Cranberry

What is cranberry?

Cranberry is the fruit of Vaccinium macrocarpon, the American species, with a European relative, Vaccinium oxycoccos, picked as well. It brings anthocyanins, flavonols and phenolic acids, but what sets it apart is the kind of proanthocyanidin it carries: the A-type, where most fruit carries the B-type. It is sold as juice, as dried whole-fruit powder of peel, seeds and pulp, and as concentrated extracts in capsules and tablets, some of which state the milligrams of proanthocyanidin per serving. In Britain it is bought above all by women who keep getting urinary infections.

Why do people take cranberry?

What does cranberry do in the body?

Cranberry is not a nutrient, and the body has no job waiting for it. What it brings is polyphenols, and one group in particular: proanthocyanidins built with what chemists call A-type bonds, the shape that marks cranberry out. Reviewers describe these compounds as antimicrobial, antiadhesive, antioxidant and anti-inflammatory.

In the urinary tract the proposed mechanism is stickiness. Escherichia coli holds on to the cells lining the bladder with fine threads, and cranberry’s proanthocyanidins are described as getting in the way of that grip, so bacteria are carried out rather than settling in. Reviewers are candid that the picture is incomplete, and that results vary partly because trials used many different products whose content was often never measured, at different doses and for different lengths.

What do people say about taking cranberry?

These are anecdotes people have shared, not evidence.

What forms of cranberry are there?

What else is worth knowing about cranberry?

• Across ten trials in 2,166 people the largest review found stomach and bowel side effects no more common than on a dummy. Its earlier version noted that many trials lost people along the way, blaming the palatability of the products, the juice above all.
• The 2023 review reports a lower risk in women with recurrent infections, in children, and in people made susceptible by a procedure, but not in elderly people in institutions, in pregnancy, or in adults who do not empty the bladder fully.
• A separate review looked for trials of cranberry against an infection already under way and found none that met its criteria, so there is nothing to report there.
• Labels give the amount in a serving, which may be more than one capsule, and the figure to compare is the proanthocyanidin content, not the weight of extract. Trials have used 18.5 mg twice a day and two capsules of 36 mg.
• Much of the work used juice, a drink rather than a supplement: the beverage in one trial carried 173 mg of phenolic compounds and 6.5 g of sugar in a 240 ml serving.

If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.