There are dozens of chemical elements in human body. Except for carbon, hydrogen, oxygen and nitrogen, which mainly exist in the form of organic compounds, all other elements exist in the form of inorganic salts or minerals. Some of these minerals are necessary to maintain normal physiological functions of the human body, so they must be continuously supplied from the diet. These 1 1 elements, such as oxygen, carbon, hydrogen, ammonia, calcium, phosphorus, potassium, sulfur, sodium, magnesium, chlorine, etc., are abundant in the body and are called essential macro elements for human body, accounting for about 60% ~ 80% of the total composition (mass fraction) of human body. These macroelements are mainly supplemented from protein, fat, sugar, inorganic salts, vitamins, water and other substances to meet the needs of human metabolism. Other elements are very few in the body, and some even have trace amounts (the content is μ g/kg). Generally, the elements with the body content less than 0. 1g/kg are called trace elements. At present, it is known that the trace elements necessary for human body are iron, zinc, iodine, copper, selenium, fluorine, molybdenum, cobalt, chromium, nickel, barium and silicon 14. Trace elements exist in blood, liver, spleen, bones, muscles, brain, pancreas, thyroid, adrenal gland, retina, islet tissue, prostate, heart, teeth, nails and lungs. The effects of trace elements on human physiological functions mainly include: ① promoting the catalysis of enzymes; Participate in hormone secretion activities, such as thyroid and adrenal gland secretion activities; ③ is the composition of genetic material nucleic acid; ④ Participating in metabolism-the activity of redox system in human body. Trace elements mainly come from food, drinking water, air and medicine, and biological trace elements are more important than vitamins in human nutrition.
There is a certain correlation between the average abundance of various elements in human body and the average abundance in crustal rocks. Except for carbon, hydrogen, oxygen, nitrogen and silicon in the earth's crust, the contents of other chemical elements in human blood are strikingly similar to those in the earth's crust, which shows that the chemical composition of human body is related to the evolution of the earth's crust. The chemical composition in modern human body is the result of long-term absorption and exchange of elements in the natural environment, continuous evolution, inheritance and variation. The path of trace elements entering the human body in nature is shown in Figure 93.
Fig. 9-3 Schematic diagram of trace elements entering human body in nature (according to Kara W M, 1997)
Some trace elements ingested by the human body are necessary for the human body. Without these elements, people cannot survive or keep healthy, such as fluorine, zinc, cobalt, bromine, copper, barium, selenium, manganese, iodine, nickel, molybdenum and chromium. Some elements are toxic to human body, such as arsenic, cadmium, mercury, lead, antimony, thallium and rare earth metals. The human body's demand for various trace elements depends on age, physiological conditions, environmental conditions and genetic factors. According to the World Health Organization, the demand of adults for certain essential trace elements is shown in Table 9- 12.
Table 9- 12 Requirements of Essential Trace Elements for Adults
Although there are few trace elements in human body, they play a key role in biochemical process and maintain the metabolic process of life. Table 9- 13 lists the physiological significance, deficiency symptoms and main sources of several major trace elements.
Table 9- 13 Physiological Functions, Deficiency Symptoms, Main Sources and Supply Standards of Several Major Trace Elements
Medical experts believe that more than 90% of human diseases today are related to the "poverty" and "wealth" of trace elements in the human body. Many difficult and endemic diseases are related to the imbalance of trace elements in the human body. Maintaining the normal dynamic balance of trace elements in the human body can only be achieved through material exchange between the human body and the environment. In other words, the environmental geochemical distribution of elements has a direct and very important impact on human health. When people live in a natural environment with low or excessive element content for a long time, it will inevitably lead to the imbalance of some elements in the human body, which will lead to organ and tissue diseases, also known as "endemic diseases". The occurrence of endemic diseases is closely related to geographical location, topography, geology, hydrology, climate and living habits of residents. The most common geochemical endemic diseases are mainly thyroid, fluorosis, Keshan disease and Kaschin-Beck disease.
