Dietary Minerals: Why Your Body Needs Metals

Nutrition labels list minerals like calcium, iron and potassium, but chemically these are elements, many of them metals, taken in as ions dissolved in food and water. Your body is built mostly from carbon, hydrogen, oxygen and nitrogen, but it can’t run without about fifteen other elements that do very specific jobs: carrying oxygen, sending nerve signals, building bones, and sitting at the heart of enzymes. This list goes through them, with the chemistry behind each.

For an overview of every element in the body, including the non-mineral ones, see elements in the human body.

Two groups: major and trace

• Major minerals (macrominerals) are needed in amounts of more than about 100 mg a day.
• Trace elements (microminerals) are needed in amounts of a few milligrams or micrograms a day.

“Trace” doesn’t mean unimportant: a lack of iodine or iron can cause serious disease.

Major minerals

1. Calcium (Ca²⁺)

• Roles: the main mineral in bones and teeth (as calcium phosphate, hydroxyapatite); needed for muscle contraction, nerve signalling, blood clotting and as a signal inside cells.
• Sources: dairy, fortified plant milks, tofu set with calcium salts, leafy greens, sardines with bones.
• Too little: weak bones (osteoporosis), and in children poor bone growth. See calcium, phosphate and bone chemistry.
• Element page: calcium

2. Phosphorus (as phosphate, PO₄³⁻)

• Roles: bone mineral alongside calcium; part of ATP, DNA, RNA and phospholipid membranes; part of the body’s pH buffering.
• Sources: almost all protein-rich foods, dairy, meat, grains; deficiency is rare.
• Element page: phosphorus

3. Potassium (K⁺)

• Roles: the main positive ion inside cells; essential for the electrical potential across cell membranes, nerve impulses and heartbeat.
• Sources: bananas, potatoes, beans, lentils, leafy greens, dried fruit.
• Too little or too much: both disturb heart rhythm. Blood potassium is tightly controlled by the kidneys.
• Element page: potassium

4. Sodium (Na⁺)

• Roles: the main positive ion outside cells; controls fluid balance and blood volume; essential for nerve impulses. The sodium–potassium pump keeps Na⁺ high outside and K⁺ high inside cells.
• Sources: salt (sodium chloride) and processed foods; most people eat far more than they need.
• Too much: raises blood pressure in many people. Health bodies commonly advise less than about 5–6 g of salt a day.
• Element page: sodium

5. Chloride (Cl⁻)

• Roles: the main negative ion outside cells, balancing sodium; part of stomach acid (HCl) (see stomach acid chemistry).
• Sources: salt.

6. Magnesium (Mg²⁺)

• Roles: needed by hundreds of enzymes, especially those that use ATP (which is bound to Mg²⁺ in cells); part of bone; muscle and nerve function. It’s also the central ion in chlorophyll (see chlorophyll).
• Sources: nuts, seeds, wholegrains, leafy greens, beans.
• Element page: magnesium

7. Sulfur

• Roles: part of the amino acids cysteine and methionine, so part of almost all proteins; disulfide bridges hold many proteins in shape.
• Sources: protein foods. Sulfur isn’t usually considered separately in diets because protein supplies enough.

Trace elements

8. Iron (Fe²⁺/Fe³⁺)

• Roles: carries oxygen in haemoglobin and myoglobin; part of cytochromes in the electron transport chain and many enzymes.
• Sources: red meat, liver, beans, lentils, fortified cereals, dark leafy greens. Vitamin C improves absorption of plant iron.
• Too little: iron-deficiency anaemia, the most common nutritional deficiency worldwide. See iron in the body.

9. Zinc (Zn²⁺)

• Roles: part of more than 300 enzymes (such as carbonic anhydrase and alcohol dehydrogenase) and of “zinc finger” proteins that bind DNA; immune function and wound healing.
• Sources: meat, shellfish (especially oysters), seeds, nuts, wholegrains.
• Element page: zinc

10. Iodine (as iodide, I⁻)

• Roles: an essential part of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which control metabolic rate and brain development.
• Sources: seafood, dairy, eggs, iodised salt.
• Too little: goitre (swollen thyroid) and, in pregnancy, impaired brain development in the baby. Salt iodisation is one of the most successful public-health measures in history.
• Element page: iodine

11. Copper (Cu⁺/Cu²⁺)

• Roles: part of cytochrome c oxidase (the final enzyme of respiration), the antioxidant enzyme superoxide dismutase, and enzymes that make connective tissue and melanin; helps iron metabolism.
• Sources: shellfish, nuts, seeds, liver, wholegrains.

12. Selenium

• Roles: built into proteins as the amino acid selenocysteine, in antioxidant enzymes (glutathione peroxidases) and enzymes that activate thyroid hormone.
• Sources: Brazil nuts (very rich; one or two a day is enough), fish, eggs, meat. Soil selenium varies widely by region.
• Too much: toxic in excess (selenosis), so the safe range is fairly narrow.

13. Manganese (Mn²⁺)

• Roles: part of several enzymes, including a form of superoxide dismutase and enzymes in carbohydrate and amino acid metabolism.
• Sources: wholegrains, nuts, tea, leafy vegetables.

14. Fluoride (F⁻)

• Roles: strengthens tooth enamel by forming fluorapatite, which resists acid attack better than hydroxyapatite. Whether it’s strictly “essential” is debated, but it clearly helps prevent tooth decay.
• Sources: fluoridated water, toothpaste, tea.

15. Chromium, molybdenum and cobalt

• Molybdenum is part of a few enzymes, such as xanthine oxidase, which help break down purines and sulfur compounds.
• Cobalt is needed only as part of vitamin B12.
• Chromium was long thought to help insulin action, but recent reviews question whether it’s truly essential.

Why metals? The chemistry

Metal ions can do things that the organic molecules of life can’t:

• carry charge as ions, creating electrical signals across membranes (Na⁺, K⁺, Ca²⁺);
• change oxidation state, carrying electrons in redox reactions (Fe, Cu, Mn, Mo; see oxidation and reduction);
• bind and activate small molecules such as O₂ and water (Fe in haemoglobin, Zn in carbonic anhydrase);
• form rigid mineral structures (Ca and phosphate in bone).

Many of these are transition metals, whose partly filled d orbitals let them switch oxidation states and bind to other molecules easily (see transition metals).

How chemists measure minerals in food

The mineral values printed on food labels come from laboratory analysis. A food sample is usually first “ashed” (heated strongly to burn off all the organic matter) or digested in concentrated acid, leaving the minerals behind as a solution of ions. The concentration of each element is then measured by instrumental methods such as atomic absorption spectroscopy or ICP-MS, which can measure dozens of elements at once down to parts per billion. For sodium and potassium, simpler flame photometry is still used. The same techniques are used to check drinking water and to monitor patients’ blood mineral levels in hospitals.

Getting the balance right

For most minerals, both too little and too much are harmful. The body controls levels through absorption in the gut, storage and excretion by the kidneys, but these systems have limits. A varied diet usually supplies what most people need; supplements are most useful for specific groups (such as iron in pregnancy or for people with diagnosed deficiency) and should be used with care.

Key takeaways

• Dietary minerals are elements, mostly taken in as ions, needed in amounts from micrograms to grams a day.
• Major minerals (Ca, P, K, Na, Cl, Mg, S) build bones, control fluid balance and carry nerve signals.
• Trace elements (Fe, Zn, I, Cu, Se, Mn, F and others) mostly work inside enzymes and hormones.
• Metals are used for their ability to carry charge, change oxidation state and bind small molecules.
• Both deficiency and excess cause disease. Explore each element’s chemistry on the elements page.