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Minerals are inorganic micronutrients classified as macrominerals (required >100 mg/day: calcium, phosphorus, magnesium, sodium, potassium, chloride, sulfur) and trace elements (required <100 mg/day: iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium, molybdenum). They serve structural roles (calcium and phosphorus in bone), regulatory roles (sodium and potassium in membrane potential), and catalytic roles (zinc as a cofactor in >300 enzymes). Bioavailability varies widely depending on food source, food matrix, and enhancing or inhibiting dietary factors.
Focus on the five most clinically significant minerals (calcium, iron, zinc, iodine, sodium) and trace their absorption pathways. Compare dietary sources and bioavailability of heme versus non-heme iron to understand why iron deficiency is the world's most common micronutrient deficiency.
Minerals are inorganic elements that the body cannot synthesize and must obtain from food. Unlike macronutrients, which are burned for energy or used as building blocks for organic molecules, minerals remain as ions and atoms — performing their functions through electrical charge, structural bonding, or catalytic activity. The division into macrominerals and trace elements is purely quantitative: macrominerals are needed in gram-scale amounts daily, while trace elements are needed in milligram or microgram quantities. But smaller requirement does not mean less important — iodine is needed in only about 150 micrograms per day, yet iodine deficiency is the leading preventable cause of intellectual disability worldwide.
Minerals serve three categories of function. First, structural: calcium and phosphorus together form hydroxyapatite, the crystalline mineral that gives bone and teeth their hardness and rigidity — 99% of the body's calcium is in bone, serving as both a structural reservoir and a blood calcium buffer. Second, regulatory: sodium and potassium are the principal ions controlling membrane potential, nerve impulse transmission, and fluid balance across cells (concepts you encountered in the fluid balance and electrolytes topic). Their gradients, maintained by Na⁺/K⁺-ATPase pumps, power much of cellular signaling. Third, catalytic: zinc is a cofactor in over 300 enzymes, including those involved in DNA synthesis, immune function, and wound healing. Iron is the functional core of hemoglobin and myoglobin, carrying and releasing oxygen. Without the right mineral in the right enzyme's active site, that enzyme simply cannot function.
Bioavailability — the fraction of a mineral that is actually absorbed and used — varies enormously and is not predictable from the food's mineral content alone. Heme iron (from animal hemoglobin and myoglobin) is absorbed at roughly 15–35% efficiency regardless of body status. Non-heme iron (from plant foods, fortified products, and supplements) is absorbed at only 2–20%, but this rate is highly sensitive to enhancers (vitamin C, which reduces Fe³⁺ to the absorbable Fe²⁺ form) and inhibitors (phytic acid in grains, tannins in tea, calcium at high doses). This is why iron deficiency is the world's most common micronutrient deficiency despite iron being abundant in plant foods — absorption, not intake, is the limiting factor.
A critical feature of many trace elements is the U-shaped dose-response curve: too little causes deficiency disease, but too much is toxic. Selenium is a clear example — required for glutathione peroxidase (an antioxidant enzyme) and thyroid hormone metabolism, but toxic above about 400 micrograms per day, causing hair loss, nail brittleness, and neurological effects. Supplementing selenium "to boost immunity" beyond the recommended intake does not produce additional benefit and increases risk of adverse outcomes. The same logic applies to zinc, iodine, and fluoride. More is not better; optimal is within a narrow range.
Bioavailability interactions mean that diet composition affects mineral status as much as mineral content. Consuming calcium and iron together in the same meal reduces iron absorption because calcium competes for the same intestinal transporter. Vitamin D dramatically increases calcium absorption by upregulating the intestinal transport protein calbindin — which is why calcium supplements without vitamin D are less effective. Phytic acid (from whole grains and legumes) chelates iron, zinc, and calcium, reducing their absorption — which is partly why fermentation and soaking of legumes, which reduce phytate content, have been nutritionally important food preparation techniques across cultures.