Mineral Forms Compared: Elemental Percentage and Absorption Reference
THE SHORT ANSWER
Minerals are always bound to something else, and that partner molecule changes how much you absorb, what it does to your gut, and how much actual mineral a milligram figure represents. This is a reference table of the common forms — magnesium, iron, zinc, selenium, chromium and calcium — with elemental percentage, absorption, and tolerability for each. The elemental column is the one that catches people: magnesium glycinate is roughly 14% magnesium by weight, magnesium oxide roughly 60%, which is why the cheaper form always looks stronger on a label.*
01The concept that makes the tables useful
Two numbers appear on mineral labels and only one matters.
Compound weight is the weight of the whole molecule — mineral plus whatever it is bound to. Elemental weight is the mineral itself.
"Magnesium glycinate 1,000 mg" and "magnesium 140 mg" can describe the same capsule. In the United States the Supplement Facts panel is required to state the elemental amount, so the back of the bottle is reliable. Front labels frequently use compound weights because they produce larger numbers.
The percentages below let you check whether a front-label figure is compound or elemental.
02Magnesium
| Form | Elemental % | Absorption | Laxative effect | Notes |
|---|---|---|---|---|
| Oxide | ~60% | Poor | Strong | Cheap; high elemental % flatters labels |
| Citrate | ~16% | Moderate | Moderate–strong | Also sold as a laxative |
| Glycinate / bisglycinate | ~14% | Good | Minimal | Glycine has its own calming activity |
| Malate | ~15% | Good | Low | Malic acid feeds the energy pathway |
| Taurate | ~9% | Good | Low | Taurine has cardiovascular roles |
| L-threonate | ~8% | Good | Low | Low elemental content; studied for CSF levels |
| Chloride | ~12% | Moderate | Moderate |
Upper limit: 350 mg elemental daily from supplements. Food magnesium has no limit. The limit marks where loose stools become likely, not harm — see what the 350 mg limit means and which magnesium to take.
03Iron
| Form | Elemental % | Absorption | Tolerability | Notes |
|---|---|---|---|---|
| Ferrous sulfate | ~20% | Good | Poor | Clinical default; most digestive complaints |
| Ferrous gluconate | ~12% | Good | Moderate | Gentler partly because less iron per dose |
| Ferrous fumarate | ~33% | Good | Moderate | Higher elemental content |
| Ferrous bisglycinate | ~20% | Good | Good | Chelated; far better tolerated |
| Carbonyl iron | ~98% | Slow | Good | Slow absorption reduces overdose risk |
Critical: the body has no active route to excrete iron. Test ferritin before supplementing. Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6 — keep out of reach. See the iron guide.
04Zinc
| Form | Elemental % | Absorption | Notes |
|---|---|---|---|
| Oxide | ~80% | Poor | Common in low-cost multivitamins |
| Gluconate | ~13% | Good | Lozenge standard |
| Citrate | ~31% | Good | Better taste for chewables |
| Picolinate | ~20% | Good | Picolinic acid is the body's own transport chelator |
| Bisglycinate | ~20% | Good | Chelated to glycine |
| Sulfate | ~23% | Adequate | Most likely to cause nausea |
Upper limit: 40 mg daily from all sources. Sustained high zinc blocks copper absorption via metallothionein — see zinc picolinate.
05Selenium
| Form | Type | Absorption | Notes |
|---|---|---|---|
| Selenomethionine | Organic | Good | Stored in body proteins |
| Selenium yeast | Organic | Good | Composition varies by producer |
| Selenium glycinate | Chelate | Good | Gentle |
| Sodium selenite / selenate | Inorganic | Lower | Cheaper; not stored the same way |
The narrowest window of any mineral here: 55 mcg recommended, 400 mcg upper limit. Dose matters more than form. See selenium.
06Calcium and chromium
| Form | Elemental % | Notes |
|---|---|---|
| Calcium carbonate | ~40% | Needs stomach acid; take with food |
| Calcium citrate | ~21% | Absorbed without acid; suits acid-reducer users |
| Chromium picolinate | ~12% | Most studied chromium form |
| Chromium polynicotinate | ~10% |
07The general pattern
Reading down the tables, three rules emerge.
High elemental percentage usually means poor absorption. Oxides are the clearest case — magnesium oxide at 60% and zinc oxide at 80% are the cheapest and least absorbed. The number that flatters the label is the number that signals the weaker form.
Chelates trade elemental content for absorption and tolerability. Binding a mineral to an amino acid adds weight, so the percentage falls — but more of what is there reaches you, and less unabsorbed mineral is left in the gut causing trouble.
The gap between forms is not equal across minerals. It is very wide for magnesium (glycinate versus oxide) and considerably narrower for zinc, which absorbs reasonably in several forms. Worth knowing before paying a premium.
08What to check on any mineral label
Elemental amount on the Supplement Facts panel, not the front.
Ingredient order — descending by weight, so a cheap form listed first is the dominant one regardless of what else is named.
Words like "blend" or "buffered", which frequently signal oxide has been added to lift the elemental figure.
Proprietary blends, which hide the split between forms. No manufacturer conceals a flattering ratio.
A certificate of analysis for your lot. Minerals are mined, which makes heavy metal testing relevant rather than a formality. Ours are on the certificate page.
09Frequently asked questions
What does elemental mean on a mineral supplement?
The actual mineral, as opposed to the weight of the whole compound. Magnesium glycinate is roughly 14% magnesium by weight.
Why does magnesium oxide have more magnesium?
By weight it does — around 60% versus 14% for glycinate. But it is poorly absorbed, so more of it passes through rather than reaching you.
Are chelated minerals always better?
Not always. The advantage is large for magnesium and meaningful for iron, but narrower for zinc, which absorbs reasonably in several forms.
How do I know if a product uses a cheap form?
Ingredients are listed in descending order by weight. Terms like blend or buffered often indicate oxide has been added.
Which minerals have upper limits?
Supplemental magnesium at 350 mg, zinc at 40 mg, and selenium at 400 mcg are the ones worth carrying. Iron has no simple limit but cannot be excreted.
Do these percentages vary by manufacturer?
Slightly, since chelation completeness varies. The figures here are typical rather than exact.
Which minerals compete with each other?
Iron, zinc, calcium and magnesium all compete at higher doses. See the interactions reference.
Why do some forms cause loose stools?
Poorly absorbed mineral draws water into the bowel by osmosis. That is why magnesium oxide and citrate are sold as laxatives.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Elemental percentages are typical values and vary slightly by manufacturer.
