Anti-oxidant supplements and cancer

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JAMA-EXPRESSEditorialRandomized Trials of Antioxidant Supplementation for Cancer Prevention.First Bias, Now Chance—Next, Cause. H. Gann.JAMA. 2009;301(1):(doi:10.1001/jama.2008.863). http://jama.ama-assn.org/cgi/content/full/2008.863

JAMA-EXPRESSVitamins E and C in the Prevention of Prostate and Total Cancer in MenThe Physicians' Health Study II Randomized Controlled Trial J. Gaziano, MD, MPH; J. Glynn, ScD; G. Christen, ScD; Tobias Kurth, MD, ScD; Charlene Belanger, MA; MacFadyen, BA; Vadim Bubes, PhD; JoAnn E. Manson, MD, DrPH; D. Sesso, ScD, MPH; E. Buring, ScD JAMA. 2009;301(1):(doi:10.1001/jama.2008.862). http://jama.ama-assn.org/cgi/content/full/2008.862

JAMA-EXPRESSEffect of Selenium and Vitamin E on Risk of Prostate Cancer and Other CancersThe Selenium and Vitamin E Cancer Prevention Trial (SELECT) M. Lippman, MD; A. Klein, MD; Phyllis J. Goodman, MS; M. Lucia, MD; Ian M. , MD; G. Ford, MD; L. Parnes, MD; Lori M. Minasian, MD; J. Gaziano, MD, MPH; Jo Ann Hartline, MPH; J. Kellogg Parsons, MD, MHS; D. Bearden III, MD; E. Crawford, MD; E. Goodman, MD; Claudio, MD; Winquist, MD, MSc; Elise D. Cook, MD; D. Karp, MD; Philip Walther, MD; M. Lieber, MD; Alan R. Kristal, DrPH; Amy K. Darke, MS; B. Arnold, MS; A. Ganz, MD; Regina M. Santella, PhD; Demetrius Albanes, MD; Philip R. , MD, ScD; L. Probstfield, MD; T. J. Jagpal, CCRP; J. Crowley, PhD; L. Meyskens Jr, MD; ce H. Baker, DO; A. Coltman Jr, MD JAMA.

2009;301(1):(doi:10.1001/jama.2008.864).http://jama.ama-assn.org/cgi/content/full/2008.864

http://www.reuters.com/article/healthNews/idUSTRE4BT50T20081230

Lin, R. Cook, Albert, Elaine Zaharris, J. Gaziano, Van Denburgh, E. Buring, and JoAnn E. MansonVitamins C and E and Beta Carotene Supplementation and Cancer Risk: A Randomized Controlled TrialJ Natl Cancer Inst, Advance Access published on December 30, 2008; doi: doi:10.1093/jnci/djn438

Background: Observational studies suggested that a diet high in fruits and vegetables, both of which are rich with antioxidants, may prevent cancer development. However, findings from randomized trials of the association between antioxidant use and cancer risk have been mostly negative.

Methods: From 8171 women who were randomly assigned in the Women's Antioxidant Cardiovascular Study, a double-blind, placebo-controlled 2 x 2 x 2 factorial trial of vitamin C (500 mg of ascorbic acid daily), natural-source vitamin E (600 IU of -tocopherol every other day), and beta carotene (50 mg every other day), 7627 women who were free of cancer before random assignment were selected for this study. Diagnoses and deaths from cancer at a specific site were confirmed by use of hospital reports and the National Death Index. proportional hazards regression models were used to assess hazard ratios (represented as relative risks [RRs]) of common cancers associated with use of antioxidants, either individually or in combination. Subgroup analyses were conducted to determine if duration of use modified the association of supplement use with cancer risk. All statistical tests were two-sided.

Results: During an average 9.4 years of treatment, 624 women developed incident invasive cancer and 176 women died from cancer. There were no statistically significant effects of use of any antioxidant on total cancer incidence. Compared with the placebo group, the RRs were 1.11 (95% confidence interval [CI] = 0.95 to 1.30) in the vitamin C group, 0.93 (95% CI = 0.79 to 1.09) in the vitamin E group, and 1.00 (95% CI = 0.85 to 1.17) in the beta carotene group. Similarly, no effects of these antioxidants were observed on cancer mortality. Compared with the placebo group, the RRs were 1.28 (95% CI = 0.95 to 1.73) in the vitamin C group, 0.87 (95% CI = 0.65 to 1.17) in the vitamin E group, and 0.84 (95% CI = 0.62 to 1.13) in the beta carotene group. Duration and combined use of the three antioxidants also had no effect on cancer incidence and cancer death.

Conclusions: Supplementation with vitamin C, vitamin E, or beta carotene offers no overall benefits in the primary prevention of total cancer incidence or cancer mortality.

From the Editors

CONTEXT AND CAVEATS

Prior knowledge

Although some observational studies suggest that a diet high in fruits and vegetables and thus antioxidants may be associated with a reduced risk of cancer, randomized trials have not supported this association.

Study design

Randomized controlled trial using a factorial design with hazard ratios from regression models to compare intervention effects.

Contribution

This study, which was designed to have 80% power to detect a 30% reduction in the overall risk of cancer, suggests that long-term dietary supplementation with any combination of the antioxidants vitamin C, vitamin E, or beta carotene does not reduce the risk of cancer or the risk of dying from cancer.

Implications

There is no basis for a recommendation that individuals increase dietary levels of antioxidants as a means of reducing cancer risk.

Limitations

This study had very limited statistical power to investigate any effect of dietary antioxidants on the risk of specific cancers.

-- Al Pater, alpater@...