In nutrition, a mineral is a chemical element. Some minerals are essential for life, but most are not. Minerals are one of the four groups of essential nutrients, the others being vitamins, essential fatty acids and essential amino acids.
The five major minerals in the human body are calcium, phosphorus, potassium, sodium and magnesium. The remaining minerals are called trace elements. The generally accepted trace elements are iron, chlorine, cobalt, copper, zinc, manganese, molybdenum, iodine, selenium and bromine, and there is some evidence for more. Minerals serve structural, catalytic and regulatory roles, and both deficiency and excess can cause disease.
The four organogenic elements carbon, hydrogen, oxygen and nitrogen make up about 96% of the human body by weight and are usually not considered mineral nutrients. In nutrition the term mineral more generally refers to all other functional and structural elements found in living organisms. Plants obtain minerals from soil, animals ingest plants and move minerals up the food chain, and larger organisms may consume soil or use salt licks to obtain minerals.
Although mineral and element are often used synonymously, minerals are bioavailable only to the extent that they can be absorbed. To be absorbed they must be soluble or readily extractable by the consuming organism. Molybdenum is an essential mineral, but metallic molybdenum has no nutritional value, whereas many molybdates are sources of molybdenum.
Twenty chemical elements are known to be required for human biochemical processes through structural and functional roles, and there is evidence for a few more.
By weight, oxygen, hydrogen, carbon and nitrogen are the most abundant elements in the body and make up about 96% of body weight. Calcium accounts for 920 to 1200 grams of adult body weight, with 99% in bones and teeth, or about 1.5% of body weight. Phosphorus is about two thirds of the calcium amount and about 1% of body weight. The other major minerals, potassium, sodium, chlorine, sulfur and magnesium, make up only about 0.85% of body weight. Together these eleven elements, hydrogen, carbon, nitrogen, oxygen, calcium, phosphorus, potassium, sodium, chlorine, sulfur and magnesium, account for 99.85% of the body. The remaining approximately 18 ultratrace elements account for only 0.15%, or about one hundred grams in an average person.
Opinions differ on the essentiality of various ultratrace elements in humans and other mammals, even from the same data. Whether chromium is essential is debated, and no chromium-containing biochemical has been purified. The United States and Japan designate chromium as an essential nutrient, but the European Food Safety Authority reviewed the question in 2014 and disagrees.
Most known and suggested mineral nutrients have relatively low atomic weights and are reasonably common on land, or for sodium and iodine in the ocean. They also tend to form soluble compounds at physiological pH. Elements without such soluble compounds tend to be non-essential, such as aluminium, or at most needed in traces, such as silicon.
Minerals differ widely in function. Potassium and sodium are systemic electrolytes that regulate fluid balance, nerve impulses and muscle contraction and are closely tied to ATP use. Chlorine is needed for hydrochloric acid production in the stomach and for cell-pump function and host defence. Calcium is the main component of bones and teeth and participates in muscle contraction, heart rhythm, blood clotting and cell signalling. Phosphorus is a component of bone, cell membranes, DNA, RNA and ATP and participates in energy metabolism and acid-base buffering. Magnesium is required for ATP processing and bone and participates in hundreds of enzyme reactions.
Iron is required for haemoglobin, myoglobin and many enzymes, and deficiency causes anaemia. Zinc is a cofactor for many enzymes, including carbonic anhydrase, matrix metalloproteinases and zinc-finger proteins, and is involved in immunity, wound healing and taste. Manganese is a cofactor of superoxide dismutase and participates in antioxidant defence. Copper is involved in cytochrome oxidase, iron metabolism and connective-tissue formation. Iodine is a component of thyroid hormones, selenium is a component of glutathione peroxidase and other antioxidant enzymes, and molybdenum is a cofactor of xanthine oxidase and sulfite oxidase.
Recommended intakes vary with age, sex, physiological state and regional guidance. The United States, the European Union and Japan set recommended dietary allowances, adequate intakes and tolerable upper intake levels. The upper level is the highest long-term daily intake unlikely to cause health risk, and higher intakes may produce adverse effects.