(2) Goiter
Goiter, also known as goiter, is an endemic disease caused by iodine deficiency or iodine enrichment in the environment. Iodine deficiency disorder (IDD) is an endemic disease that seriously harms human health and affects children's intellectual development. It mainly affects the normal development of human body, the function of brain and nervous system and the maintenance of body heat. Mild manifestations of goiter (commonly known as big neck disease), known as endemic goiter; On the other hand, it is characterized by developmental retardation, deafness, short stature and paralysis, which is called endemic cretinism (commonly known as cretinism). Endemic goiter caused by severe iodine deficiency can occur in children and adults. If pregnant women are seriously deficient in iodine during embryonic brain development, it can lead to fetal brain hypoplasia, and the clinical symptoms after birth are stupidity, short stature, deafness, deafness and paralysis.
Iodine is one of the essential trace elements in human body, which is related to the development of physique and intelligence, the functions of nerves, muscles and circulation, and the metabolism of various nutrients. The total amount of iodine in healthy adults is about 20 ~ 50 mg, and the daily iodine requirement is about 50 ~ 200 micrograms. 70% ~ 80% of iodine in human body exists in human thyroid gland, which is used to synthesize thyroid hormone, regulate human metabolism and promote human growth and development. The main sources of iodine in human body are food and water. However, due to the differences in geological and historical changes during the development of the earth, the distribution of iodine on the crust surface is uneven. Generally speaking, the earth is lower than the ocean, the mountains are lower than the plains, and the plains are lower than the coast. Therefore, most mountainous areas, plateaus and a few plain areas lack iodine, and people living in these areas cannot get enough iodine.
1. Geology and geographical distribution of iodine
Goiter is a common endemic disease, which occurs in many countries and regions in the world. The more serious epidemic areas are distributed in Himalayas, Alps, Caucasus and the west coast of America. Almost all the hardest hit areas occur in remote mountainous areas and areas with low economic living standards. At present, there are about 654.38 billion people living in iodine deficiency areas, about 200 million people suffering from endemic goiter and 3 million people suffering from endemic cretinism.
China is a country seriously threatened by iodine deficiency disorders. About 425 million people live in iodine deficiency areas, and 65.438+0.5 million people suffer from endemic goiter and severe cretinism, mainly distributed in mountainous areas such as northwest, southwest, south-central, northeast and north China. About 90% of the millions of dementia patients in China are caused by iodine deficiency.
The geochemical characteristics of iodine determine the uneven distribution of iodine in nature, so the distribution of goiter is obviously affected by geological factors. The formation with low organic matter content or rich organic matter is undeveloped or missing, and the iodine content in drinking water and soil is insufficient, which will cause goiter. Excessive iodine can also cause this disease.
2. Geochemical characteristics of iodine
Primary iodine exists in crustal rocks, or is directly ejected from the surface through volcanoes. Iodine is an extremely active component, which is easily oxidized in the surface environment and often exists in the form of molecules or compounds. In the process of geochemical evolution, iodine is relatively rich and poor, with low abundance in polar and alpine areas and high abundance in depressions and coastal areas; There are few wet and leaching areas and many dry areas; Less common in granite and quartzite, more common in basalt and marine shale; Less in calcareous soil and sandy soil, more in swamp soil, humus soil, chernozem soil and saline soil.
The content of iodine in natural water varies greatly. In the atmospheric precipitation, the coastal area is 2 μ g/L, and the inland area is 0.2 μ g/L; The iodine content in mountain surface water and shallow groundwater is low, ranging from 0 to 0.2 μ g/L; The plain area is relatively high, which is 5 ~100μ g/l; The saline-alkali area is about10 ~ 30μ g/L. The iodine content in seawater is relatively high, reaching 50μ g/L. Generally, it is 5 ~ 100μ g/L in oil fields, and the highest is 500μ g/L. ..
Due to the enrichment of iodine by organisms, the iodine content in organisms is relatively high. The iodine content in marine organisms is 100 ~ 1000 times higher than that in the crust, and that in terrestrial plants is 10 times higher than that in the crust. So generally speaking, the iodine content in organic matter is relatively high, and the iodine content in soil rich in organic matter is also relatively high. Biological enrichment of iodine can enrich iodine in petroleum and asphaltene sediments and become the main source of iodine resources.
