Bioavailability Explained: Why Two Identical-Looking Supplements Can Differ 10x

Two supplements can carry the same milligram count, the same ingredient name, and almost identical packaging — and deliver radically different amounts of active compound into the bloodstream. The published literature on absorption shows differences of two-fold, ten-fold, and in extreme cases nearly two-hundred-fold between formulations of nominally identical ingredients. This is what nutrition pharmacology calls bioavailability, and it is one of the more under-explained ideas in the supplement aisle. **Disclaimer.** Nutripedia summarises published research. We do not provide medical advice. This article is an educational explainer, not a recommendation to take, change, or stop any supplement. Consult a UK GP, NHS pharmacist, or registered dietitian before starting any supplement, especially if pregnant, breastfeeding, on prescription medication, or managing a chronic condition. The practical question this article is built around is simple: when you compare two products on the same shelf, what does the published research say about why one might deliver more of the active ingredient to your bloodstream than the other? We work through six well-studied examples — vitamin D3 vs D2, CoQ10 ubiquinone vs ubiquinol, curcumin and the Meriva phytosomal data, iron bisglycinate vs sulfate, micronised creatine, and magnesium oxide vs glycinate — and finish with a checklist for reading an absorption claim critically.