The Key Question: Which Form?
Not all magnesium forms are equal — this is the most common mistake when buying. Many cheap products contain magnesium oxide, with a bioavailability of around 4–5%, which makes it largely pointless.
| Form | Bioavailability | Best suited for |
|---|---|---|
| Magnesium glycinate | Very high (~80%) | Sleep, nerves, general — good tolerability |
| Magnesium citrate | High (~65%) | General; mildly laxative at high doses |
| Magnesium L-threonate | High (brain-specific) | Cognition; more expensive |
| Magnesium malate | High (~60%) | Energy, muscle soreness |
| Magnesium oxide | Very low (~4–5%) | Rarely worth buying as a supplement |
Why Is Magnesium Deficiency So Common?
National dietary surveys in Germany (NVS II) indicate that approximately 26–29% of German adults consume less magnesium than recommended by the DGE. Those particularly affected include:
- Regular alcohol consumption (increases renal excretion)
- Intense sweating through sport (loss in sweat)
- Use of proton pump inhibitors (e.g., omeprazole) or diuretics
- Type 2 diabetes (increased renal loss)
- Older adults (reduced absorption, lower dietary intake)
Surveys in other European countries report similar patterns.
What Is Well Established?
Blood pressure
A meta-analysis of 34 RCTs (Zhang et al. 2016, n=2,028) showed: magnesium supplementation lowered systolic blood pressure by an average of ~3–4 mmHg and diastolic by ~2–3 mmHg. The effect was stronger in people with low baseline levels and higher blood pressure — clinically relevant as an adjunct in hypertension management, not a replacement for medication.
Sleep quality
An RCT (Abbasi 2012, n=46 older adults) showed: 500 mg magnesium/day over 8 weeks significantly improved sleep quality, sleep duration, and insomnia scores vs. placebo. The subgroup of older individuals with low magnesium levels benefited most.
Insulin sensitivity in deficiency
Guerrero-Romero et al. (2004) demonstrated in an RCT: 2.5 g MgCl₂/day (equivalent to ~300 mg elemental magnesium) over 3 months significantly reduced insulin resistance in individuals with magnesium deficiency. Effect on insulin sensitivity in people with normal magnesium levels is less well established.
Prediabetes — new 2026 meta-level signal: A systematic review and meta-analysis (PMID 41641401) consolidates the human evidence at the point where magnesium is most clinically plausible: in people with dysregulated glucose metabolism but not yet overt type 2 diabetes. The paper does not make magnesium a miracle treatment, but it does support taking the ingredient more seriously in prediabetes — especially where low intake or functional deficiency is likely.
Energy and enzymatic functions
Magnesium is a cofactor for over 300 enzymatic processes, including ATP synthesis, DNA repair, and protein synthesis. EFSA has approved corresponding claims for normal energy metabolism and reduction of fatigue based on this fundamental biochemical role.
Migraine prophylaxis
German neurological guidelines recommend magnesium (400–600 mg/day) as prophylaxis for migraine in those with documented deficiency — one of the few non-pharmacological options with consistent evidence from multiple RCTs.
What Is Less Certain?
Magnesium L-threonate as a cognition booster: The animal study by Slutsky et al. (2010) showed impressive memory effects in rodents, but human studies are still small and short-term. Direct cognitive improvement in healthy people without deficiency: not established.
Direct longevity effects: No RCT evidence that magnesium supplementation extends lifespan in adequately nourished individuals.
Depression treatment: Some studies show associations with mood, but evidence quality for therapeutic effects is limited.
Dosage
EU Reference Intake: 375 mg/day (on supplement labels). National guidelines vary slightly.
With supplementation: 200–400 mg elemental magnesium/day. Higher doses can have a laxative effect (osmotic effect in the gut — some people use magnesium citrate deliberately for constipation). Highly bioavailable forms such as magnesium glycinate have fewer gastrointestinal side effects.
When to take: Evening (before bed) is frequently recommended — particularly for sleep issues and magnesium glycinate. Food slows absorption slightly but generally improves tolerability.
Research Limitations
- Many studies have short durations (under 3 months) and small sample sizes
- Heterogeneous study designs make meta-analyses difficult (different forms, doses, populations)
- Deficiency is difficult to define: serum magnesium reflects only ~0.3% of total body magnesium and is an insensitive marker
- Positive effects on blood pressure and insulin sensitivity apply primarily to deficient populations
EFSA Status
Magnesium is one of the most broadly recognised ingredients in the EFSA health claims register. Approved claims include:
- Normal energy metabolism
- Normal nervous system and psychological function
- Normal muscle contraction and function
- Reduction of tiredness and fatigue
- Normal protein synthesis
- Normal bone and teeth
Summary
Magnesium is a genuine foundational nutrient with broad EFSA recognition and consistent evidence for several clinical endpoints. In deficiency — which is widespread — supplementation is reasonable. Choosing a bioavailable form is essential; magnesium oxide is typically a waste of money.