A Caco-2 study is a laboratory test that grows a layer of human intestinal-type cells and measures how well a compound crosses that cell layer — used to estimate how absorbable a substance might be. It's a widely accepted screening tool, but it is an in-vitro (cell-culture) test, not a measurement of what happens in a living person. That distinction is the key to reading any Caco-2 result, including THREE International's.
What the test actually is
Caco-2 cells are a line derived from a human colon cancer. When grown on a porous membrane, they spontaneously form a single layer that behaves in some important ways like the lining of your small intestine. Researchers put a compound on one side of that layer and measure how much crosses to the other side over time. The result — a permeability figure — is used to predict how well the compound might be absorbed in the gut.
It's a genuinely established method. Pharmaceutical companies have used the Caco-2 assay for decades to screen drug candidates, and regulators reference it in absorption guidance. For many compounds, Caco-2 permeability correlates reasonably well with the fraction actually absorbed in humans. So when a supplement company runs one, they are using a real scientific tool, not inventing a metric.
What it measures — and what it doesn't
| Caco-2 CAN indicate | Caco-2 does NOT show |
|---|---|
| Relative permeability across an intestinal-type cell layer | What actually happens in a living human body |
| A useful ranking of how absorbable compounds are | A guaranteed real-world absorption percentage |
| Whether a delivery format improves cell-layer crossing | Whether that translates to a clinical benefit you'll feel |
The model has documented limits: Caco-2 monolayers lack the mucus layer of a real gut, can have tighter cell junctions than human intestine, and only partly replicate the active transport and metabolism that happen in a living person. That's why scientists treat Caco-2 as a screening and ranking tool, not a final answer.
Sources: Caco-2 permeability method and in-vitro–in-vivo correlation literature (Artursson & Karlsson 1991; regulatory ADME reviews, 2013); analyses of Caco-2 limitations for mucus, tight junctions, and active transport (2025).
How to read THREE International's Caco-2 results
THREE commissioned a Caco-2 study reporting its products absorb between roughly 3 and 9.5 times more than the standard organic control molecule used as a baseline in that assay. Read fairly, here is what that means and doesn't mean:
- It means: in that laboratory test, THREE's formulations crossed the cell layer several times more efficiently than an unenhanced control compound. That's a legitimate result and consistent with the idea that delivery format affects absorption.
- It does not mean: you will absorb "9.5 times more" of a nutrient in your body, or that any specific health outcome is guaranteed. The comparison is against a deliberately poorly-absorbed control, in cells, not against every alternative product in a person.
For the full picture of how absorption works and where delivery technology genuinely helps, see the complete cellular absorption guide.