3. Biochemical effects of iodine
Iodine is an essential trace element for human body, and its content is small but its function is very important. Iodine is synthesized into thyroxine in the thyroid gland, and each thyroxine molecule must have four iodine atoms. Therefore, the lack of iodine in human body can not synthesize thyroxine, which leads to compensatory hyperplasia of thyroid tissue and nodular uplift in the neck, that is, goiter.
4. Pathogenic mechanism and prevention
The causes of goiter are complicated. The factors leading to the disease are geological geography, soil, water, food and sanitary conditions (Table 9- 14). In the natural environment, there are factors that interfere with the human body's absorption of iodine, such as drinking water with more elements such as calcium, fluorine, magnesium, zinc, copper and lithium, or water rich in humic acid and microorganisms, which can affect the human body's absorption of iodine. In addition, eat milk (there are too many cruciferous plants in the pasture), Brassica plants, soybeans and so on. It will also affect the utilization of iodine and induce goiter. These foods contain more perchlorate, thiocyanate and nitrite. They are called thyroid-causing substances.
At present, the pathogenesis of iodine-excess goiter is not very clear, and most scholars believe that it is closely related to iodine blocking effect. Whether normal people or patients with various thyroid diseases, when a large amount of potassium iodide or organic iodine is given, it is difficult for iodine ions to enter the thyroid tissue, which is called iodine blocking.
Table 9- 14 factors affecting endemic goiter
The prevention of iodine deficiency disorders is mainly to supplement iodine for iodine-deficient people. At present, we mainly choose suitable drinking water and food, or take iodized salt and oral iodized oil pills, inject iodized oil, eat iodized food and other methods. Practice at home and abroad has proved that eating iodized salt is an effective, economical, safe and convenient measure. As long as people in iodine-deficient areas adhere to and correctly eat iodized salt and give iodized oil pills to women of childbearing age, the emergence of new cretinism patients can be effectively controlled and iodine deficiency disorders can be eliminated. The application of iodine-rich agricultural fertilizer can also increase the iodine content in grains, thus providing high iodine content for people in iodine-deficient areas.
(3) Endemic fluorosis
Endemic fluorosis, also called endemic fluorosis. It is a chronic toxic disease caused by drinking high-fluorine water or eating high-fluorine food for a long time. Endemic fluorosis is widely distributed in the world, with a high incidence in more than 30 countries. Fluorosis is prevalent in different degrees in all parts of China. There are about 762 counties (banners) in China, accounting for about one-third of all counties (banners) in China, mainly distributed in Heilongjiang, Jilin, Ningxia, Inner Mongolia, Shaanxi, Henan, Shandong and other provinces, and the affected population is about 45 million.
1. Geological geographical distribution
The spatial distribution of fluorosis is closely related to the epigenetic geochemical environment, which is mainly restricted by rocks, topography, hydrogeochemical conditions, soil and climate. High fluorine areas may appear near volcanoes, exposed areas of high fluorine rocks, near hot springs, coastal areas and arid and semi-arid areas.
Volcanic ash, volcanic gas and other ejecta contain a lot of fluorine, which is distributed around the crater in a ring shape. Residents living around the volcano suffer from dental fluorosis and fluorosis. Some famous volcanoes in the world, such as Mount Vesuvius in Italy, Mount Naples and volcanic areas in Iceland, all have endemic fluorosis.
The exposed areas of high fluorine rocks and fluorine mining areas are also the incidence areas of endemic fluorosis. For example, fluorite, cryolite, dolomite, limestone and fluorophosphate are rich in fluorine, which can increase the fluorine content in surface water and groundwater during weathering, leaching, migration and transformation.
Spring water above 20℃ can also dissolve many minerals. The fluorine content of hot spring water is generally higher than that of surface water, and it also increases with the increase of spring temperature, so fluorosis often occurs in hot spring areas. In many hot spring areas in China and Tibet, the fluorine content of spring water is as high as 9.3 ~ 15 mg/L, and the residents around the hot springs suffer from severe fluorosis.
In coastal areas, due to long-term seawater infiltration, a salt-rich geochemical environment has been formed, and fluorine in seawater is easy to be enriched here. Seawater intrusion caused by extensive exploitation of groundwater in coastal areas not only makes soil salinized and wells scrapped, but also increases the fluorine content of groundwater, thus causing fluorosis. Tianjin, Cangzhou, Weifang and other coastal areas in China are all high incidence areas of fluorosis.
