A mineral is an element, so nothing living has ever made one. In a body it works as a charged particle — and what it does, along with how much of it arrives, follows from that charge.
~11 min read
Every other nutrient in this section was assembled by something. A vitamin is a molecule a living thing built from carbon, hydrogen and oxygen, and heat or light can undo it. A mineral cannot be built and cannot be taken apart. A mineral is an element — one entry on the periodic table — and nothing living has ever made one.
Every calcium atom in your bones came out of rock. Weathering frees it into soil, water carries it in solution, a root takes it up, and you eat that plant or something that did. There is no other route in, so the only question about a mineral is where it is.
That changes what "essential" is doing. Humans lack one working enzyme in the pathway to vitamin C, and that missing step is what puts a vitamin on the list. No enzyme has ever been missing for magnesium. Magnesium is on the list because it is an element, and only a star makes an element.
One consequence sits on your own shelf. A mineral is held in an ionic lattice, and a lattice is not volatile, so steam distillation leaves every one of them in the plant material. There is no calcium in a bottle of lavender. This lesson is the half of plant chemistry that stays in the pot.
In a body a mineral is never a metal. It is an ion: an atom that has given electrons away or taken them on, and so carries a charge. Sodium hands over its one loose outer electron and becomes Na⁺; calcium hands over two and becomes Ca²⁺. Chemical bonding covers the transfer; this is what a body does with the result.
An ion is not a small piece of metal
Elemental magnesium is a soft grey metal that burns with a white flame and reacts with water. The magnesium in your blood is Mg²⁺, a charged particle wrapped in water, with none of those properties. The label names the element. The ion does the work.
A protein picking one ion out of a crowded cell has little to go on: no molecule, so no functional group to read. It has two measurements: the charge the ion carries, and its size. That is enough — sodium and potassium both carry one positive charge, and thirty-six picometres of difference in radius is what lets a channel admit one and refuse the other.
Diagram to come
A single scatter plot, charge on one axis and ionic radius on the other, with each ion drawn as a circle whose SIZE is its actual radius to scale rather than a uniform marker. Positives on the upper half, the two negatives below a dividing line. Sodium and potassium must sit at the same charge with visibly different circle sizes; magnesium and calcium likewise, one small and one noticeably larger, both at double charge; zinc drawn almost exactly the size of magnesium, to make the point that similar ions are hard to tell apart; iron shown twice, at +2 and at +3, joined by a small double arrow labelled as the switch, with the +3 circle visibly the smaller. Radii in picometres printed beside each circle. No bodies, no cells, no food — this figure is chemistry only, and its job is to make "charge and size are all a binding site can measure" something the reader sees rather than reads.
| Ion | Charge | What the charge is used for |
|---|---|---|
| Sodium — Na⁺ | +1 | Held high outside. Its inward rush is the first half of a nerve signal. |
| Potassium — K⁺ | +1 | Held high inside. Its outward flow restores the resting state. |
| Calcium — Ca²⁺ | +2 | Kept almost absent inside, so admitting a little is an unmistakable instruction. |
| Magnesium — Mg²⁺ | +2 | Small and strongly charged: grips negative phosphates and holds them in place. |
| Iron — Fe²⁺ / Fe³⁺ | +2 or +3 | Carries single electrons by switching between the two. Holds oxygen in haemoglobin. |
| Zinc — Zn²⁺ | +2 | Fixed at +2, so it holds a protein in shape without reacting. |
| Chloride — Cl⁻ | −1 | The commonest negative ion. Balances the positives, travels with sodium. |
| Phosphate — PO₄³⁻ | −3 | Heavily negative: what makes ATP a store, and what binds calcium into bone. |
A nerve is not a wire and a muscle is not a motor. Both run on a difference in ion concentration, held across a membrane at constant cost and spent in bursts.
Inside a resting cell, potassium sits at roughly 140 millimoles per litre and sodium at 10 to 15. Just outside, the figures are nearly reversed: sodium about 140, potassium 4 to 5. A pump holds that arrangement, moving three sodium out for every two potassium in and spending one ATP each cycle. Three positives leave and two arrive, so the inside is left about seventy millivolts negative. Holding that separation across every membrane you own is commonly put at a fifth to a third of a resting cell’s energy budget.
A signal is the arrangement failing, briefly and on purpose. A channel opens, sodium pours down its gradient, the interior swings positive within a millisecond; potassium channels open, potassium leaves, the voltage falls back, and the pump restores the separation behind it. Nothing travels along the nerve — what moves is the position of a collapse, and the nervous system is built on it end to end. It is also why almost all the body’s potassium sits inside cells, where the pump put it.
