Magnesium

Magnesium is a cofactor in hundreds of enzymatic reactions, so the supplement literature spans an unusually wide range of physiological systems. The outcome dimensions covered most heavily include sleep quality (particularly in older adults and people with subclinical deficiency), blood pressure and other cardiovascular markers, glycemic control in type 2 diabetes and prediabetes, migraine prevention, muscle cramps and restless legs, and anxiety. Bone mineralization sits at the foundational end alongside calcium. Exercise performance and recovery are smaller research streams.

Most randomized trials test a single form rather than comparing forms head-to-head, and by form the trial record is very uneven. Among forms sold as supplements, oxide has the largest trial record, across blood sugar, constipation, blood pressure, migraine, sleep and leg cramps. Citrate has more trial records than oxide on PubMed, but about two thirds of them test it as a bowel cleanser before medical procedures; the rest cover migraine, leg cramps, sleep and blood pressure. In blood-pressure trials, aspartate and chloride are used about as often as oxide. Glycinate has a small human trial record, including one placebo-controlled sleep trial and one on leg cramps in pregnancy. L-threonate has a handful of small trials, mostly on cognition and sleep, and those were funded by companies that develop or sell it; the claim that it raises magnesium in the brain comes from animal studies, and the human trials did not measure brain magnesium. Malate and taurate have almost no human trial evidence.

On absorption, NIH notes that small studies found oxide less completely absorbed than citrate, chloride, lactate or aspartate. Those studies measured magnesium levels in healthy volunteers, not health effects, and which form is absorbed best has not been established. As of October 2026, PubMed lists no trial comparing glycinate with citrate for any health condition.

Demographically, the literature is weighted toward older adults (especially in sleep and bone outcomes) and toward clinical populations such as people with type 2 diabetes or migraine. Healthy young populations and women across reproductive years are less represented. Sleep trials have used different schedules: some gave magnesium in the evening before bed, one after breakfast, and others split it across the day. None compared one time of day with another, so whether timing matters is untested. Trials often do not measure baseline magnesium status (a non-trivial assay), so distinguishing a true treatment effect from correction of subclinical deficiency is often impossible from a single study.

The most common adverse effect of supplemental magnesium is gastrointestinal: loose stools and diarrhea, more likely at higher doses. NIH lists the carbonate, chloride, gluconate and oxide forms as the ones most commonly reported to cause diarrhea, and the citrate, hydroxide, oxide and sulfate forms are also used as laxatives. The IOM tolerable upper limit for supplemental magnesium in adults is 350 mg/day; this limit refers to supplement-derived intake because dietary magnesium from food does not produce the same effects. Magnesium can reduce the absorption of two families of antibiotics (quinolones, and those whose names end in -cycline), bisphosphonates (osteoporosis medicines) and synthetic thyroid hormone (T4). NIH says to take bisphosphonates at least 2 hours apart from magnesium, and these antibiotics at least 2 hours before or 4 to 6 hours after it; the labelling of that thyroid medicine calls for a 4-hour gap from products that interfere with its absorption. Potassium-sparing diuretics (a type of water pill) cause the body to hold on to magnesium. People with chronic kidney disease should not supplement without medical supervision, since impaired renal excretion can lead to hypermagnesemia (high blood magnesium). Sources: IOM Dietary Reference Intakes report, NIH ODS magnesium fact sheet, and the FDA-approved labelling of synthetic T4 thyroid hormone.

This summary is informational and not medical advice. Consult a clinician before starting or changing any supplement, especially if you take prescription medications.