Cranberries may be protective against urinary tract infection

Cranberry products probably do help prevent urinary tract infections, according to a meta-analysis of 13 randomised trials. A significant effect emerged from pooled analyses that excluded one outlying trial (risk ratio 0.62, 95% CI 0.49 - 0.80), confirming results from a previous much smaller meta-analysis.

Juice seemed to work best in subgroup analyses (0.47, 0.30 - 0.72), although only 4 of 13 trials tested non-juice products such as capsules or tablets. Cranberry products protected women with recurrent infections, children and anyone taking more than 2 doses a day. Results for older adults, pregnant women and people with neuropathic bladders were less clear-cut. The trials had limitations, including a tendency for participants to drop out before completing their treatment. They weren’t well reported and tested a wide range of doses. Results are encouraging but not definitive, say the authors.

Cranberries (genus Vaccinium) have been used as a natural remedy for at least 100 years, and in the 1980s scientists discovered that the berries contain an active ingredient (possibly proanthocyanidins) that stops bacteria sticking to uro-epithelial cells. Future trials might usefully test different doses of cranberry and specify proanthocyanidin content from the outset. Many other potentially active ingredients are waiting to be investigated.

Wang C-H, et al. Arch Intern Med 2012;172:988-996.