Magnesium is the fourth most abundant mineral in the body and is required as a cofactor in over 300 enzymatic reactions, including those involved in ATP synthesis, protein synthesis, DNA repair, and nerve signal transmission. National Diet and Nutrition Survey data for the UK consistently shows that a significant proportion of adults consume below the reference nutrient intake of 300mg per day for men and 270mg per day for women. The consequences of chronic insufficiency include muscle cramps, poor sleep, anxiety, fatigue, irregular heartbeat, and insulin resistance, all of which are common presenting complaints in clinical practice.
Why Form Matters
Magnesium supplements vary substantially in their bioavailability and in which tissues they preferentially serve. Magnesium oxide, the most common and cheapest form, has absorption of approximately 4 percent and is primarily useful as a laxative. Magnesium citrate has around 30 percent absorption and is well-suited for people with constipation alongside deficiency. Magnesium glycinate, formed by binding magnesium to the amino acid glycine, has high absorption, is well-tolerated, does not cause loose stools, and is the most appropriate form for systemic deficiency correction, sleep, and anxiety applications. Magnesium threonate, which crosses the blood-brain barrier more effectively than other forms, has specific evidence for cognitive support and is the most costly form.
Magnesium and Sleep
Magnesium modulates NMDA receptors and GABA receptors, both of which are central to sleep regulation. A randomised double-blind placebo-controlled trial by Abbasi et al. in elderly adults with insomnia found that magnesium supplementation significantly improved sleep time, sleep efficiency, early morning awakening, and serum melatonin and renin, compared to placebo. The dose used was 500mg per day of elemental magnesium. Glycinate is the preferred form for sleep applications as it combines the magnesium effect with the mild inhibitory effects of glycine on NMDA receptors.
Magnesium and Cardiovascular Health
Magnesium is required for normal cardiac electrical activity and vascular tone. Low serum magnesium is associated with hypertension, atrial fibrillation, and increased all-cause cardiovascular mortality in prospective cohort data. Intravenous magnesium sulphate is a standard hospital treatment for certain arrhythmias. A meta-analysis of prospective studies by Del Gobbo et al. found that each 0.2mmol per litre increase in serum magnesium was associated with a 22 percent lower risk of ischaemic heart disease.
- For sleep and anxiety: magnesium glycinate 200 to 400mg elemental magnesium, taken in the evening
- For constipation with deficiency: magnesium citrate 150 to 300mg, taken with water
- For cognitive support: magnesium threonate 1.5 to 2g daily, taken in divided doses
- Avoid magnesium oxide for systemic deficiency: its absorption is too low to be clinically useful
- Best dietary sources: dark chocolate, pumpkin seeds, spinach, almonds, cashews, and black beans
Sources
- Abbasi, B., et al. (2012). The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences, 17(12), 1161-1169.
- Del Gobbo, L.C., et al. (2013). Circulating and dietary magnesium and risk of cardiovascular disease. American Journal of Clinical Nutrition, 98(1), 160-173.