Dietary minerals are vital inorganic nutrients required by living organisms to remain healthy. There are two types of nutritional elements required in our diets: macro/ major minerals and micro/trace minerals. Macro minerals are those that are required in our diets in amounts greater than 100 milligrams per day. Macro minerals make up about 0.01 % of human body weight. The seven macro minerals are calcium, phosphorus, magnesium, sodium, potassium, chloride and sulphur. Trace minerals are those that are required in amounts less than 100 milligrams daily. The nine trace minerals include iron, copper, zinc, iodine, fluoride, selenium, cobalt, chromium and molybdenum.
Occurrence and importance
There are over 90 naturally occurring elements. Of these only 26 are known to be necessary in humans. The four common elements, oxygen, carbon, hydrogen and nitrogen – make up 96% of the total weight of a mammal. The remaining 4% is the most abundant seven macro minerals. They constitute 60-80% of all the inorganic material in the body. Dietary minerals are essential for life and an insufficient supply may cause disease. They help form bones and teeth, aid in normal muscle and nerve activity, act as catalysts in many enzyme systems, help control water levels in the body and are components of enzymes and hormones and compounds like haemoglobin. Minerals like sodium, chloride and potassium are referred to as electrolytes because in water they can conduct electrical currents. They are essential for maintaining tissue fluid balance and the movement of nutrients and waste products in the cells.
Calcium is a major constituent of bones and teeth and is the body’s most abundant mineral. About 99% of the body calcium is present in the bones as calcium phosphate (calcium to phosphorus ratio is 2:1). Adequate intake of calcium for adults is 1000 milligrams per day whereas pregnant and nursing mothers require more calcium. Most calcium comes from dairy foods like milk, cheese and yogurt. Other food sources rich in calcium include bok choy, broccoli, kale and spinach. A deficiency of calcium can lead to osteomalacia, osteoporosis, rickets, and tachycardia. Calcium ions are needed for membrane permeability, nerve conduction, muscle contraction and blood clotting.
Phosphorus is the body’s second most abundant mineral found in every cell and as part of DNA and RNA. The main sources of phosphorus include milk, cheese and meat. Adults need 700 milligrams of phosphorus daily.
Potassium is the third most abundant mineral in the body. Dietary sources of potassium include chicken, beef, pork, banana, orange, straw berries, pine apples, carrots and broccoli. It is the principal intracellular cation. It regulates acid-base balance and osmotic pressure of intracellular fluid. Adults require 4700 milligrams each day.
Sulphur is the fourth most abundant body mineral. Sulphur is the constituent of proteins, amino acids, vitamins, insulin, heparin, and chondroitin sulphate. Eating protein rich foods like meat, fish, poultry, eggs, and milk provide enough sulphur and legumes give the required amounts of suphates for the body.
Sodium and chloride are the fifth most abundant minerals in the body and are both electrolytes that help to maintain fluid and electrolyte balance. Sodium is the major extracellular cation and chloride is the inorganic anion. Significant sources of sodium and chloride include table salt, soy sauce and processed foods. Adequate intake of sodium is 1500 milligrams for people from ages 19 to 50 and recommended upper limit for adults is 2300 milligrams per day. Adequate intake of chloride is set at 2300 milligrams with an upper limit of 3600 milligrams a day.
Magnesium is the sixth most abundant mineral in the body and last of the major minerals. More than 300 enzymes are known to be activated by magnesium ions. Magnesium works with calcium to assist in muscle contraction, blood clotting and the regulation of blood pressure and lung function. Dietary sources of magnesium include halibut, cashews and artichokes. Adequate intake for magnesium is 410 milligrams for males and 360 milligrams for females.
There are 15 elements that make up less than 0.01% of the body of a mammal. The trace minerals are required in small amounts, hence the name ‘trace minerals’. At present, only 9 trace minerals have defined essential functions in humans. Iron, zinc and copper are considered essential trace elements. A number other minerals have been suggested to be essential nutrients including arsenic, boron, bromine, cadmium, fluorine, lead, lithium, nickel, silicon, tin and vanadium. Trace minerals have four known roles in living organisms. They work in close association with enzymes, coenzymes and proteins. Some trace minerals donate or accept electrons in redox reactions of metabolic pathways. Some trace mineral especially iron, bind, transport and release oxygen in the body. Some trace minerals provides stability and structure to biomolecules. Under the deficiency of trace minerals, the organism survives but with suboptimal health and wellbeing. If the dietary intake is reached, the optimal health and wellbeing are regained.
Iron is one of the most essential trace elements. Iron is a constituent of haemoglobin and several intracellular enzyme systems like cytochrome oxidase, catalase, and xanthine oxidase. The body content of iron is 4-6g. The dietary requirement of iron is very small because the iron from break down of haemoglobin is stored in the liver and used again for haemoglobin synthesis. The dietary source of iron includes liver, kidneys, heart, spleen, egg yolk, fish and oyster.
Zinc is the second most abundant trace mineral. It is a constituent of zinc dependent enzymes e.g., DNA polymerase, alkaline phosphatase, carboxypeptidase etc. The body content is 2.5 grams and the daily requirement is 3 – 14 milligrams. Diet rich in zinc include red meat, fish and sea foods. Zinc deficiency in children results in growth retardation and skeletal abnormalities. Zinc deficiency also leads to complications of pregnancy and childbirth, low birth weight and poor growth in childhood, reduced immunocompetence, and increased infectious disease morbidity.
Copper is the third most abundant trace mineral in the human body. Body content of copper is 80-120mg. Copper is involved in the process of erythropoiesis, erythrocyte function and regulates erythrocyte survival. The daily dietary requirement is between 2 – 6 milligrams, which is mainly obtained from red meat, cocoa, shell-fish, water pumped through copper pipes and chocolates.
Selenium (ultra trace mineral) is the least abundant however the most toxic of all the essential elements. Dietary source is meat, fish and grains. The recommended intake for adults 50 - 200 µg/day as in USA however intake may vary in other countries where soil Selenium levels are low. Selenium deficiency occurs due to hemolytic anaemia and malnutrition.
Manganese (ultra trace mineral) is an important role in regulating metabolic processes which mainly include lipid and carbohydrate metabolism, bone and tissue formation, skeletal growth and reproduction. Over 50 Manganese dependent enzymes have been identified e.g., catalase, peroxidase, super oxide dimutase, 5’ nucleotidase, R Nase and glucosyl- and glactosyl-transferase. Average daily body requirement is 2-5μg/day.
Cobalt (ultra trace mineral)-Biological function is limited. Vitamin B12 is the only cobalt containing compound. Beef, sea food and dairy products are major source of vitamin B12.
Iodine is necessary for the synthesis of the thyroid hormone. Enlargement of the thyroid gland occurs when iodine intake is less than 15 µg/day. Maternal iodine deficiency during pregnancy gives rise to cretinism in infants. Iodine deficiency during the foetal and early neonatal period adversely affects the growing brain.
The human body needs a number of minerals in trace (milligram) quantities. Other minerals are required in ultra trace (microgram) amounts. The dependence of many vital metabolic processes on trace elements confers upon them a physiologic importance analogous to that of vitamins.