Magnesium

Magnesium is an essential mineral and the fourth most abundant in the body, with roughly 60 per cent stored in bone. It acts as a cofactor in several hundred enzymatic reactions, including every reaction involving ATP, since ATP is biologically active bound to magnesium.

Dietary sources include green leafy vegetables, nuts, seeds, legumes and wholegrains. Population intake surveys in the UK and elsewhere consistently show a meaningful proportion of adults falling below reference intakes, which makes this one of the few supplement ingredients addressing a genuine shortfall rather than topping up sufficiency.

Form matters enormously and is the main thing distinguishing products. Magnesium oxide is cheap and contains a high percentage of elemental magnesium but is poorly absorbed, with much of it acting as a laxative. Glycinate and bisglycinate are well absorbed and gentle. Citrate is well absorbed with a mild laxative effect. Taurate and threonate are used for more specific purposes.

Magnesium's roles are structural and catalytic rather than pharmacological. It stabilises ATP, participates in DNA and protein synthesis, and is required for the enzymes involved in glycolysis and oxidative phosphorylation.

In muscle, magnesium acts as a natural calcium antagonist. Calcium influx triggers contraction; magnesium opposes it and permits relaxation. This is the physiological basis for the association between low magnesium status and cramping or muscle tension.

In the nervous system it modulates NMDA receptor activity, blocking the channel under resting conditions and thereby limiting excitatory signalling. This underpins interest in magnesium for sleep and nervous system calm, and explains why forms differing in their ability to reach the central nervous system are marketed for those purposes.

Magnesium's essentiality is not in question, and the consequences of frank deficiency are well documented. The more useful question is what supplementation does in people with marginal rather than deficient status, and here the evidence is genuinely reasonable for several outcomes.

Meta-analyses have reported modest blood pressure reductions with supplementation, more pronounced in those with elevated readings or low baseline intake. Evidence on sleep quality is mixed but leans positive, particularly in older adults and those with low status. Work on mood and anxiety measures is growing and reasonably encouraging.

Evidence for exercise cramping is weaker than the folk wisdom suggests, with several trials finding no benefit in people with adequate status. As with most nutrients, the size of any effect depends heavily on where you started, and someone with a good dietary intake should not expect much.

Magnesium from supplements is well tolerated by most healthy adults. The dose-limiting effect is gastrointestinal: loose stools, cramping and diarrhoea, most pronounced with the oxide and citrate forms and least with glycinate.

Problems from excess are rare, because healthy kidneys clear it efficiently. Where that clearance is reduced, magnesium can build up, so anyone who has been told their kidneys are not working normally should only supplement under medical guidance.

Magnesium can reduce absorption of several types of medicine if taken at the same time. Separating doses by a couple of hours generally resolves this.