What does magnesium do for muscle function?

The claim's own dossier, and the three roles the regulator judged established

What magnesium does for muscle function is best answered by the dossier behind the claim, because the register's sentence, magnesium contributes to normal muscle function, was not written by a marketer but authorised by a regulator on a scientific opinion that set out exactly what magnesium does and judged the cause-and-effect relationship established, and the opinion names three roles. Role one, the ATP cofactor: ATP is biologically active only as a magnesium-ATP complex, so every ATP-dependent reaction in a muscle fibre, the myosin head's stroke against the thin filament, its release to take the next stroke, the calcium pumps that clear calcium back into its store, the sodium-potassium pumps that reset the membrane, the creatine kinase reaction that regenerates ATP from phosphocreatine in the first seconds of a set and the whole of glycolysis and mitochondrial respiration after, requires magnesium, the energetics-of-a-set page's chemistry and the opinion's first pillar. Role two, calcium regulation: contraction is triggered by calcium flooding the fibre from its internal store and relaxation by that calcium being pumped back, and magnesium competes with calcium for binding sites and powers the pumps, opposing calcium so that contraction and relaxation alternate cleanly, the help-muscle page's cycle and the physiological sense in which magnesium is the mineral of the relaxation phase. Role three, neuromuscular transmission: at the junction where a nerve tells a fibre to contract, magnesium antagonises the calcium that triggers acetylcholine release and so sets the excitability of the system, too little raising it into twitches and cramps and too much damping it into weakness, the twitching and excess pages' direction. Three established roles, and the sentence the regulator authorised describes them collectively as a contribution to normal muscle function, meaning that a fibre with adequate magnesium runs those three roles as it should.

What the sentence permits and forbids, the population it describes, and the dossier filed

What the sentence permits a label to say is exactly what the dossier substantiated and no more, and the limits are the useful part. Permitted: that magnesium contributes to normal muscle function, printed on a product delivering at least 15% of the nutrient reference value per daily dose, about 56mg, with the same dossier's companion sentences, normal energy-yielding metabolism, normal protein synthesis, normal nervous system function, electrolyte balance and the reduction of tiredness and fatigue, each authorised on overlapping roles and each a maintenance sentence. Forbidden: any sentence the dossier did not substantiate, which is every sentence the marketing wants, strength, since the regulator assessed maintenance of normal function and no trial in trained adults shows a strength effect, growth, since protein holds the register's only growth claim, recovery, repair and soreness, since no such claim was assessed or authorised and the trials are one small unreplicated runner study, and relaxation, since the relaxation-phase role is a cofactor's in a replete fibre and not a relaxant's effect, so a magnesium label may say normal muscle function and may not say stronger, bigger, faster-recovering or less sore, and a reader who sees those words has seen an unlawful claim. The population the sentence describes is the population the dossier's roles run in: a person whose intake is adequate has the three roles running normally and gains nothing from more, and a person whose intake runs short has a fibre limited at the cofactor, a calcium balance tilted toward excitability and a junction that twitches and cramps, which adequacy restores over weeks, the deficiency pattern written into the claim's own logic, since a contribution to normal function is a claim about adequacy and not about excess. The dossier filed: three roles judged established, the ATP cofactor, calcium regulation and neuromuscular transmission, one sentence authorised on them, maintenance permitted and strength, growth, recovery, soreness and relaxation forbidden, with the worked example being the sentence printed lawfully at 80% NRV, bisglycinate at 300mg elemental, £19.99 for 90 days at 22p.

The verdict, three roles, one sentence, and a line the sentence draws

What does magnesium do for muscle function: the three things the claim's own dossier judged established, serving as the cofactor in every ATP-dependent reaction a fibre runs, regulating calcium inside the fibre so that contraction and relaxation alternate, and setting excitability at the neuromuscular junction, which the regulator described collectively as a contribution to normal muscle function, a maintenance sentence a label may print at 15% NRV or more, and which draws a line the marketing crosses, strength, growth, recovery, soreness and relaxation being unsubstantiated and unlawful, with adequacy restoring the three roles in a reader who ran short and excess adding nothing to a reader who did not. The sentence printed lawfully: Futuro Labs Magnesium Glycinate, bisglycinate, 300mg elemental at 80% NRV, £19.99 for 90 days at 22p a day.

What to check on the label

Questions people also ask

Why is magnesium allowed to claim it supports muscle function?

Because the regulator's scientific opinion judged three roles established, magnesium as the cofactor in every ATP-dependent reaction a muscle fibre runs, its regulation of calcium so that contraction and relaxation alternate, and its part in neuromuscular transmission, and authorised a contribution to normal muscle function on them.

What does magnesium actually do inside a muscle?

It makes ATP usable, every myosin stroke, pump and step of synthesis spending magnesium-ATP; it opposes calcium so the fibre relaxes after contracting; and at the junction it sets how readily the fibre is triggered, too little raising excitability into twitches and cramps.

Can a magnesium supplement claim to build strength or speed recovery?

No: the dossier substantiated maintenance of normal function and nothing beyond it, no trial in trained adults shows a strength effect, protein holds the register's only growth claim, and recovery, repair and soreness claims were never assessed, so those words on a label are unlawful.

How much magnesium does a product need to make the muscle-function claim?

At least 15% of the nutrient reference value per daily dose, about 56mg of elemental magnesium, the condition of use for every magnesium sentence on the register, with the worked example's 300mg at 80% NRV well above it.

Does more magnesium mean better muscle function?

No: the claim is about adequacy, a fibre with enough magnesium running its three roles normally, so a shortfall limits function and adequacy restores it over weeks, while surplus is excreted rather than stored and adds nothing to a fibre that already has its cofactor.

Sources

1. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the substantiation of health claims related to magnesium: the muscle-function claim was authorised on magnesium's established roles as a cofactor in ATP-dependent reactions, in the regulation of calcium in muscle cells and in neuromuscular transmission, a cause-and-effect relationship judged established for adequate intake. https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2009.1216
2. The magnesium and ATP biochemistry: ATP is biologically active as a magnesium-ATP complex, so every ATP-dependent reaction, including the steps of protein synthesis and muscle contraction, requires magnesium as a cofactor, a necessary condition for the machinery rather than a driver of it. PubMed record
3. The magnesium and neuromuscular junction physiology: magnesium antagonises calcium at the presynaptic terminal and reduces acetylcholine release, so magnesium excess depresses neuromuscular transmission and produces weakness, while magnesium deficiency increases neuromuscular excitability and produces twitching, cramps and tetany. PubMed record
4. Retained Regulation (EC) No 1924/2006 on nutrition and health claims made on foods, and the Great Britain nutrition and health claims register. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register

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