BioPerine®
Black pepper fruit extract at 5 mg. It raises the bioavailability of co-taken compounds, including curcumin and iron, and 5 mg is the studied amount.
Written by R. Kessler · About Knurle · Editorial policy
The short answer
BioPerine is a standardised black pepper fruit extract containing piperine. Piperine inhibits enzymes and transporters that would otherwise break down or limit the absorption of co-taken compounds, which raises their bioavailability. The studied supplemental dose is around 5 to 20 mg a day.
The form, and why it matters
A standardised fruit extract rather than ground black pepper, because the dose of piperine in culinary pepper is trivial by comparison and impossible to standardise.
Typical dose
The published human work sits around 5 to 20 mg of piperine a day. Keel carries 5 mg, at the low end, which is the amount the co-taken iron studies used.
What the research shows
Studies of iron co-administered with piperine showed higher serum iron than iron alone, and human work in iron-low people improved haemoglobin and ferritin. The same mechanism raises curcumin bioavailability substantially, which is why piperine appears in most curcumin formulas.
Who should be careful
Piperine increases the absorption of several medicines by the same mechanism that helps nutrients, including some blood pressure drugs and sedatives. If you take prescription medication, check with a pharmacist before adding it.
Where it sits in our formulas
| Product | Form on the label | Amount per serving | % Daily Value |
|---|---|---|---|
| Keel | black pepper fruit | 5 mg | not established |
Sources
Figures checked against the sources above on 21 September 2026.
Iron
Ferrous bisglycinate at 18 mg, a chelated form that is usually kinder to the stomach than oxide or sulfate at the same elemental amount.
Read itMagnesium
200 mg as oxide plus citrate. Magnesium draws water into the bowel, which is why the oxide form is the one that helps constipation.
Read itFerrous bisglycinate: the iron that is gentle
Why Keel uses 18 mg ferrous bisglycinate plus 5 mg BioPerine rather than a cheap oxide. What black stool actually means, why with food, and when to check ferritin instead of guessing.
Read itHow to read a supplement label
How to read a supplement label in ninety seconds: serving sizes, % Daily Value, ingredient forms, and where the useful numbers live.
Read itEvery milligram, printed.
Each amount on the label is the amount in a full daily serving, and it matches what is on this page.
