Two numbers describe every supplement, and labels only ever print the first one. The gap between them explains most of the disappointment in this category.
The number on the panel
A supplement facts panel reports the quantity of each ingredient per serving. That figure is about manufacturing: it is what was weighed out and encapsulated, verified against the fill specification.
It is a real number and a useful one. Without it — which is the situation whenever ingredients are pooled into a proprietary blend — you cannot compare a product to the research at all. Named amounts are the floor, not the ceiling, of what a label should tell you.
The number nobody prints
The absorbed dose is how much actually reaches circulation. For some ingredients it tracks the label figure closely. For others it is a small fraction of it, and the fraction moves depending on what else you ate.
Nobody prints it because it is not a fixed property of the product. It depends on the individual, the meal, the form of the extract and the time of day. A manufacturer can report what went in. What comes out is partly yours to influence.
Where the gap is widest
Curcuminoids from turmeric. The largest gap of the six. Poor dissolution, limited transit, and heavy first-pass metabolism compound each other. This is the ingredient where form and food matter most.
Lutein from marigold. Fat-dependent at the dissolution stage, so the gap is wide without a meal and narrows considerably with one. It then has an additional slow stage: accumulation into tissue over months.
Ginkgo's actives. Reasonably absorbed. Here the variable is upstream — whether the extract was standardised at all, which determines how much active compound was in the capsule before absorption became the question.
Green tea catechins and glucosamine. Water-soluble, absorbed without much drama. The panel figure is closer to the useful figure.
How to use this when comparing products
- Check standardisation before milligrams. 120 mg of a standardised extract and 120 mg of powdered leaf are not comparable quantities of anything that matters.
- Check whether the form addresses absorption for the ingredients that need it — and whether the directions tell you to help.
- Work out cost per day, not per bottle, and only after the serving size is clear. A four-capsule serving turns a 120-count bottle into a month.
- Treat an unexplained large dose with mild suspicion. Pushing the label figure up is the cheapest way to look generous without addressing why the compound absorbs badly.
The honest summary
The milligram figure is necessary information and incomplete information. Read it, compare it, and then ask the second question — what proportion of this is realistically going to reach me, and what am I expected to do about it. For two of the six ingredients here, the answer involves breakfast.