Minerals
Essential inorganic elements that the body cannot make and must get from food, involved in bone structure, fluid balance, muscle contraction and hundreds of enzyme reactions.
Minerals fall into two groups according to the amounts needed. The major minerals (calcium, phosphorus, magnesium, potassium, sodium, chloride, sulphur) are counted in hundreds of milligrams or even grams a day. The trace elements (iron, zinc, copper, iodine, selenium, manganese, chromium, molybdenum) are needed only in tiny amounts, but a deficiency has just as clear consequences.
Unlike vitamins, minerals are indestructible: neither heat nor light breaks them down. They are, however, soluble in water, and a significant share ends up in the cooking water. Steaming vegetables, or reusing the cooking liquid, really does change what a meal provides.
What matters is not the content but the absorption. A food rich in iron or calcium delivers only a fraction of it, which is the question of bioavailability. The phytates in wholegrains and pulses, the oxalates in spinach or rhubarb, and the tannins in tea and coffee slow the absorption of minerals. Conversely, vitamin C clearly improves the absorption of plant-based iron.
Minerals also compete with each other: at high doses, zinc interferes with copper absorption and calcium with iron. This is a concrete argument against supplements taken at random doses, and in favour of a varied diet where intakes balance out naturally.