standards, people's health awareness has gradually increased, but due to the lack of correct nutrition knowledge, the prevalence of various nutrition-related diseases has risen sharply. According to the Survey on Nutrition and Health Status of Residents in China issued by the Ministry of Health on June 5438+ 10, 2004, the lack of micronutrients such as iron and vitamin A is a common problem among urban and rural residents in China. The average prevalence rate of anemia among residents in China is 15.2%. The prevalence rates of anemia in infants under 2 years old, elderly people over 60 years old and women of childbearing age were 24.2%, 265,438+0.5% and 20.6% respectively [65,438+0]. At present, about 20% ~ 50% of people in the world suffer from iron deficiency to varying degrees, especially in developing countries, and the incidence rate is about four times that of developed countries. It can be seen that iron deficiency anemia has become the public health problem with the highest prevalence rate and the highest cost in the world after tuberculosis [2]. Therefore, it is of great significance to help people master the relevant nutrition knowledge and understand the metabolism and physiological function of iron in human body, so as to improve people's iron deficiency and improve their physique.
The content and distribution of 1 iron in human body
Iron is one of the essential trace elements in human body, accounting for 0.006% of human body weight, that is, adults contain about 4.0g of iron, of which 70% of iron exists in hemoglobin, myoglobin, hemease, cofactor and carrier iron, also called functional iron; The remaining 30% iron is stored in the body, mainly in the form of ferritin and hemosiderin in the liver, spleen and bone marrow. Iron is widely distributed in human body, almost in all tissues, with the highest content in liver and spleen, followed by kidney, heart, skeletal muscle and brain [3]. The iron content in the body varies greatly with age, sex, nutritional status and health status. In addition, in infectious diseases and malignant lesions, the iron content in the liver can be greatly increased [4].
2 Absorption and excretion of iron
2. 1 iron absorption
Iron is mainly absorbed in duodenum and upper jejunum. Fe2+ is oxidized to Fe3+ under the action of ceruloplasmin, which is then combined with transferrin and transported to various tissues. In tissues and cells, Fe3+ is separated from transferrin and reduced to Fe2+. Plasma transferrin transports most iron to bone marrow for Hb synthesis, and a small part to tissues and cells for iron protein synthesis or storage [5].
Iron in food is generally divided into two categories: heme iron and non-heme iron. Heme iron mainly comes from animal food, which can combine with protoporphyrin in hemoglobin and myoglobin, and is not affected by phytate and oxalate, and is directly absorbed by intestinal mucosal epithelial cells. Therefore, the absorption rate of heme iron is high, and it is not interfered by the influencing factors of iron absorption in intestinal cavity. Non-heme iron mainly comes from plant food. Before absorption, it must be separated from the bound organic matter and converted into soluble divalent ions in order to be easily absorbed. Therefore, the absorption of non-heme iron is largely influenced by dietary factors, mainly in the following aspects:
The first is iron intake. Under normal circumstances, the human body's intake of iron increases, so does its absorption. Although the percentage absorbed is very low when ingested in large quantities, the absolute amount absorbed has increased. Among them, ferrous iron is more easily absorbed than ferric iron.
The second is the influence of physical condition on iron absorption: ① gastrointestinal factors. Acidic gastric juice helps to maintain the solubility and reducibility of iron, so insufficient gastric acid in the body or taking antacids will affect the absorption of iron. ② Hematopoiety and iron storage. Many studies have proved that iron absorption is related to iron demand and storage in the body. Generally speaking, when the storage capacity is long, the absorption rate is low; conversely, when the storage capacity is low or the demand increases, the absorption rate increases. ③ Growth, development and age. The iron absorption rate increases obviously with the decrease of iron storage in infancy, but decreases gradually with the increase of age after entering the middle-aged and elderly stage.
The third is the dietary factor. Food collocation is one of the important factors affecting iron absorption. Non-heme iron in the diet must be converted into ferrous iron to be absorbed. Dietary fiber, polyphenols, phytate and oxalate in plant food affect its absorption. In addition, vitamin A, vitamin C, vitamin B2, beta-carotene, organic acids, animal foods and some monosaccharides and lipids can promote the absorption of iron.
2.2 Iron excretion
The body's ability to excrete iron is limited, mainly in three forms: first, it is excreted by epithelial cells of digestive tract, such as bile, exfoliated mucosal cells and a small amount of blood through feces; Second, it is excreted through sweat and skin exfoliated cells; The third reason is urine excretion. Adults excrete about 0.90 ~ 1.05 mg of iron every day, 90% of which is excreted from the intestine, with little urine. In addition, menstruation and bleeding are also ways of iron excretion.
3 Physiological function of iron
Iron has high biological activity, and participates in the synthesis of hemoglobin, myoglobin, cytochrome, cytochrome oxidase, peroxidase and catalase, which is related to the activities of acetyl-CoA, succinate dehydrogenase, xanthine oxidase and cytochrome reductase. When there are more than 1/2 enzymes and factors in the iron-containing or iron-containing tricarboxylic acid cycle, it can play a biochemical role and complete its physiological function [6].
3. 1 Participate in the transport and exchange of oxygen in the body and the process of tissue respiration.
One is to synthesize hemoglobin. Red blood cells are the truncated bodies of oxygen, and hemoglobin is an important part of them. Hemoglobin consists of two parts, one of which is an iron-containing substance called heme, which is a complex of Fe2+. In its molecule, four porphyrin rings surround the iron atom in the middle, and the divalent iron atom is like the "spider" in the center of the spider web [7]. Therefore, it can reversibly combine with oxygen, so that hemoglobin has the function of carrying oxygen and participates in the transportation and exchange of CO2 in the body and tissue respiration.
The second is to synthesize myoglobin. Myoglobin is a kind of protein containing heme, which is composed of heme and globulin. The basic function of myoglobin is to transport and store oxygen in muscle tissue. Iron plays an indispensable role in myoglobin synthesis.
The third is to form cytochrome and some respiratory enzymes. Cytochrome is also a compound containing heme, which has electron transfer function in mitochondria and is also a component of various respiratory enzymes. Iron is an important component of cytochrome.
3.2 Maintain normal hematopoietic function
The importance of iron to human health lies in that it is an essential part of hemoglobin and one of the essential elements in hematopoiesis. Erythropoiesis requires not only the normal hematopoietic function of bone marrow, but also enough hematopoietic raw materials. The main raw materials for making red blood cells are protein and ferrous iron. Iron in red blood cells accounts for about 2/3 of the total iron in the body. Iron combines with porphyrin in bone marrow hematopoietic cells to form heme, and then combines with globin to synthesize hemoglobin.
3.3 Enhance immune function
Iron can keep T lymphocytes, serum complement activity, phagocytosis and bactericidal ability of neutrophils normal. It is found that iron deficiency can reduce lymphocytes and reduce the activity of natural killer cells. In addition, iron can catalyze the transformation of β -carotene into vitamin A, the synthesis of purine and collagen, the production of antibodies, the transport of lipids in blood and the detoxification of drugs in liver.