Magnesium is one of the few supplement ingredients with a substantial list of authorised health claims in Great Britain. It is also sold in a bewildering number of forms, each marketed as the one that finally works.
The thing to check first: elemental magnesium
Magnesium is never supplied on its own. It is bound to something — glycine, citric acid, oxygen — and the compound weight is not the magnesium weight.
A capsule stating “magnesium citrate 500mg” does not give you 500mg of magnesium. Depending on the form, the elemental content can be anywhere from around 10% to around 60% of the compound weight.
This is why the figure that matters is the elemental magnesium per serving, usually shown with a %NRV. A label that only gives compound weights is not telling you what you need to know. If you are comparing two products, compare the elemental figures or you are not comparing anything.
The common forms
Magnesium glycinate (bisglycinate) — bound to the amino acid glycine. Well tolerated, and the form most often chosen for evening products. Moderate elemental content.
Magnesium citrate — bound to citric acid. Good solubility. Higher doses have a laxative effect, which is either a drawback or the point depending on why you are taking it.
Magnesium malate — bound to malic acid. Often chosen for daytime formulas.
Magnesium oxide — the highest elemental content by weight and the cheapest, but poorly absorbed. Its high elemental figure makes cheap products look impressive on paper.
Magnesium taurate — bound to taurine. Less common, less studied.
What the rules let us say
Magnesium has several authorised claims on the GB register, including that it contributes to normal muscle function, to the reduction of tiredness and fatigue, to normal functioning of the nervous system, and to normal psychological function.
Those claims are conditional. A product may only carry them if it is at least a source of magnesium — meaning it provides a minimum proportion of the Nutrient Reference Value per serving. A product with a token amount does not qualify, however impressive the compound weight looks.
This is the practical reason to check the elemental figure. It determines whether the claims on the label are legitimate.
Does the form really matter?
Less than marketing suggests, and more than nothing. Absorption differences between the well-formulated organic forms — glycinate, citrate, malate — are modest. The genuinely meaningful gap is between those and cheap oxide-heavy products.
A blend of several forms is not automatically better than one good form at an adequate dose. It is a formulation choice, not a guarantee.
Before you start
Food supplements should not be used as a substitute for a varied and balanced diet or a healthy lifestyle. Do not exceed the stated daily serving. Not suitable for children. If you are pregnant, breastfeeding, taking any medication or under medical supervision, speak to your doctor or pharmacist before use.