Arid and semi-arid areas have dry climate, less precipitation, strong surface evaporation, poor groundwater flow and high fluorine concentration, which are easy to form fluorine-rich areas and high incidence areas of fluorosis. Many areas in India are rich in fluorine, with the total amount of 12× 106t (about 85x 1 06t in the world), and the number of patients with endemic skeletal fluorosis exceeds110,000.
2. Geochemical characteristics of fluorine
There are two natural sources of fluorine: ① Weathered minerals and rocks; ② Volcanic eruption. Due to different natural and geographical conditions, the fluorine content in soil varies greatly. Fluorine migrates in the form of complex in acidic environment, and is mostly ionic in alkaline environment. The fluorine content in surface water and groundwater is closely related to the climate zone. The calcareous soil zone in humid climate zone belongs to acidic leaching environment, which is beneficial to fluorine migration. The fluorine content in water is generally 0.05 ~ 0.20 mg/L; The fluorine content in chernozem and chestnut soil in arid and semi-arid grassland is higher than that in saline soil and alkaline earth, and the fluorine content in water in arid grassland climate zone can reach 2 ~12 mg/L.
Fluorine is widely distributed in natural water, but it is extremely uneven. According to research, the fluorine content in seawater is about 0. 1 mg/l, river water is 0.03 ~ 7 mg/l, hot spring water is 1.5 ~ 1.8 mg/l, and salt lake water is as high as 20 ~ 40 mg/l. The fluorine content in natural water is also affected by topography and groundwater runoff conditions. Generally, the mountains are low and the plains are high; The hills are low and the depressions are high. In areas with poor groundwater runoff conditions, the fluorine content in water is relatively high.
3. Pathogenic mechanism and prevention
Fluorine (F) is an essential element in the process of human life and has important physiological functions. It exists in all parts of the human body. The normal fluoride requirement per person per day is about 1mg, and the adult health maintenance requirement published by Japanese and American nutrition research institutions is 2. 1 ~ 2.3 mg.
80% ~ 85% of fluoride in human body is concentrated in bones and teeth. The fluoride content of adult teeth is 1 1mg/ 100g, while the fluoride content of patients with dental caries is only 6 mg/ 100 g. Keeping a certain amount of fluoride in drinking water or taking an appropriate amount of fluoride from food can inhibit the enzymes needed by bacteria to decompose sugar, strengthen the protective layer of alkyl apatite in enamel and prevent dental caries. The mechanism is that fluorine can replace a part of hydroxyl groups of hydroxyapatite in enamel to form acid-insoluble crystals, thus enhancing the resistance of oral microorganisms to acid production. If the fluoride intake is insufficient, the process of fluoride transformation into enamel will be hindered, thus promoting the formation of dental caries. Domestic survey data show that the dental caries rate of residents in areas with fluorine content below 0.5mg/L is generally 50% ~ 60%; In areas where the fluoride content in water is 0.5 ~ 1.0 mg/L, the dental caries rate of residents is generally only 30% ~ 40%.
If more than 4 mg of fluoride enters the human body every day, the ingested fluoride is absorbed and deposited in bone tissue, which will lead to fluorosis. Mild fluorosis is characterized by "mottled glaze disease", which causes fluorosis; Suffering from dental fluorosis, the tooth surface loses luster and roughness, and some appear yellow, brown and black pigmentation. This disease is found in many areas of northern China, which can lead to flaky or massive defects, enamel damage and shedding. Investigations in several regions of China show that under normal circumstances, when drinking water containing 0.5 ~ 1.0 mg/L of fluorine, the prevalence of dental fluorosis is 10% ~ 30%, and most of them are mild enamel spots; When 1.0 ~ 1.5 mg/L, the incidence of dental fluorosis in most areas has reached more than 45%, and the number of moderate and severe patients has increased significantly. Dental fluorosis is an early sign of excessive fluoride intake and one of the main indexes to evaluate the severity of endemic fluorosis.
The worst case is "skeletal fluorosis". At the early stage, patients with skeletal fluorosis suffered from pain in limbs, spine and joints and general weakness. In severe cases, bone deformation, joint lesions, palm cortex thickening and cracking, limb dysfunction, lumbar spine deformation, hunchback, and even loss of labor ability or paralysis may occur. This disease is common in Yanchi, Jaboulay, Alashan Right Banner, Inner Mongolia, China, because the fluorine content in drinking water reaches10 mg/L.
