Two numbers can describe different things
The weight of magnesium glycinate or L-threonate as a chemical compound is not identical to elemental magnesium. Compare like-for-like values from the Supplement Facts panel. Do not treat the largest number on the front of a bottle as evidence of a stronger or better product.
The form does not answer the benefit question
The research question for sleep or cognition is distinct from the question of how much magnesium a product provides. Ingredient chemistry, population, study methods and outcomes all matter. Terms like “brain magnesium” are marketing shorthand, not a guaranteed change in brain health.
Be cautious with stacking
More than one supplement can contribute magnesium, and some multivitamins contain it already. Total exposure and relevant medical conditions affect safety. People with kidney conditions or interacting medicines need individual clinical guidance.
Build a fair comparison table
Write down formulation, elemental magnesium per serving, number of servings, cost, other ingredients, tolerability and the study claims the company references. Skip products whose labels are too opaque to compare.