Efficacy of Cranberry Products in Urinary Tract Health
Updated March 22, 2017
On March 14, 2017, JAMA published a letter to the editor written by researchers at McGill University in response to the misleading research study published in JAMA regarding cranberries’ ability to effectively prevent UTIs.
In the letter, the researchers state that due to two major features of the study’s methodology, the results should be considered “less than definitive.” Of note:
- “About two-thirds of the woman participating in the study had not had a UTI in the year preceding the trial”
- “The sample size was small, and the rate of withdrawals and missing urine tests was high”
The full letter can be read here.
October 28, 2016
Statement from the Cranberry Institute
The Cranberry Institute maintains its confidence in the decades of scientific studies from independent research institutions globally, that have demonstrated that regular consumption of cranberry products helps promote a healthy urinary tract – especially in individuals suffering from recurrent UTIs.1,2
The Journal of the American Medical Association (JAMA) article, “Effect of Cranberry Capsules on Bacteriuria Plus Pyuria Among Older Women in Nursing Homes” and the subsequent editorial piece, “Cranberry for Prevention of Urinary Tract Infection? Time to move on” is misleading and suffers from fatal flaws. The investigation fails to assess the efficacy of cranberries in the prevention of recurrent urinary tract infections (UTIs) as they treated individuals that did NOT suffer from UTIs or persistent bacteriuria plus pyuria. We are disappointed that this venerated journal supported the publication of the trial and utilized it as a platform to selectively discredit previously peer-reviewed data.
Investigations that aim to assess the efficacy of cranberry products in the prevention of UTIs and maintenance of urinary tract health is a critical priority of the Cranberry Institute. And the benefits for elderly women in nursing homes is a key concern. However, in this particular study, participants were treated with cranberry capsules for issues that did not exist (see tables from the study below). It is likened to evaluating the effectiveness of a weight loss program on individuals with normal body weight – the absence of weight loss will not truly reflect the efficacy of the program.
We agree with the author of the editorial that it is important to identify and evaluate innovative antimicrobial and non-antimicrobial approaches – and encourage the cranberry scientific community to continue this quest. It is time to move forward by furthering cranberry research to help attenuate the use of antibiotics and prevent this pervasive condition.
For a comprehensive reference list of cranberry health research, visit: http://cranberryinstitute.org/doclib/doclib_search.cgi.
Key Research Inaccuracies
- The results of this study are not valid or reliable – the efficacy of cranberry products cannot be determined based on significant confounding methodological issues.
- The most glaring deficiency in methodology is the choice to study patients who do not suffer from recurrent UTIs. It is like treating individuals who do NOT have a headache with a common headache remedy to prove or disprove the treatment’s effectiveness. The results will not show if the treatment was effective.
- In addition to this fatal flaw, the results are further misleading due to:
- The presence of asymptomatic bacteriuria in the urine of an elderly woman does not mean that they have a UTI.
- Of the 185 patients enrolled, 78% had dementia, 59% of patients had 1-8 ADL disabilities, 16% resist care and 7% are not alert. Furthermore, there were 68% urinary incontinence and 44 % bowel incontinence rates. These patients cannot give a reliable urine sample without contamination, as frequently experienced in a clinical situation.
- There was no indication of how compliance was measured.
- Howell AB. Cranberry proanthocyanidins and the maintenance of urinary tract health. Crit Rev Food Sci Nutr. 2002;42(3 Suppl):273-8.
- Blumberg JB, et al. Cranberries and their bioactive constituents in human health. Adv Nutr. 2013;4:1–15.
- Wang, et al. Cranberry-Containing Products for Prevention of Urinary Tract Infections in Susceptible Populations: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Arch Intern Med. 2012;172(13):988-996. doi:10.1001/archinternmed.2012.3004.
- Takahashi, et al. A randomized clinical trial to evaluate the preventive effect of cranberry juice (UR65) for patients with recurrent urinary tract infection. Journal of Infection and Chemotherapy. 2013;19(1):112-7.
- Sobota AE. Inhibition of bacterial adherence by cranberry juice: potential use for the treatment of urinary tract infection. J Urol. 1984;131(5):1013-6.
- Avorn J, Monane M, Gurwitz JH, Glynn RJ, Choodnovskiy I, Lipsitz LA. Reduction of bacteriuria and pyuria after ingestion of cranberry juice. JAMA. 1994;271(10):751-754.
- Avorn J. The effect of cranberry juice on the presence of bacteria and white blood cells in the urine of elderly women. What is the role of bacterial adhesion? Adv Exp Med Biol. 1996;408:185-6.
- Fleet JC. New support for a folk remedy: cranberry juice reduces bacteriuria and pyuria in elderly women. Nutr Rev. 1994;52(5):168-70.
- Ahuja S, Kaack B, Roberts J. Loss of fimbrial adhesion with the addition of Vaccinum macrocarpon to the growth medium of P-fimbriated Escherichia coli. J Urol. 1998;159(2):559-62.