The form decoder.
"Magnesium" on the front of the bottle can mean very different things on the back. Pick an ingredient to compare its common forms on absorption, tolerability, and how much actual mineral you get.
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Method & sources
Each comparison reflects general bioavailability and tolerability findings from the research literature and the NIH Office of Dietary Supplements - for example, soluble magnesium salts (citrate, glycinate) are absorbed more completely than oxide; vitamin D3 raises blood levels more effectively than D2; and curcumin is poorly absorbed unless paired with piperine or a phospholipid complex. "More absorbable" is one factor among cost, tolerability, and your own needs - there is no single best form for everyone.
- NIH Office of Dietary Supplements - Magnesium, Iron, Zinc, Vitamin D, Folate, Vitamin B12 fact sheets.
- Recker RR. Calcium absorption and achlorhydria. N Engl J Med. 1985;313(2):70–73.
- Dyerberg J, et al. Bioavailability of marine n-3 fatty acid formulations (triglyceride vs ethyl ester). Prostaglandins Leukot Essent Fatty Acids. 2010;83(3):137–141.
- Shoba G, et al. Influence of piperine on the pharmacokinetics of curcumin. Planta Med. 1998;64(4):353–356.
- Tripković L, et al. Comparison of vitamin D2 and D3 supplementation in raising serum 25(OH)D. Am J Clin Nutr. 2012;95(6):1357–1364.
Why the form changes everything.
A label can say "Magnesium 500 mg" and mean 500 mg of magnesium oxide - a form that is cheap, high in magnesium by weight, but poorly absorbed. A different product might list 150 mg of magnesium as bisglycinate, a chelated form that is well absorbed and gentle for most people. The first number looks bigger; the second often delivers more usable magnesium.
Elemental amount is the number that counts
Minerals are sold as compounds - magnesium bound to glycine, zinc bound to picolinic acid, and so on. Only part of that compound's weight is the mineral itself (the "elemental" amount). An honest label tells you the elemental amount. If it only shows the compound weight, you can't tell how much mineral you're actually getting.
What this tool isn't
It's general education about ingredient forms, not a recommendation of what to take or a claim that any form treats anything. For personal choices, talk to a healthcare provider.