According to foreign reports, fluoride intake is about 10mg/kg (body mass), which may cause acute poisoning. After taking 15 ~ 20 mg daily for 10 years, skeletal fluorosis may occur; Daily intake of 20 mg for more than 20 years can lead to disability. The fluorine content in drinking water is 8 ~ 20 mg/L, which will cause damage if it is drunk for a long time. 3 ~ 8 mg/L can cause skeletal fluorosis; When it exceeds 10mg/L, it will lead to disability.
Fluorine is also closely related to tumors. According to the report of the American Cancer Institute, one tenth of the 350,000 cancer deaths in the United States each year are related to drinking fluoride-containing water (artificially adding fluoride to drinking water). Some people used inorganic fluoride as mutagenic activity test in rats, and the results showed that fluorine was a typical inorganic mutagen. Chinese scientists and technicians investigated the fluoride in drinking water of Inner Mongolia 10 flags, and found that 8 flags were higher than the allowable amount stipulated by national standards. Among the common 65,438+06 malignant tumors, 65,438+065,438+0 are positively correlated with fluoride in drinking water, which has a significant impact on stomach, esophagus and brain tumors.
About 65% fluoride in human body comes from drinking water and 35% from food. The effect of fluorine content in water on human body is shown in Figure 94. The regulations of fluorine content in drinking water in different countries are not consistent. For example, The drinking water quality standard formulated by the World Health Organization (WHO) guides countries all over the world to formulate drinking water quality standards, and the limit of fluorine content is1.5mg/l The drinking water quality directive formulated by the European Union, which guides EU countries to formulate drinking water quality standards, stipulates that the maximum allowable value of fluorine is 0.7 ~ 1.5 mg/ L The U.S. Provisional Regulations on National Drinking Water stipulates that the fluorine content in drinking water is 1.4 ~ 2.4 mg/L (depending on the ambient temperature), while most other countries are1.0 ~1.5 mg/L. According to China's drinking water standard, the fluorine content in water is 0.5 ~/kloc-0.
From the point of view of preventing dental caries, when the fluorine content in drinking water is lower than 0.5mg/L, we can consider adding a certain amount of fluoride into the water, which is called drinking water fluorination. Fluorination of drinking water is adopted in many places in the United States, and fluoride was added to tap water in China and Guangzhou in the past. Later, fluoride was stopped because it could be supplemented by factors such as diet.
From the point of view of preventing fluorosis, fluoride removal should be considered when the fluorine content in drinking water reaches 1.5mg/L or higher. There are many ways to remove fluoride. The most convenient method is to flocculate and precipitate with sulfuric acid or lime, but the efficiency is poor. In areas where electricity is cheap, distillation can be considered, that is, distilled water is made from fluorine-containing water. Defluorinated water can also be produced by freezing method. After the fluorine-containing water freezes, the ice cubes melt and relatively pure water is obtained. Usually, the defluorination agent adsorption defluorination method is adopted, and the defluorination agent is used to filter fluorine-containing water at a certain filtration speed, so that the effluent from the filter column can meet the specified requirements of fluorine content in drinking water. The defluorinating agents used are: tricalcium phosphate, ashes and activated alumina. The former two have poor mechanical strength, and strong alkali and strong acid are used for regeneration, which is inconvenient to use. Activated alumina has good mechanical strength, and it is popular to regenerate without strong alkali and strong acid. Electrodialysis, reverse osmosis and ion exchange can also be used to remove fluoride from water, and fluoride can also be removed at the same time of desalination. However, the process is complex, the operators need some training and the equipment investment is high. These methods are usually used for water with high salt content and fluorine content.
Fig. 9-4 Effect of Fluorine Content in Water on Human Bone and Tooth Growth
In addition, reducing the fluorine content in food, limiting the combustion of high-fluorine coal and the discharge of fluorine-containing "three wastes" into the environment by industrial and mining enterprises are measures to prevent food-borne fluorosis and fluorosis caused by smoke pollution from high-fluorine coal.
