The magnesium capsule is not magnesium: it is magnesium plus a form that decides whether the mineral will cross the intestinal barrier. Magnesium oxide is cheap and poorly absorbed; magnesium bisglycinate costs more and absorbs well. Food supplements are the market where price, form and marketing do not say the same thing: what counts is not the number of milligrams but what reaches the blood.
Between food and medicine: a grey zone
The food supplement occupies a place between two statuses: neither food (it is concentrated, isolated, dosed) nor medicine (it has not passed the efficacy trials of a drug). It is a health product without the medicine’s framework: its sale is free, its efficacy is not guaranteed by a patient leaflet, and its quality depends on the manufacturer.
This grey zone has two consequences. The first: variability is enormous, and two products bearing the same name are not worth the same. The second: responsibility shifts to the consumer, who must know how to read the form, the dose, the label, the interaction. The supplement is the tool of the documented deficit; used “just in case”, it becomes an expensive placebo or a needless risk.
Galenic forms: what absorbs and what passes through
The same substance exists in several chemical forms, and the form decides the bioavailability. Magnesium is the textbook case:
| Substance | Weak form | Absorbable form | Note | |
|---|---|---|---|---|
| Magnesium | Oxide, hydroxide | Bisglycinate, citrate, taurate | The laxative oxide is poorly absorbed | Bisglycinate is the reference |
| Iron | Ferrous sulphate | Ferrous bisglycinate, liposomal iron | Sulphate irritates, bisglycinate less so | Vitamin C aids absorption |
| Calcium | Carbonate | Citrate | Carbonate requires gastric acid | Citrate absorbs without a meal |
| Zinc | Oxide | Bisglycinate, picolinate, citrate | Oxide is poorly absorbed | Excess zinc depletes copper |
| Vitamin B12 | Cyanocobalamin | Methylcobalamin, hydroxocobalamin | Cyano is stable, methyl is active | Sublingual if absorption is difficult |
| Vitamin D | D2 (ergocalciferol) | D3 (cholecalciferol) | D3 is more effective than D2 | Fat-soluble: take with fats |
The form, its bioavailability, its use
The reading rule: organic forms (citrates, glycinates, picolinates, liposomal forms) absorb better than mineral forms (oxides, carbonates, sulphates). Price follows bioavailability: bisglycinate costs more than oxide because it reaches the blood rather than the stool.
Quality labels: what guarantees
The supplement has no medicine leaflet, but it has labels that certify manufacturing quality. The landmarks:
- GMP (Good Manufacturing Practice): the baseline, controlled production. Present on serious brands.
- NSF International, USP, Informed Sport: independent certifications that verify actual composition (what is written is inside) and the absence of contaminants. Athletes know Informed Sport.
- Organic label: guarantees the origin of plant extracts, not bioavailability or efficacy.
- Form transparency: a good supplement displays the chemical form (bisglycinate, not “magnesium” alone) and the elemental dose (300 mg of elemental magnesium, not 3000 mg of bisglycinate).
The absence of a label does not condemn the product, but it shifts the burden of proof to the consumer. Without certification, the brand, the form and the dosage are the only clues.
Interactions: when the supplement meets the medicine
The supplement is not inert: it interacts with medicines and with other supplements. The documented interactions:
- St John’s wort: the most interactive of all, it induces hepatic CYP3A4 and speeds the elimination of dozens of medicines (contraceptives, anticoagulants, immunosuppressants, antidepressants). It is the most dangerous interaction on the market.
- Vitamin K and anticoagulants: vitamin K (green vegetables, supplements) antagonises warfarin-type drugs; the dose must be stable, not necessarily zero.
- Iron and calcium: they compete for absorption; take them separately.
- Zinc and copper: excess zinc depletes copper; prolonged supplementation requires the balance.
- Omega-3 and anticoagulants: at high doses omega-3 thin the blood; flag it to the doctor when a treatment is running.
The safety rule: every supplement is declared to the doctor and pharmacist while a treatment is ongoing. The “natural” plant is not interaction-free: St John’s wort is the best-documented counter-example.
The documented-deficiency rule: when to supplement
A supplement has its place when three conditions meet: a documented deficit (laboratory result or clear clinical picture), an impossibility of correcting it through diet alone (insufficient intake, malabsorption, increased need), and a suitable form and dose. The situations where supplementation is documented: vitamin D in winter, B12 in strict vegans, low ferritin in women, folic acid preconception, magnesium in stressed terrains that eat too few greens.
The “just in case” supplement, with no deficit, is the opposite of rational supplementation: it costs, it can interact, and it corrects nothing. Discernment is not taking or refusing supplements; it is taking them when the deficit is there, in the right form, at the right dose, for the right duration.
The TCM reading: the concentrate that demands a Spleen
Chinese dietetics reads the supplement as a concentrated food: it lacks the matrix of the whole plant, it carries the isolated substance. And the Spleen must transform what enters: a concentrated substance on a weak Spleen does not transform, it stagnates or it passes through. Spleen deficiency is the terrain that absorbs everything poorly, supplements included: correcting the Spleen terrain is the precondition for any supplementation that intends to arrive.
TCM adds the nuance of the whole: the food is the plant with its Qi, its flavour, the matrix that modulates; the supplement is the isolated substance, effective on a deficit but without the context. Food first, the supplement when food no longer suffices: the rule Chinese dietetics has always held. The articles on vitamins and minerals and on vegan supplementation show the two faces: documented nutrients, and the case where supplementation is compulsory.
Frequently asked questions about food supplements
Which supplements are genuinely useful?
Those that correct a documented deficit: vitamin D in winter for most people, B12 in strict vegans, low ferritin in women, folic acid preconception, magnesium in deficient terrains. The rest depends on the terrain: a useful supplement is one that biology or the clinical picture justifies.
How do you judge quality?
Three landmarks: the displayed form (bisglycinate, citrate, organic forms rather than oxides), the manufacturing label (GMP at minimum, NSF or USP for independent certification), and a clear elemental dose (the quantity of mineral, not of salt). Without these markers, the burden of proof shifts to the consumer.
Are supplements dangerous?
Interactions and megadoses are: St John’s wort with contraceptives and anticoagulants, beta-carotene in smokers, iron without deficiency. At a reasonable dose and for a documented deficit, the risk is low. The danger is not the supplement; it is use without discernment.
Can you supplement without medical advice?
For simple supplements (vitamin D, magnesium), yes, within the stated doses. But as soon as a medication is running, or a severe deficit is suspected, medical or pharmacist advice is required: interactions are real and megadoses carry documented risks.
Should supplements be taken permanently?
No: the supplement corrects a punctual deficit, it is taken for a duration and stopped when the deficit is corrected. Permanent supplementations (D in winter, vegan B12) have their indication, but most supplements are corrections, not daily foundations.
Discernment replaces habit
Food supplements are tools, not habits: useful on a documented deficit, useless or risky “just in case”. The form decides absorption, the label decides trust, the dose decides risk, and the duration decides relevance. The TCM reading adds its piece: the concentrated supplement demands a Spleen that transforms, and it lacks the matrix of the whole food. Discernment is not taking or refusing: it is taking when indicated, in the right form, for the right reason.
In the Yin Shi app, the cards for foods rich in iron, zinc, magnesium and vitamins show their content and their favourable pairings: lentils and seeds tick the boxes of the food that corrects, the capsule those of the punctual fix.
To go further: the vitamins and minerals guide, vegan supplementation, functional nutrition, heavy metals and competing minerals, and TCM phytotherapy and micronutrition.
To go further
Yin Shi ecosystem resources directly related to this article.