Magnesium

•RCT evidence— Multiple BP meta-analyses; sleep + migraine smaller trials

Why it matters

• Cofactor for 300+ enzymes including ATP synthesis, DNA repair, glucose metabolism.
• Population-level deficiency: ~50% of US adults below RDA.
• Serum magnesium is a poor reflection of total-body status; RBC magnesium or ionised magnesium are better but not routine.

Forms (matters for absorption and effect)

Form	Bioavailability	Best for
Glycinate / bisglycinate	High	Sleep, anxiety, general
Citrate	High	Constipation, general
L-threonate	High	Cognitive (crosses BBB)
Malate	High	Fatigue, fibromyalgia
Chloride	High	Topical / spray
Oxide	Very low	Avoid (used in cheap supplements)
Sulphate	Low oral	IV use; Epsom-salt baths

Evidence-based uses

• Blood pressure: meta-analysis shows ~2/1.8 mmHg reduction with ~300 mg/day; larger in baseline-deficient.
• Sleep onset: small benefit, particularly glycinate.
• Migraine prevention: ~400–600 mg/day reduces frequency in meta-analyses.
• Type-2 diabetes: improves insulin sensitivity in deficient adults.
• Constipation: citrate effective laxative.

Cautions

• Renal impairment: risk of hypermagnesaemia.
• PPI users: long-term PPI use can cause magnesium deficiency.
• High doses can interfere with absorption of some antibiotics, levothyroxine.

Related entries

Blood pressure, Sleep optimization, Type 2 diabetes.