What does absorption mean?
Absorption is the uptake of a substance from the gut into the blood. Only what is absorbed can act in the rest of the body. For curcumin, absorption is low because it dissolves poorly in water; fat in the meal helps.
Absorption explained simply
When you swallow a capsule, its contents are first only in the digestive tract, not yet “in the body”. To reach the blood, they must cross the intestinal wall. This process is called absorption (in everyday speech, uptake in the gut). It takes place mainly in the small intestine, whose surface area is very large thanks to folds and villi.
The substance first has to dissolve in the intestinal fluid, then cross the intestinal wall, either by diffusion or via transport proteins, and finally reaches the liver via the portal vein.
Absorption and bioavailability
The two terms are often mixed up. Absorption describes uptake from the gut. Bioavailability goes one step further: it states what share actually arrives unchanged in the bloodstream after breakdown in the gut wall and liver (the first-pass effect) has been subtracted.
What absorption depends on
Factors that influence how much is taken up from the gut.
| Factor | Effect |
|---|---|
| Factor Solubility | Effect what does not dissolve is barely absorbed |
| Factor Fat in the meal | Effect promotes uptake of fat-soluble compounds via bile acids and micelles |
| Factor Molecular size and charge | Effect determine whether a substance can cross the gut wall |
| Factor Transport proteins | Effect can carry compounds into the cell or pump them back out |
| Factor Formulation | Effect can deliberately improve solubility and uptake |
Absorption of curcumin
Curcumin is strongly lipophilic and hardly dissolves in water. In addition, it is broken down rapidly after uptake. Ordinary curcumin therefore reaches only very low blood levels. Fat in the meal improves absorption, but only to a limited extent.
Technical solutions start with solubility. One example is the inclusion complex with γ-cyclodextrin used in Curcumin+: there, curcumin is present in water-soluble form. In a small pilot study of a γ-cyclodextrin formulation (12 healthy adults, double-blind, crossover, single dose), about 39 times more total curcuminoids and about 85 times more curcumin in the blood (AUC, dose-normalised) were found compared with an unformulated, standardised curcumin extract. The study tested another manufacturer's commercial product made by a different process. Curcumin+ is made by the kneading method; there is no absorption study of Curcumin+ itself, so these figures cannot be transferred directly. That describes uptake, not a health effect.
Common mix-up: resorption and absorption
In German medicine, Resorption denotes uptake into the body, which corresponds to “absorption” in English. In German pharmacokinetics, “Resorption” and “Absorption” are used synonymously; “Resorption” is the more common term in German medical usage for uptake of nutrients and active compounds from the gut. Outside medicine, “Absorption” also means soaking up, such as of light.
Uptake through the skin or mucous membranes is also called absorption. Intestinal absorption, however, is the normal case for capsules and food.
Frequently asked questions
Where does absorption take place? Mainly in the small intestine. Some substances, such as alcohol or certain medicines, are partly taken up already through the stomach or oral mucosa.
Does fat improve absorption? For fat-soluble compounds such as curcumin and vitamins A, D, E and K, yes, because bile acids and micelles carry them.
Can I improve absorption? By taking with a meal and through suitable formulations. For medication, ask your pharmacist about timing.
What counts is not the amount in the capsule but the amount that is absorbed. Two products with the same dose can end up very differently in the blood.
