Minerals in the human body

Minerals in the human body

“Minerals help our bodies develop and function.  They are essential for good health. Knowing about different minerals and what they do can help you to make sure you get enough of the minerals that you need.”

Major minerals present in the human body are sodium, potassium, chloride, calcium, phosphate, and magnesium The daily body requirements for minerals range from gram (sodium, calcium, chloride, phosphorus) to the milligram (iron, iodine, magnesium, manganese, molybdenum) to microgram (zinc, copper, selenium, other trace elements) amounts. Many are essential for normal biological function.

Sodium and chloride are important for the maintenance of osmolality of the extracellular fluid and cell volume. Sodium participates in electrophysiologic phenomena and, together with potassium, is essential for maintaining transmembrane potential and impulse transmission. Potassium is the main intracellular cation.

Potassium is contained in vegetables and fruit, particularly bananas, and in fruit juices. Dietary potassium intake needs to be limited in renal disease because of its impaired excretion and a consequent tendency to hyperkalemia. Importantly, both hyperkalemia and hypokalemia may lead to life-threatening arrhythmias.

Magnesium functions as a cofactor for many enzymes and are also important in the maintenance of membrane electrical potential. Its role is linked to that of potassium and calcium. It is important for skeletal development and the maintenance of electrical potential in nerve and muscle membranes. It is also a cofactor for ATP-requiring enzymes and is important for the replication of DNA, and RNA synthesis. Magnesium deficiency develops in starvation and malabsorption, may be due to the loss of the gastrointestinal tract in diarrhea and vomiting, and sometimes occurs as a result of diuretic treatment and surgical procedures on the gastrointestinal tract. It is also associated with acute pancreatitis and alcoholism. Hypomagnesemia is often accompanied by hypocalcemia and hypokalemia. Magnesium deficiency leads to muscle weakness and cardiac arrhythmias.

Calcium and phosphate are essential for bone metabolism, secretory processes, and cellular signaling. Calcium is present in milk and milk products, and some vegetables. Phosphates are abundant in plant and animal cells.

 Iodine is essential for the synthesis of thyroid hormones. The iodine content of food depends on the composition of the soil where it is grown. Marine fish and shellfish have the highest content. It is also present in freshwater fish, meat, and dairy products, as well as in legumes, vegetables, and fruit.

Fluoride influences the structure of the bone and teeth enamel. In many areas, fluoride is added to water to prevent tooth decay. Excess leads to teeth discoloration and fragility of bones.

Iron

Iron is important in the transfer of molecular oxygen

 Iron is a component of heme in hemoglobin and myoglobin. Cytochromes a, b, and c also contain iron. Altogether, there are 3– 4 g of iron in the body. Seventy-five percent of body iron is in hemoglobin and myoglobin, and 25% is stored in tissues such as bone marrow, liver, and reticuloendothelial system. Dietary sources of iron include organ meats, poultry and fish, oysters, and also egg yolks, dried beans, dried figs and dates, and some green vegetables.

Iron is transported in plasma bound to transferrin

 Iron is absorbed in the upper small intestine. Meat and ascorbic acid increase its absorption, and vegetable fiber inhibits it. It is transported in the blood bound to transferrin and is stored as ferritin and hemosiderin. Transferrin is normally about 30% saturated with iron. Iron is lost through the skin and the gastrointestinal tract. Dietary iron is in the ferric (Fe 3+) form. It is reduced in the gastrointestinal tract to divalent Fe 2+ by ascorbate and a ferrireductase enzyme located in the intestinal brush border. Fe 2+ is transported into the cells by a divalent metal transporter (which also transports most trace metals). The iron pool within the enterocyte is controlled by the iron regulatory proteins.

 Erythrocyte content of iron affects its absorption from the intestine

If erythrocytes are iron-rich, the iron is stored in the enterocytes and incorporated into ferritin. Otherwise, it is transported through the basolateral membrane, where one of the transport-facilitating proteins, ferroxidase, also called hephaestin, oxidizes Fe 2+ to Fe 3+, which is then bound to transferrin in plasma. Transferrin is taken up in the bone marrow by erythrocyte precursor cells in a receptor-dependent manner. Within the cells, iron is released, again reduced to Fe 2+, and transported to the mitochondria for incorporation into heme in the Fe 2+ form. After the destruction of the old erythrocytes by macrophages in the reticuloendothelial system, the iron is released as Fe 2+, re-oxidized to Fe 3+, and loaded back onto transferrin.

 

 

Trace elements

 Zinc

Zinc is a component of numerous (approximately 100) enzymes associated with carbohydrate and energy metabolism, protein synthesis and degradation, and nucleic acid synthesis

 It plays a role in cellular transport and protection from oxidative damage, as well as immune function, cell division, and growth. Spermatogenesis is also zinc-dependent. Zinc plays a role in maintaining exocrine and endocrine pancreatic function. Its effects are most obviously seen in the maintenance of skin integrity and wound healing.

Copper

 Copper scavenges superoxide and other reactive oxygen species

 Copper is associated with oxygenase enzymes including cytochrome oxidase and superoxide dismutase (the latter also requires zinc). One of the main roles of copper, especially in superoxide dismutase but also in association with the plasma copper-carrying protein ceruloplasmin, is the scavenging of superoxide and other reactive oxygen species. Copper is also required for the crosslinking of collagen, being an essential component of lysyl oxidase.

 

Selenium

 Selenium is present in all cells as amino acids selenomethionine and selenocysteine

 Selenium is a component of selenoproteins, which contain the amino acid selenocysteine. The antioxidant enzyme glutathione peroxidase is a selenoprotein, as are the iodothyronine deiodinases, enzymes that produce triiodothyronine (T3) and reverse T3 (rT3). Thioredoxin reductases that participate in cell proliferation apoptosis and DNA synthesis also contain selenocysteine. Selenium affects functions of the immune system, including stimulation of differentiation of T cells and proliferation of activated T lymphocytes, as well as an increase in natural killer cell activity. It also plays a role in spermatogenesis. Selenium is absorbed in the small intestine. It remains protein-bound in circulation and is excreted in the urine. Selenoprotein P possesses 10 selenocysteine residues and it transports selenium in plasma from the liver to, primarily, the brain, testis, and kidney. In the brain, it binds to a membrane receptor apoER2, which belongs to the family of lipoprotein receptors. Selenium is present in the diet as selenomethionine and selenocysteine. Brazil nuts are its richest source. Its dietary sources also include organ meats, fish (tuna), and shellfish.

Other metals

Numerous other trace metals are required for normal biological function: for example, manganese, molybdenum, vanadium, nickel, and cadmium. Some, similar to zinc and copper, form prosthetic groups of enzymes. These include molybdenum (xanthine oxidase) and manganese (superoxide dismutase and pyruvate carboxylase) Chromium has been associated with glucose tolerance. Many of these metals were previously thought to be toxic; indeed, their environmental excess does result in toxicity such as the renal toxicity observed in shipyard workers exposed to cadmium over long periods. As techniques for separation and analysis develop, other metals and other functions of known essential minerals will become known. This will lead to a better understanding of the epidemiology of certain diseases that may have, at least in part, an environmental etiology.