The Practical Takeaway
Check your diet first
Dark leafy greens (spinach, kale), pumpkin seeds, almonds, cashews, black beans, and dark chocolate are all high in magnesium. If these show up in your diet most days, you're almost certainly replete — supplementation is unlikely to help your sleep.
If diet is poor AND sleep is poor: how to supplement correctly
Take 250–350mg of elemental magnesium as bisglycinate, 1–2 hours before bed. Read the nutrition facts panel for elemental content — the front label shows compound weight, which is 6–7x higher. Give it 6–8 weeks minimum — rebuilding stores inside cells takes time.
Avoid magnesium oxide for sleep
Only about 4% of oxide gets absorbed — it works mainly as a laxative. The studies that used oxide and showed sleep results were in elderly patients; your absorption profile will differ. Use bisglycinate.
Skip the L-threonate premium
The "crosses into the brain" claim comes from rat studies. A 2026 review found zero human studies confirming superior brain delivery versus bisglycinate. The premium isn't justified by the evidence.
Athletes: diet first, then check before supplementing
Training does raise magnesium requirements slightly (about 10–20% more via sweat and urine). But athletes eating whole foods typically cover this gap without supplements. Confirmed well-nourished athletes gain nothing from supplementation — some evidence suggests excess can reduce peak muscle contraction force.
