Magnesium Supplements: Glycinate vs Citrate vs Oxide — A UK Evidence Guide

Magnesium is the fourth most abundant mineral in the human body and a cofactor in more than 300 enzymatic reactions, including ATP energy production, DNA synthesis, protein synthesis, muscle contraction, and nerve signal transmission. It is also required for the activation of vitamin D — a relationship with direct relevance to UK adults given widespread deficiency in both nutrients. Despite its importance, magnesium inadequacy is widespread. Surveys estimate that roughly 48% of Americans and around 20% of Europeans consume less than their country's recommended daily intake. In the UK, the Reference Nutrient Intake (RNI) is 300 mg/day for adult men and 270 mg/day for adult women. Dietary sources include green leafy vegetables, nuts, seeds, whole grains, and legumes — foods that are underrepresented in many modern diets. Processing and cooking can leach magnesium from food, and certain medications increase urinary losses. Long-term proton pump inhibitor (PPI) use — prescribed to millions in the UK for acid reflux — is a well-documented cause of hypomagnesaemia. Older adults are at heightened risk owing to reduced intestinal absorption and increased renal excretion. Blood tests are an unreliable guide: only around 1% of total body magnesium is in serum, so serum levels can appear normal even when intracellular and bone stores are depleted. Subclinical deficiency does not produce dramatic symptoms, which is why it often goes unrecognised. Fatigue, muscle tension, and poor sleep are common complaints that may, in some individuals, reflect inadequate magnesium status rather than a primary disorder.