Magnesium L-threonate: what dose, when, and what the two trials really show
· by VEXTA Team
What dose, and how much magnesium really?
Both published trials use 2 g per day of magnesium L-threonate. That is the figure to remember — but it misleads if read as a magnesium dose.
Magnesium L-threonate is a salt: of 2 g of compound, elemental magnesium accounts for roughly 144 mg. The remainder is L-threonic acid, the carrier molecule that gives this salt its particular transport properties. This is why comparing it directly with a bisglycinate delivering 300 mg of elemental magnesium makes no sense: the two target different compartments.
For reference, the upper safety limit retained for magnesium from food supplements is 250 mg per day, with gastrointestinal effects described from around 360 mg. The 144 mg supplied by 2 g of magnesium L-threonate sits clearly below that.
What Liu 2016 shows
Liu 2016 (Journal of Alzheimer's Disease, DOI 10.3233/JAD-150538): a randomised, double-blind, placebo-controlled, parallel-design trial in adults aged 50 to 70 with cognitive impairment — 23 on treatment, 21 on placebo, over 12 weeks.
Overall cognitive ability, measured by a composite score across four domains, improved significantly against placebo (p = 0.003; Cohen's d = 0.91), and cognitive fluctuation was reduced. The study population had more severe executive function deficits than age-matched normative controls, and treatment brought that function close to normal.
The point commercial summaries invariably omit: effects on sleep and anxiety could not be determined in this trial, because of an overwhelming placebo effect on both measures.
What Lopresti 2025 shows
Lopresti 2025 (Frontiers in Nutrition, DOI 10.3389/fnut.2025.1729164): a randomised, double-blind, placebo-controlled trial in 100 adults aged 18 to 45 reporting dissatisfaction with their sleep, at 2 g per day for six weeks.
- Overall cognitive performance (NIH Total Cognition Composite) improved versus placebo, p = 0.043, with the largest effects on working and episodic memory
- Estimated brain cognitive age reduced by 7.5 years
- Reaction time improved, p = 0.031
- Resting heart rate lowered (p = 0.030) and heart rate variability increased (p = 0.036)
- Raven's Progressive Matrices: no difference (p = 0.953)
On sleep the result is partial and worth stating precisely: sleep-related impairment improved (p = 0.043), but there was no difference in sleep disturbances themselves (p = 0.316) or restorative sleep (p = 0.439). A signal emerged on sleep disturbances only in the subgroup of participants most affected (p = 0.031). Data from the sleep-tracking ring showed no difference in sleep outcomes.
When to take it
Both trials split intake across the day, with a portion in the evening. That evening dose is what drives the common association with sleep, but no trial compares a single evening dose with a split schedule. In practice, splitting into two — one of them in the evening — most closely reproduces what was studied.
The consistent evaluation window is 6 to 12 weeks, matching the two published trials.