Calcium is used differently, and the reason is contrast. A resting cell holds free calcium inside at around 100 nanomoles per litre against one to two millimoles outside — roughly ten thousandfold, maintained by pumps that never stop. That near-silence is expensive, and it buys precision: admit a little and the change is enormous in proportion, so it cannot be mistaken for background. It is how a muscle is told to contract. The same ion is locked into the mineral phase of bone, which is why it runs through the musculoskeletal system too.
Diagram to come
One cell membrane drawn as a horizontal double layer across the figure, inside below and outside above. Sodium and potassium drawn as labelled circles whose density on each side matches the real ratio, so the reversal reads at a glance — crowded sodium above, crowded potassium below. Mid-membrane, the pump drawn as a protein spanning it, three sodium ions leaving and two potassium entering on one cycle, one ATP consumed beside it. To the right, a voltage scale marked at the resting value. Below, a separate inset for calcium: the same membrane with the outside dense in calcium and the inside almost empty, the emptiness annotated with the real ratio, and one channel admitting a few ions into it. A reader should finish able to say why calcium works as a message and sodium as a current.
The other half of the work happens with the ion held still. A large share of all proteins — commonly put at about a third — cannot function without a metal ion bound into them, holding the structure together or sitting where the chemistry happens. Enzymes and cofactors takes that apart; what each ion brings to it is its charge.
Magnesium — the clamp
Two positive charges inside a radius of 72 picometres — a concentrated pull that grips strongly negative things. ATP carries three phosphate groups in a row, all negatively charged and all repelling one another; Mg²⁺ sits between two of them, cancels the repulsion and folds the molecule into the shape an enzyme can use. Nearly all the ATP in a cell is magnesium-bound, which is why magnesium appears in reaction after reaction without being the subject of any. It is not a participant. It is a vice.
Iron — the electron carrier
Iron is useful because it does not settle. Fe²⁺ gives up one electron to become Fe³⁺ and takes it back, endlessly: a way of moving single electrons about, and the basis of the cytochromes that pass electrons down the chain in a mitochondrion. Inside a flat ring called haem the same iron binds oxygen instead: one iron per haem, four haems per haemoglobin. An adult holds three to four grams of iron, most of it in that one job.
Zinc — the structural atom
Zinc is the opposite choice. Fixed at +2 and unwilling to switch, it sits in a protein indefinitely without starting any chemistry of its own, and that inertness is the qualification. In a zinc finger the ion pulls a loop of protein chain together at the angle that fits the groove of a DNA double helix. Thousands of human proteins hold a zinc atom doing nothing but holding a shape.
Two more are used more directly still. Selenium is built into an amino acid — selenocysteine, cysteine with its sulphur swapped for selenium, the element directly below sulphur — and that is the active centre of glutathione peroxidase, one of the enzymes the body uses for its own oxidative chemistry. Iodine is simply part of a formula: T4 carries four iodine atoms, T3 carries three.
Magnesium and calcium both carry two charges and differ in radius by 28 picometres; zinc and magnesium differ by two. Yet a magnesium site will not take calcium, and a zinc site will not take magnesium. Three things separate them.
A bare mineral ion is poorly taken up, and the reason is chemistry rather than biology being awkward. Here is where the word after the mineral name starts to matter.
Follow a magnesium ion out of a plain inorganic salt. In the stomach, at a pH between 1.5 and 3, acid pulls the salt apart and frees it. The contents move into the small intestine, where the pH climbs to around 6 or 7 — and a free doubly charged metal ion in near-neutral water does not stay free. It associates with hydroxide, with phosphate, with whatever is passing, and much of it goes insoluble. What survives has to find a transporter, because a hydrated, charged particle cannot cross a fatty membrane unaided.
Chelation is the answer, and it is ordinary coordination chemistry rather than a marketing word. A chelating ligand has two or more atoms able to donate a lone pair to the same metal ion, so it closes around the ion in a ring rather than at one point — the word is Greek, for a crab’s claw. Glycine donates through the nitrogen of its amino group and an oxygen of its carboxyl group: two points, one ring. Magnesium bisglycinate is one magnesium ion with two glycines wrapped round it, a small, largely neutral molecule with its charge buried inside.
A chelate therefore stays in solution across the swing in acidity and has far less exposed charge to precipitate. The size of that advantage varies by mineral and by the form compared against; anyone quoting one precise multiplier has rounded off much disagreement. Absorption and bioavailability follows the whole route.
