Magnesium

Magnesium is a cofactor in over 300 enzyme systems — it's involved in protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. This deficiency-correction role is decades-old, well-established science. The newer marketing angle — magnesium glycinate specifically for sleep and relaxation — is a much more recent claim, and it's worth treating those two roles as separate claims with very different levels of evidence behind them.

Deficiency correction: per the NIH Office of Dietary Supplements, magnesium's roles in muscle contraction, nerve transmission, bone structure, and glucose/blood pressure regulation are well-established and supported by decades of research. This is the strong, settled part of magnesium's evidence base.

Read the NIH fact sheet →

Glycinate and sleep — genuinely preliminary: a 2025 double-blind, placebo-controlled trial in adults reporting poor sleep (n=155) tested 250mg of elemental magnesium as magnesium bisglycinate nightly for 4 weeks and found a small but statistically significant improvement in insomnia severity scores. It's a real, well-designed trial — but it's also short (4 weeks), relies on subjective self-reported outcomes, and stands largely alone rather than as part of a large, consistent body of research specific to the glycinate form.

Being honest about the evidence gap here: magnesium's deficiency-correction role has decades of research behind it; magnesium glycinate's sleep-specific benefit has a much thinner, newer, and smaller evidence base. If you're not magnesium-deficient, the sleep effect (if any) is likely to be modest — this is a supplement where the marketing has outpaced the research more than most.

Per the NIH Office of Dietary Supplements, the RDA for adults is roughly 400–420mg/day for men and 310–320mg/day for women. The sleep trial above used 250mg/day of elemental magnesium as bisglycinate, taken in the evening — a reasonable reference point if trying that specific form, though it isn't an official dosing guideline the way the RDA is.

The most common side effect is GI upset — diarrhea, nausea, cramping — driven by unabsorbed magnesium drawing water into the gut; this is more common with oxide and citrate forms and less common with glycinate/chelated forms, per the NIH fact sheet. Magnesium can reduce the absorption of certain antibiotics, including tetracyclines (e.g., doxycycline) and quinolones (e.g., ciprofloxacin, levofloxacin) — the NIH recommends spacing doses apart if taking both. Anyone with kidney disease should talk to a doctor before supplementing, since impaired kidneys have a reduced ability to excrete excess magnesium.