Magnesium Glycinate vs Threonate vs Citrate

The Elemental Content Problem

Before comparing forms, the label arithmetic has to be understood, because it causes more confusion than any pharmacological difference.

Magnesium is always supplied as a compound, and the elemental magnesium is a fraction of the total weight. Magnesium oxide is roughly 60 percent elemental magnesium; magnesium citrate around 11 to 16 percent depending on hydration state; magnesium glycinate around 14 percent; magnesium L-threonate around 8 percent.

So "500 mg magnesium glycinate" typically means about 70 mg of elemental magnesium, and reaching 300 mg of elemental magnesium from that product requires roughly four capsules. Good labels state elemental content explicitly, often as "magnesium (as magnesium bisglycinate) 100 mg". Labels that state only the compound weight are, at best, unhelpful.

This is why comparing forms by capsule count or by compound weight is meaningless, and why magnesium oxide products can appear to deliver high doses while absorbing poorly.

Form by Form

Magnesium glycinate (bisglycinate)

Magnesium chelated to two glycine molecules. Well absorbed, and notably gentle on the gut, which is the practical reason it dominates recommendations for repletion. The glycine component is not incidental: glycine at 3 grams has its own evidence for improved sleep quality and next-day alertness, though the amount delivered alongside a typical magnesium dose is well below that.

Best for: general repletion, sleep, stress, anyone who has had loose stools from other forms.

Magnesium L-threonate

Magnesium bound to L-threonic acid, a metabolite of vitamin C. Developed and studied specifically for raising magnesium concentrations in the central nervous system, with animal work reporting increased cerebrospinal fluid magnesium and effects on synaptic density. Small human trials report cognitive effects, and the evidence base is thinner than the marketing.

Best for: cognitive objectives specifically. Drawback: low elemental content and high cost, so it is a poor choice for general repletion.

Magnesium citrate

Magnesium bound to citric acid. Among the best-absorbed forms in comparative studies, and osmotically active in the gut, which produces a mild laxative effect. That effect is the reason it is used clinically for constipation and bowel preparation at higher doses.

Best for: repletion where a mild laxative effect is acceptable or wanted, and cost-effective absorption. Drawback: the laxative effect at higher doses.

Others worth knowing

Malate: moderate to good absorption, with malate feeding the citric acid cycle, though evidence for that pairing mattering is thin. Taurate: pairs magnesium with taurine, which has independent cardiovascular activity. Oxide: high elemental content, poor absorption, appropriate mainly for bowel regularity and dominant in cheap products. Chloride and sulfate topically: transdermal absorption is not well supported by evidence.

Side-by-Side

Elemental percentages vary with hydration state and specific salt, so read them as approximate.

How to Choose

The decision is almost entirely determined by objective, which is unusual among supplement comparisons and is why this one has a clean answer.

• Sleep onset or stress: glycinate, 200 to 400 mg elemental, thirty to ninety minutes before bed.
• General repletion, gut-sensitive: glycinate, split across the day.
• General repletion, cost-sensitive, no gut issue: citrate.
• Repletion plus constipation: citrate, and the laxative effect becomes a feature.
• Cognitive objective specifically: threonate, accepting the cost and thinner evidence, and ideally alongside a cheaper form for total repletion rather than relying on it for both.
• Bowel regularity only: oxide, which is cheap and does that one job.
• Migraine prophylaxis: any well-absorbed form at 400 to 600 mg elemental per day, which is the range in headache guidance.

A common and reasonable pattern is two forms for two objectives: a well-absorbed form for total intake and a small evening dose of glycinate for sleep. What is not reasonable is buying threonate for general repletion, since the cost per unit of elemental magnesium is several times higher for no additional benefit outside the cognitive objective.

Dose, Timing and Cautions

Total intake targets are roughly 400 to 420 mg of elemental magnesium daily for adult men and 310 to 320 mg for adult women, from all sources including food. Supplemental amounts of 200 to 400 mg elemental are typical, and the tolerable upper intake for supplemental magnesium is usually stated as 350 mg per day, above which loose stools become likely. That limit applies to supplements rather than to food, which has no established upper limit.

Fractional absorption falls as a single dose rises, so splitting improves total uptake. For sleep objectives, evening dosing is both conventional and mechanistically supported.

Two cautions matter. Anyone with reduced kidney function should not supplement magnesium without clinical oversight, since impaired clearance allows accumulation and hypermagnesaemia is a genuine clinical problem. And magnesium reduces absorption of tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine, which is resolved by separating doses by at least four hours rather than by avoiding it.

On testing: serum magnesium is widely available and weakly informative, since under one percent of body magnesium is in serum and the concentration is defended by bone exchange and renal reabsorption. Red blood cell magnesium reflects status somewhat better. In practice, dietary intake assessment plus response to a supplementation trial is often more informative than a blood test, which is an unusual situation worth stating plainly.