Magnesium forms overview
The form with the most magnesium per gram is the one your body absorbs worst. That is the whole problem in one line.
Magnesium supplements are a salt or a chelate, and the number on the label is usually the whole compound rather than the magnesium in it. Elemental content ranges from about 60% for oxide down to roughly 16% for citrate, 15% for malate, 14% for glycinate and 8% for L-threonate, so 500mg of one is not 500mg of another. Absorption then runs almost backwards to that. Oxide packs the most magnesium per gram and performs worst: in a 60-day comparison it was indistinguishable from placebo. Citrate is the best-studied of the well-absorbed forms and has the most direct comparative data. Glycinate is the gentle one. Malate and the rest sit in between on thinner evidence. L-threonate is sold on a cognition claim resting on a single 44-person trial run largely by the manufacturer, and it carries the lowest elemental fraction of the lot, so you are paying the most per milligram of actual magnesium for the least-settled claim.
Stack Almanac converts every magnesium form to elemental milligrams before totalling, which is the step that turns four labels in four different units into one number you can compare against a reference intake.
What this is based on
- 1.Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind studyMagnesium Research 2003;16(3):183-91n=46, 60 days; magnesium oxide supplementation resulted in no differences compared to placebo; citrate highest mean serum Mg
- 2.Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humansAmerican Journal of Therapeutics 2001;8(5):345-57comparative pharmacokinetics across magnesium salts in humans
- 3.Efficacy and Safety of MMFS-01, a Synapse Density Enhancer, for Treating Cognitive Impairment in Older Adults: A Randomized, Double-Blind, Placebo-Controlled TrialJournal of Alzheimer's Disease 2016;49(4):971-90the single pivotal magnesium L-threonate cognition trial: n=44 (23 active, 21 placebo), 12 weeks, ages 50-70; all authors bar two affiliated with Neurocentria, the manufacturer; sleep and anxiety effects could not be determined because of placebo effects
- 4.MagnesiumExamine.comoxide and carbonate have extremely poor absorption and increased risk of gastrointestinal side effects; citrate consistently shows good bioavailability; US IOM UL of 350 mg/day applies to supplemental magnesium only
See also the full reference for magnesium.
Stack Almanac does this comparison against your own stack