Magnesium

Magnesium is a cofactor for over 300 enzymes, including every enzyme in the vitamin D pathway (see D + Mg + K2), the ATP synthase complex, and enzymes that regulate neuronal excitability and cardiac rhythm. Roughly half of US adults consume less than the estimated average requirement.

Daily requirements

• Adult men (19–30): 400 mg/day.
• Adult men (31+): 420 mg/day.
• Adult women (19–30): 310 mg/day.
• Adult women (31+): 320 mg/day.
• Pregnancy: 350–400 mg/day.
• Tolerable Upper Intake Level (from supplements only): 350 mg elemental Mg/day.

Deficiency

Serum magnesium is not a sensitive test — only 1% of body magnesium is in serum. Chronic subclinical deficiency is common and hard to detect. Symptoms of overt deficiency include muscle cramps, twitching, fatigue, irritability, palpitations, migraines, and difficulty sleeping. Severe hypomagnesaemia causes tetany and cardiac arrhythmia.

Common causes of magnesium deficiency

• Diet low in leafy greens, legumes, nuts, and whole grains
• Chronic alcohol use — impairs absorption, increases renal loss
• Proton pump inhibitors (chronic use)
• Diuretics (loop, thiazide)
• Type 2 diabetes (renal wasting)
• Malabsorption disorders (celiac, Crohn's, short bowel)

Forms of magnesium supplements compared

Evidence-based clinical uses

• Migraine prophylaxis — 400–600 mg/day (glycinate or citrate); modest reduction in frequency.
• Sleep quality — small trials show benefit for insomnia in older adults.
• Constipation — magnesium citrate or oxide at 200–400 mg.
• Preeclampsia — IV magnesium sulphate is standard obstetric care for severe preeclampsia and eclampsia prevention.
• Type 2 diabetes — small improvements in insulin sensitivity in deficient patients.

Food sources

• Pumpkin seeds (1 oz): 156 mg
• Almonds (1 oz): 80 mg
• Spinach (½ cup cooked): 78 mg
• Cashews (1 oz): 74 mg
• Black beans (½ cup cooked): 60 mg
• Dark chocolate (1 oz, 70%): 65 mg
• Whole-grain bread, brown rice, quinoa — 30–70 mg/serving