Kaschin-Beck disease
Kaschin-Beck disease is a kind of deformed osteoarthropathy that seriously harms human health. This disease is widely distributed all over the world. Although 100 has been studied for many years, the reason has not been thoroughly ascertained.
China is the country with the largest number of cases of Kaschin-Beck disease, and the endemic areas are distributed in the transitional zone between the humid monsoon area and the inland arid area in the east of China, with a strip distribution from the northeast to Tibet, including 296 counties (cities, autonomous regions and so on). 15 Heilongjiang, Jilin, Liaoning, Inner Mongolia, Shanxi, Beijing, Shandong, Hebei, Henan, Shaanxi, Gansu, Sichuan, Qinghai and Tibet provinces and Taiwan Province Province. Among them, Heilongjiang Province (66 counties and cities) suffered the most. Russia's Siberia, North Korea, Sweden, Japan, Vietnam and other countries and regions have also occurred.
1. Geological geographical distribution
Kaschin-Beck disease is widely distributed, spanning three climatic zones: cold zone, temperate zone and tropical zone, and the natural environment is complex and changeable. The geological and geographical environment of epidemic areas can be divided into supergene natural humus environment, swamp facies sedimentary environment, loess plateau gully environment and desert swamp sedimentary environment.
The natural humus environment area is rich in humus, and the soil is mostly brown and dark brown forest soil, meadow swamp soil and swamp soil. In this area, Kaschin-Beck disease is more serious among people who often drink marsh dianzi water, ditch water or pore seepage spring water, but less or no disease occurs among people who mainly drink river water, bedrock spring water or deep well water.
The sedimentary environment of swamp facies is mainly distributed in plain areas, such as Songliao Plain, Songnen Plain and Sanjiang Plain in the northeast, and the natural landscape is mainly semi-arid grassland. The terrain in this area is low and flat, the water is not smooth, and swamps and lakes are dotted. The occurrence of Kaschin-Beck disease mainly depends on the exploitation horizon of groundwater. Anyone who exploits groundwater in lakes and swamp sediments is more frequent and serious.
The gully region of the Loess Plateau has strong erosion and serious soil erosion. Local residents often drink pit water, ditch water, seepage spring water and seepage well water, but the groundwater quality in these areas is poor, which often induces Kaschin-Beck disease.
2. Pathogenic mechanism and prevention
The pathogenesis of Kaschin-Beck disease has not yet been determined. Judging from the age of patients, children and adolescents are common. The main symptoms are joint pain, joint thickening and deformation, dyskinesia and muscle atrophy, which can affect normal life lightly, and completely lose the ability to work and live in severe cases. Over the years, scholars at home and abroad have put forward many hypotheses about the cause of the disease, such as biogeochemistry, food-borne fungal poisoning and comprehensive ecological effects, among which biogeochemistry hypothesis is the most popular.
(1) biogeochemical theory
Biogeochemistry holds that Kaschin-Beck disease is a disorder of mineral metabolism, and its pathogenic mechanism is caused by the lack, surplus or imbalance of some elements in soil, water and plants in the endemic area. Some people think that lack of calcium, sulfur, selenium and other elements in the environment or excessive metal elements such as copper, Bb, zinc, nickel and molybdenum will cause diseases. Some people think that the imbalance of elements in the environment, such as more Sr and less Ca, more Se and less SO _ 2-4, or more Si and less Mg, is the main cause of the disease. Kaschin-Beck disease is also related to the high content of humic acid in the environment.
(2) the theory of food-borne fungal poisoning
According to the theory of food-borne fungal poisoning, Kaschin-Beck disease is caused by food (corn and wheat) contaminated by toxic Fusarium in epidemic areas, and residents are poisoned by eating this food for a long time. Inoculating animals with virulent strains of Fusarium can cause pathological changes in animal bones similar to Kaschin-Beck disease.
(3) comprehensive ecological effect theory
According to the comprehensive ecological effect theory, Kaschin-Beck disease is caused by many ecological factors, such as abnormal distribution of elements in the environment, food mildew, lack of protein and vegetables, improper lifestyle, etc., which leads to "periosteal defect" as the main cause of Kaschin-Beck disease.
