Ericaceae
Vaccinium macrocarpon
Cranberry · American cranberry
- Part used
- fruit
- Native range
- Bogs and wet acidic ground of northeastern North America
- Morphology
- A low creeping evergreen shrub of acid bog, with small leathery leaves, pink reflexed flowers said to resemble a crane, and firm red berries with internal air pockets that let them float — which is how they are harvested.
What is in it
Evidence
One of the better-studied traditional foods and a genuinely instructive result. Cochrane reviewed cranberry for preventing urinary tract infection repeatedly and downgraded its conclusion over time as larger trials arrived — the 2012 review concluded the benefit was too small to justify recommendation, while a 2023 update found a modest reduction in recurrent UTI in some groups. It is not a treatment for an established infection.
Safety
A food. High oxalate content matters for kidney stone formers. Cranberry juice is high in sugar unless unsweetened.
Interactions: Reported potentiation of warfarin, with case reports of raised INR
Regulatory: Permitted as a food and as a listed medicine ingredient.
Historical use
Eaten by Algonquian peoples and used as food, dye and in wound poultices. Adopted by colonists and commercialised in the nineteenth century. The urinary use is comparatively recent.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
Cranberry is the clearest example in this collection of a mechanism being right and the clinical benefit being smaller than everyone assumed.
The mechanism is real and specific: A-type proanthocyanidins interfere with the adhesion of E. coli fimbriae to the bladder wall, and that is demonstrable in the laboratory. The old folk explanation — that cranberry acidifies the urine — is wrong, and the actual mechanism is more interesting.
What the trials show is that a real anti-adhesion effect translates into a modest reduction in recurrent infections in some groups, and nothing at all for treating an infection already established. The Cochrane conclusion has moved back and forth as trials accumulated, which is what an honest evidence base looks like when the effect is small.
Nomenclature verified against GBIF backbone taxonomy.