Cranberry juice really does prevent bladder infections,” reports the Mail Online, suggesting that it’s “not an old wives’ tale” after all.

But the piece of research this story is based on only tested the effects of cranberries in the laboratory and not in humans. Crucially, human studies can differ from laboratory findings. The research found that cranberry powder made from whole cranberries had antibiotic properties against a bacterium called Proteus mirabilis, one of the common causes of urinary tract infections (UTIs).

The powder used in the research disrupted the movement of the bacteria (motility). It also inhibited the production of an enzyme called urease, thought to be key to the bacteria’s virulence (its ability to cause illness).

Previous research found a small trend towards fewer UTIs in people taking cranberry products. However, this was not a statistically significant finding, meaning it may have been down to chance, and many people in these studies stopped drinking the juice early, suggesting it may not be an acceptable intervention.

This research adds to the biological understanding of a specific bacteria involved in some UTIs and the potential antibiotic role of cranberries, but it does not prove that cranberries prevent bladder infections in people. Other, more robust evidence that looked at this directly found that the effect is either very small or non-existent.