Many adults take in less magnesium than national targets, and closing that gap is what most evidence addresses. Best supported: a small blood-pressure fall, better blood-sugar handling, fewer migraine attacks. Harms are mostly loose stools, largely governed by the chemical form, plus reduced absorption of some medicines taken together; serious buildup is confined to impaired kidneys. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum magnesium | 0.85–0.95 mmol/L | Detects overt deficiency and, at the top end, over-repletion |
| Red-blood-cell magnesium | 5.0–6.5 mg/dL | Reflects intracellular stores far better than serum, so it detects long-running tissue deficit |
| eGFR and creatinine | Above 60 mL/min/1.73 m² | Establishes that excretion capacity is intact before and during supplementation |
| Serum potassium and calcium | Potassium 4.0–4.5 mmol/L; calcium 2.2–2.4 mmol/L | Magnesium deficiency causes potassium and calcium loss that will not correct until magnesium is replaced |
| HbA1c and fasting insulin | HbA1c below 5.4%; fasting insulin below 6 µIU/mL | Tracks the glucose and insulin-sensitivity benefit, one of magnesium's better-supported effects |
| 25-hydroxyvitamin D | 40–60 ng/mL | Magnesium activates vitamin D, so the two must be interpreted together |
| hs-CRP | Below 1.0 mg/L | General inflammation marker; the evidence that magnesium moves it is conflicted, so treat it as exploratory |
| Home blood pressure | Below 120/80 mmHg | The most responsive and cheapest objective measure of magnesium's cardiovascular effect |
Cadence: Baseline before starting; blood pressure at 2 weeks and 3 months; magnesium and kidney function at 3 months, then annually if kidney function is normal and the dose is stable; every 6 months with reduced filtration or above 350 mg/day supplemental.