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Does drinking carrot juice affect cancer of the prostate?

MJA 2001; 174: 197

Clinical question - Search question - Search - Summary of findings - Outcome - References

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Question MarkClinical question

"Does drinking carrot juice have any effect on prostate cancer?" A general practitioner asked this question after her patient, a 77-year-old man who had been diagnosed with invasive prostate cancer, commenced drinking four glasses of carrot juice a day. Information about the exact staging of the cancer was not available.

Jigsaw puzzleSearch question

The search question was refined to "What effect does the consumption of beta-carotene have on prostate cancer? Are there any adverse effects, and if so, at what quantity of consumption do they occur?". Ideally, a randomised controlled trial of men recently diagnosed with prostate cancer, comparing a high intake of beta-carotene with no beta-carotene intake, would be the appropriate clinical study design to answer this question. The outcomes assessed would be the appearance of metastases, patient morbidity and mortality, and any adverse effects of the beta-carotene.

Magnifying GlassSearch

The search terms "beta-carotene", "prostate" and "cancer" were combined to identify appropriate trials. We searched databases including Cochrane Library and SUMSearch (<http://sumsearch.uthscsa.edu/searchform4.htm>), which searches for systematic reviews and original research, and links to PubMed Clinical Queries. Our search yielded five relevant studies.

Light bulbSummary of findings

  • The best evidence identified was a large randomised controlled trial of 29 133 healthy men who were cigarette smokers.1 The men receiving beta-carotene (20 mg) daily had an increased incidence of prostate cancer compared with those receiving placebo (138 v 112 men with prostate cancer). Further analysis of the results showed prostate cancer incidence to be 23% higher (95% CI, -4% to 59%) and mortality 15% higher (95% CI, -30% to 89%) in men who received beta-carotene compared with those who did not, but this trend was not significant.2

  • A prospective cohort study found no evidence of either protection or harm associated with dietary beta-carotene.3

  • Two case-control studies, one involving beta-carotene supplements and the other dietary beta-carotene, found a protective effect of high levels of beta-carotene intake.4,5 One of these studies reported a significant protective effect of high levels of dietary beta-carotene (relative risk of prostate cancer [RR], 0.60; 95% CI, 0.37 to 0.99), particularly in men younger than 68 years (RR, 0.30; 95% CI, 0.13 to 0.66).5

We were unable to find any studies evaluating the influence of beta-carotene in patients with established prostate cancer.

KeyOutcome

Although two observational studies suggested that high levels of beta-carotene intake reduced the risk of prostate cancer, the best evidence found that beta-carotene increased the incidence of prostate cancer.

The GP discussed this information with her patient, who nevertheless elected to continue to drink lots of carrot juice!

Christopher B Del Mar
Professor

Paul P Glasziou
Associate Professor

Anneliese B Spinks
Research Officer

Sharon L Sanders
Research Officer
Centre for General Practice
Medical School, University of Queensland, Herston, QLD
c.delmarATcgp.uq.edu.au

References

  1. Albanes D, Heinonen OP, Huttunen JK, et al. Effects of alpha-tocopherol and beta-carotene supplements on cancer incidence in the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study. Am J Clin Nutr 1995; 62 (6 Suppl): 1427S-1430S.
  2. Heinonen OP, Albanes D, Virtamo J, et al. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J Natl Cancer Inst 1998; 90: 440-446.
  3. Daviglus ML, Dyer AR, Persky V, et al. Dietary beta-carotene, vitamin C, and risk of prostate cancer: results from the Western Electric Study. Epidemiology 1996; 7: 472-477.
  4. Gann PH, Ma J, Giovannucci E, et al. Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis. Cancer Res 1999; 59: 1225-1230.
  5. Mettlin C, Selenskas S, Natarajan N, Huben R. Beta-carotene and animal fats and their relationship to prostate cancer risks. A case-control study. Cancer 1989; 64: 605-612.

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