Bone and soft tissues contain most of it
NIH ODS describes an adult body as containing approximately 25 g magnesium, with about 50–60% in bone and most of the rest in soft tissues. Less than 1% is in blood serum. These are approximate physiological descriptions, not a personal inventory that can be calculated precisely from body weight. [1]
A blood result is not a direct total-body measurement
Serum magnesium is commonly measured, but it does not closely reflect the entire amount in tissues or bone. That limitation does not make the test useless or justify diagnosing deficiency from symptoms alone. Clinical assessment, medicines and relevant testing all influence interpretation; ODS notes that no single assessment method is satisfactory in every setting. [1]
A compartment example
Using the approximate 25 g figure only as an illustration, 50–60% corresponds to about 12.5–15 g in bone. Less than 1% would be less than 0.25 g in serum. This is not a supplement calculation: it would be wrong to try to replace estimated body stores with an equivalent oral dose. [1]
| Illustrative compartment | Arithmetic using25g | Interpretation |
|---|---|---|
| Bone | 25 ×0.50 to 25 ×0.60 =12.5–15 g | Approximate distribution |
| Serum | Less than 25 ×0.01 =0.25 g | Small regulated compartment |
| Supplement need | Not derivable from these totals | Requires a nutritional or clinical assessment |
Sources for this article
- Magnesium - Health Professional Fact Sheet
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product.