Question: Cranberry Juice and Bladder Infections SOURCE: "Juice does prevent infection" (9 March 1994), Davis (CA) Enterprise, p. A9. Reprinted with permission. CHICAGO (AP)-A scientific study has proven what many women have long suspected: Cranberry juice helps protect against bladder infections. Researchers found that elderly women who drank 10 ounces of a juice drink containing cranberry juice each day had less than half as many urinary tract infections as those who consumed a look-alike drink without cranberry juice. The study, which appeared today in the Journal of the American Medical Association, was funded by Ocean Spray Cranberries, Inc., but the company had no role in the study's design, analysis or interpretation, JAMA said. "This is the first demonstration that cranberry juice can reduce the presence of bacteria in the urine in humans," said lead researcher Dr. Jerry Avorn, a specialist in medication for the elderly at Harvard Medical School. Discussion This study was well conducted, and the newspaper report is very good, including information such as the source of the funding and the fact that there was a placebo ("a look-alike drink without cranberry juice"). A few details are missing from the news account, however, that you may consider to be important. They are contained in the original report (Avorn et al., 1994):
1. There were 153 subjects.
2. The participants were randomly assigned to the cranberry or placebo group.
3. The placebo was fully described as "a specially prepared synthetic placebo drink that was indistinguishable in taste, appearance, and vitamin C content, but lacked cranberry content."
4. The study was conducted over a 6-month period, with urine samples taken monthly.
5. The measurements taken were actually bacteria counts from urine, rather than a more subjective assessment of whether an infection was present. The news story claims "less than half as many urinary tract infections," but the original report gave the odds of bacteria levels exceeding a certain threshold. The odds in the cranberry juice group were only 42% of what they were in the control group. Unreported in the news story is that the odds of remaining over the threshold from one month to the next for the cranberry juice group were only 27% of what they were for the control group.
6. The participants were elderly women volunteers with a mean age of 78.5 years and high levels of bacteria in their urine at the start of the study.
7. The original theory was that if cranberry juice was effective, it would work by increasing urine acidity. That was not the case, however. The juice inhibited bacterial growth in some other way.