Read the original paper first
Robert Cathcart's 1981 article appeared in Medical Hypotheses under the title Vitamin C, titrating to bowel tolerance, anascorbemia, and acute induced scurvy. It describes changes in reported oral vitamin C tolerance across clinical situations. Its table is part of that proposed clinical model, not an established prescribing guideline. [1]
Distinguish oral absorption from an outcome
Oral vitamin C absorption and blood concentrations are regulated. Pharmacokinetic research examines how intake, absorption and excretion relate to circulating concentrations. Tolerance of an amount, a measured concentration and improvement in an illness are different endpoints. Evidence for one endpoint does not automatically establish the others. [2] [3]
Understand what bowel tolerance signifies
Gastrointestinal effects can occur with high vitamin C intakes. Reaching loose stools is an adverse-effect threshold, not proof that a tissue deficiency has been corrected or that an infection is being treated effectively. Cathcart's explanation remains a historical proposal that should be evaluated alongside subsequent evidence. [1] [2]
Use the literature to ask better questions
The original paper is linked below so its language and assumptions can be checked directly. This guide does not reproduce its table as a dosing schedule or instruct readers to escalate intake. Questions about high-dose use, medical conditions and interactions belong in a discussion with an appropriately qualified clinician. [1] [2]
| Marker | Quest example | Labcorp example |
|---|---|---|
| Vitamin C | Serum: male 0.2–2.1; female 0.3–2.7 mg/dL. Assay source ↗ | Plasma: 0.4–2.0 mg/dL. Assay source ↗ |
These notes explain sources and testing context. They do not diagnose a condition, select a personal supplement dose or replace professional medical advice.