Diagram to come
Two lanes running left to right along the same stretch of gut, one above the other so the comparison is unavoidable. Both start in the stomach, marked with its pH, pass into the small intestine, marked with its higher pH, and end at a section of intestinal wall with its microvilli. Top lane, the bare ion: a metal ion shedding its salt partner in the acid, then wearing a visible shell of water molecules, then most of the ions clumping with passing hydroxide and phosphate into grey precipitate that goes no further, with one or two reaching a transporter protein in the wall and queueing at it. Bottom lane, the chelate: the same ion held inside a two-armed glycine ring that comes apart at neither pH, travelling intact, crossing at the wall by a route away from the crowded transporter. The charge must be drawn visible on the bare ion and visibly enclosed on the chelated one — that single contrast is the whole figure.
| What the label says | What that means for the ion |
|---|---|
| Oxide, carbonate, sulphate, chloride | An inorganic salt. Highest percentage of the element by weight, but it must come free as a bare ion first, and oxide and carbonate lean on stomach acid. |
| Citrate, malate, lactate, gluconate | An organic acid salt and a partial chelate; citrate holds at three points. Lower percentage by weight, and stays soluble as the pH rises. |
| Glycinate, bisglycinate, amino acid chelate | A full chelate, the ion enclosed in a ring of one or two amino acids. Lowest percentage by weight, least exposed charge in the gut. |
Elemental weight and absorbed weight are two different numbers
Magnesium oxide is about 60 per cent magnesium by weight, because the oxide partner is tiny. Magnesium bisglycinate is around 14 per cent, because two glycines are heavy. The oxide wins that comparison and loses the one that matters: the proportion of an element in a compound says nothing about how much crosses the gut wall. A panel that names no form at all has told you less than it seems, and reading a supplement label does the arithmetic on a real one.
Selecting on charge and radius cuts both ways. A transporter built to carry Fe²⁺ across the intestinal wall will also carry zinc, manganese and copper, because to a binding site those are doubly charged ions of roughly the right size. Similar ions therefore compete for one route: the unavoidable cost of measuring only two things.
Plants bind minerals too, and the strongest binder in an ordinary diet is phytate: a ring of six carbons carrying six phosphate groups, the way a seed stores what it needs to germinate. At the pH of the gut those phosphates carry up to twelve negative charges between them, making phytate a very effective chelator of anything positive — and unlike a glycinate it does not let go at the intestinal wall, so what it holds passes straight through. Soaking, sprouting, fermenting and leavening all reduce it, each giving the enzyme phytase time to take the phosphates off. Oxalate binds calcium the same way.
Which leaves the word everyone uses and few define. An electrolyte is a substance that dissolves into ions and therefore conducts. The electrolytes in you are the ions already named — sodium, potassium, chloride, calcium, magnesium — dissolved in blood and in the fluid around cells. Their concentrations decide where water sits, since water crosses a membrane toward whichever side holds more dissolved particles. Sweat is water with ions in it, sodium commonly 20 to 80 millimoles per litre, so heavy sweating takes both and water alone returns one. There is no separate class of substance called an electrolyte. There is the ion, in solution, doing what a charge does.
Major and trace is a statement about quantity and nothing else. An adult holds around 1.2 kilograms of calcium. Against that, total body selenium is 13 to 20 milligrams and total body iodine 15 to 20 — amounts you could lose in a spoon. A body uses so little because each sits at the active centre of a small number of proteins, and a protein needs one atom, not a supply.
Which is why the window is tight. When a body’s whole content of an element is measured in milligrams there is no store to buffer in either direction, so one small absolute amount is the difference between short and surplus.
The transition metals add a second reason. An ion that carries electrons back and forth is a catalyst, and a catalyst in the wrong place catalyses the wrong thing: in a beaker, iron in solution with hydrogen peroxide generates hydroxyl radicals — textbook inorganic chemistry, and not a statement about anything happening in a person. So the body leaves almost none of it loose. Iron travels bound to transferrin and is stored inside ferritin, a hollow protein shell holding several thousand atoms. A useful ion is one kept exactly where it is wanted.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. A dietary supplement does not replace a varied diet, and nothing here replaces professional medical care. If you are pregnant, nursing, under medical care or taking medication, speak to your healthcare practitioner before using any supplement. Product availability and label reference figures differ from market to market.
Two lessons, two properties. A vitamin is read by asking whether it is polar; a mineral by asking what charge it carries and how large it is. Between them that is most of how a body handles a micronutrient. What comes next is what the ion does once bound — and almost every mineral here spends its working life inside a protein, as does most of the B group. One mechanism, not two.
Lesson 15 of 18 · Science