Magnesium
Essential mineral involved in 300+ body processes
What is Magnesium?
Magnesium is the fourth most abundant mineral in the human body. It's a cofactor in over 300 enzyme reactions, including energy production (ATP synthesis), DNA and protein synthesis, muscle contraction and relaxation, nerve signal transmission, and blood glucose regulation. Despite its importance, NHANES data suggests 48% of Americans and similar proportions of UK adults consume below the RNI.
How it works
Magnesium modulates N-methyl-D-aspartate (NMDA) receptors, which are excitatory glutamate receptors. By acting as an NMDA antagonist, magnesium reduces neural excitability — this explains its anxiolytic and sleep-promoting effects. It also activates GABA receptors (inhibitory) and regulates calcium channel activity in muscle cells, which governs contraction and relaxation.
What the evidence shows
Strongest evidence for: sleep quality (2012 RCT in older adults with insomnia showed significant improvements), PMS symptoms (multiple RCTs showing reduction in anxiety, mood, and cramp severity), type 2 diabetes prevention (high intake inversely associated with T2D risk in meta-analyses), blood pressure reduction (particularly in hypertensive individuals), and migraine prevention (2:1 benefit vs placebo in several trials).
When to expect results
Sleep quality often improves within the first week — particularly falling asleep faster and more restful sleep.
Reduced muscle cramps, improved morning energy, lower baseline anxiety becoming noticeable.
PMS symptom reduction, sustained sleep quality, improved stress resilience.
Consistent effects across all areas. Long-term benefits for blood pressure and glucose metabolism accumulate.
Dosing
Target 300–400mg elemental magnesium daily. RNI is 270mg for women, 300mg for men. Most benefit is seen above 300mg. For sleep: take 300–400mg glycinate 30–60 minutes before bed. Note that 'magnesium oxide 500mg' provides only ~20mg elemental magnesium due to 4% absorption.
Forms to choose
Form matters enormously. Glycinate (bisglycinate): highest bioavailability, best for sleep and anxiety, gentlest on stomach. Citrate: good bioavailability, mild laxative at high doses. Malate: good for energy and fibromyalgia. L-Threonate: premium, crosses blood-brain barrier better for cognitive applications. Oxide: 4% absorption — avoid for supplementation purposes.
Who benefits most
Athletes (lost in sweat), people with high stress (magnesium is depleted by cortisol), women with PMS, anyone with poor sleep, older adults (absorption decreases with age), people with type 2 diabetes or insulin resistance, heavy coffee drinkers (caffeine increases urinary magnesium excretion).
Who should avoid / caution
People with kidney disease should use caution — kidneys regulate magnesium excretion. Discuss with GP before supplementing if you have renal impairment.
Interactions & stacking
Magnesium is required to convert vitamin D to its active form. If deficient in both, supplementing D without Mg is inefficient.
Both promote GABA activity. Combining produces synergistic calming and sleep-onset effects.
High-dose zinc (above 40mg) competes with magnesium absorption. Separate by 2+ hours if supplementing both at high doses.
Balance matters: the ideal Ca:Mg ratio is approximately 2:1. Very high calcium without adequate magnesium may impair magnesium utilisation.
Safety & side effects
Generally very safe. Too much at once can cause loose stools (especially citrate and oxide). Glycinate is the most GI-friendly form. Very high supplemental doses (above 5,000mg elemental) may cause hypermagnesaemia, but this is extremely rare from oral supplementation in people with normal kidney function.
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This information is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, particularly if you are pregnant, breastfeeding, have a medical condition, or are taking prescription medication.