Dietitians generally recommend obtaining minerals from foods rich in the element of interest. Elements may be naturally present, as calcium in dairy milk, or added, as calcium-fortified orange juice or iodine-fortified salt. Supplements may contain several elements as compounds, combinations of vitamins and minerals, or a single element as a compound, such as calcium carbonate, calcium citrate, magnesium oxide, ferrous sulfate or iron bis-glycinate.
The dietary focus on chemical elements reflects the need to support metabolic reactions with required elemental components. Adequate intake of certain elements is required for optimal health. Diet can meet all requirements, but supplements can be used when recommendations are not met, for example in a diet low in dairy products that does not supply enough calcium.
The list of minerals required by plants is similar to that for animals. Both use very similar enzymes, although differences exist. Legumes contain molybdenum-containing nitrogenase, which animals lack, and many animals rely on haemoglobin iron for oxygen transport, whereas plants do not. Fertilizers are often tailored to mineral deficiencies in particular soils, such as molybdenum, manganese or zinc deficiency.
Plants absorb minerals from soil, and soil pH, organic matter, clay minerals and redox conditions affect element availability. Molybdenum availability decreases in acidic soils, while iron, zinc and manganese availability decreases in calcareous soils. Mineral management in agriculture therefore involves soil amendment and rotation as well as fertilization.
The gap between recommended intake and the safe upper limit can be small. For calcium, the U.S. Food and Drug Administration sets a recommended intake of 1,200 mg per day for adults over 70 and an upper limit of 2,000 mg per day. The European Union also sets recommended amounts and upper limits that are not always in accord with the United States. Japan sets the upper limit for iodine at 3,000 μg, compared with 1,100 μg in the United States and 600 μg in the European Union.
Magnesium appears anomalous because the recommended intake for adult men is 420 mg per day and for women 350 mg per day, while the upper limit is 350 mg. The upper limit applies to taking more than 350 mg of magnesium at once as a dietary supplement, which may cause diarrhoea. Magnesium-rich foods do not cause this problem.
Risks of mineral supplements also include excessive intake, drug interactions, contamination and misuse. Excessive iron can cause gastrointestinal injury and iron overload, and excess vitamin A and D can be toxic. Pregnant women, children, older adults and people with chronic disease should use supplements only on medical or dietetic advice.
Many ultratrace elements have been suggested as essential, but such claims are usually unconfirmed. Definitive evidence of efficacy comes from characterising a biomolecule containing the element with an identifiable and testable function. One problem is that some elements are innocuous at low concentrations and pervasive, such as silicon and nickel, so proof of efficacy is lacking because deficiency states are difficult to reproduce.
Some elements were once thought to have roles of unknown biochemical nature, but the evidence has not always been strong. Arsenic was once thought probably essential in mammals but appears to be used only by microbes. Chromium was long thought essential based on rodent models and proposed to be involved in glucose and lipid metabolism, but more recent studies have called this into question. Boron is essential to plants but not humans, although depletion-repletion studies showed benefits to bone and brain health.
Non-essential elements can appear in the body when they are chemically similar to essential elements, such as rubidium and caesium replacing sodium, so essentiality is not the same as uptake by a biological system.
Animals and microorganisms use diverse ions to mineralise structures in a process called biomineralisation, constructing bones, seashells, eggshells, exoskeletons and mollusc shells. Bacteria can act on metals to catalyse mineral dissolution and precipitation and thereby participate in mineral nutrient cycling.
Mineral nutrients are recycled by bacteria distributed throughout soils, oceans, freshwater, groundwater and glacier meltwater. Bacteria absorb dissolved organic matter containing minerals as they scavenge phytoplankton blooms. Mineral nutrients pass through the marine food chain from bacteria and phytoplankton to flagellates and zooplankton, which are then eaten by other marine life. In terrestrial ecosystems, fungi play a similar role, mobilising minerals from matter inaccessible to other organisms and transporting the nutrients to local ecosystems.
Mineral ecology combines mineralogy, microbiology and ecosystem research and examines how minerals affect biodiversity, ecological processes and global element cycles. The field is important for understanding soil fertility, ocean productivity and climate feedbacks.