The fundamental principle of prevention and treatment of Kaschin-Beck disease is to eliminate pathogenic factors and actively adjust and improve environmental conditions. Practice has proved that improving water and preventing diseases is one of the most effective measures at present. Through animal experiments and chondrocyte experiments, it is proved that selenium (Se) can inhibit the toxicity of humic acid and Fusarium toxin in water. If the content of humic acid in drinking water in ward is controlled below 0.05 mg/L, obvious effect can be achieved. In addition, advocating omnivore, strengthening nutrition and taking Na _ 2 SEO _ 3 tablets in moderation also have certain preventive and therapeutic effects on Kaschin-Beck disease.
(5) Keshan disease
Keshan disease is a widely distributed endemic disease, which occurs both at home and abroad and has the characteristics of regional distribution. In the early 1970s, Chinese scientists found that Keshan disease was related to selenium deficiency in the body, and moderate intake of selenium had obvious preventive effect on Keshan disease. Clinical observation shows that Keshan disease is a kind of nutritional deficiency and belongs to biogeochemical disease. The main symptoms of Keshan disease are heart enlargement, cardiac insufficiency, cardiogenic shock or heart failure, arrhythmia, tachycardia or bradycardia, etc. This is a serious myocardial disease. The distribution of Keshan disease in China is related to thick continental deposits in Mesozoic and Cenozoic, and is also closely related to topography. Geographically, it is a diagonal strip from northeast to southwest. According to statistics, there are 15 provinces and 303 counties (banners) in China with Keshan disease distribution.
1. Geological geographical distribution
The distribution of Keshan disease in China can be divided into three types: northeast, northwest and southwest. The common feature of these areas is that they are rich in humus.
The characteristic of Keshan disease in Northeast China is that most patients with Keshan disease suffer from Kaschin-Beck disease, and its distribution is basically the same as the severity of the disease. The natural environment is mainly supergene natural humus environment and lacustrine sedimentary environment. Most residents in the ward drink underground diving or surface water rich in humic acid.
Keshan disease in northwest China is represented by loess plateau in northern Shaanxi and loess plateau in eastern Gansu. Residents in the ward often drink kiln water, seepage spring water and ditch water polluted by organic matter.
Keshan disease in southwest China is mainly distributed in Yunnan Plateau and hilly areas in eastern Sichuan. Residents in the ward often drink ditch water, pit water and waterlogged pool water with poor water quality and serious organic pollution.
2. Pathogenic mechanism and prevention
The biogeochemistry of Keshan disease has made great progress. According to the systematic study of humic acid by Lin Nianfeng et al. (1990), Keshan disease is related to excessive humic acid in drinking water. Humic acid may cause Keshan disease in two ways.
1) forms complexes or chelates with various elements, which further affects the absorption of iron, manganese, magnesium and other elements, leading to the lack of these trace elements and causing diseases.
2) The toxicity of low molecular weight humic acid directly damages myocardium and causes diseases.
High levels of nitrite and barium in the environment can also cause poisoning, leading to Keshan disease.
In addition, there are some viewpoints about the pathogenic mechanism of Keshan disease, such as the theory of nutritional deficiency and the theory of biological etiology. According to the theory of nutritional deficiency, the food in the endemic area is short of vitamins A, B, C and amino acids, while the theory of biological etiology holds that Keshan disease is a natural focus disease caused by virus, belonging to myocarditis caused by virus infection or cardiomyopathy caused by some fungal poisoning in food. Some virologists believe that one or more viruses in Keshan disease area interact with each other due to suitable water and soil conditions, and directly or indirectly affect the heart and muscles.
The prevention and control measures of Keshan disease are mainly to improve water or change water to prevent pathogenic factors from entering the human body. In the environment with low selenium content, increasing selenium intake by taking medicine can also play a role in preventing and treating diseases.
In recent years, the research of environmental medicine shows that the high incidence area of cancer also has the characteristics of regional distribution, which shows that geochemical environment is also one of the important factors of carcinogenesis. Lack of molybdenum in human body may cause esophageal cancer and liver cancer. For example, Linxian county, Henan province, China is a high incidence area of esophageal cancer, and the geochemical environment of the area is characterized by a serious lack of Mo. Some areas in the Yangtze River Delta are also high incidence areas of liver cancer with molybdenum deficiency.