Term

Bioavailability

The fraction of a dose that reaches the bloodstream unchanged. The reason a milligram figure on a label cannot be read as a dose.

Bioavailability is the proportion of an administered dose that reaches systemic circulation in an unchanged form. A compound with 50% bioavailability delivers half its dose to the bloodstream; one with 1% delivers almost none.

Why it decides whether a label means anything

Supplement labels state the amount in the capsule, not the amount that arrives. For most vitamins the two are close enough that the distinction does not matter. For a long list of botanicals it matters enormously.

Berberine is the clearest example in this category: in vivo studies report less than 1% oral bioavailability. A trial dosing 900–1,500 mg per day was dosing a compound that largely stayed in the gut. That does not make the trial wrong. It means the milligram figure and the measured effect are connected only through the absorption pathway, and a product that ignores the pathway cannot claim the effect by matching the number.

Three ways products respond to the problem

Absorption enhancers. Sodium caprate, chitosan, and lipid-based carriers are used to increase uptake. These are real strategies with published pharmacokinetic data.

Formulation changes. Microemulsions, nanoparticles, and phytosome complexes alter where and how fast the compound is absorbed.

Nothing. A plain powder at a high milligram count, with the number doing the persuading.

Only the first two can be checked against a trial, and only if the label names the mechanism. “Enhanced absorption” without a named technology is not a specification, and there is no way to verify it from outside.

The related problem: quality

Bioavailability assumes the labelled amount is present. Testing conducted in the United States and France found that berberine supplements frequently did not contain the labelled quantity at all, which means the dose question is preceded by a more basic one: is the ingredient in the bottle.

Third-party testing certificates speak to this, and only this. They do not establish that the product absorbs well, and they do not establish that it works.

What to ask of a label

If a product makes an absorption claim, look for the named technology and, ideally, a pharmacokinetic reference. If it prints a high milligram figure with no absorption discussion, treat the figure as the amount swallowed rather than the amount delivered — which is exactly how the trials treated theirs.