Clinical trials of vitamin and mineral supplements for cancer prevention

Our plain-English summary of Clinical trials of vitamin and mineral supplements for cancer prevention, by P. Greenwald, D. Anderson, S.A. Nelson, et al (The American Journal of Clinical Nutrition, 2007).

The study

• Authors: P. Greenwald, D. Anderson, S.A. Nelson, P.R. Taylor
• Journal: The American Journal of Clinical Nutrition
• Published: 2007;85(1):314S-317S
• Type of article: Review
• Cited by: 77 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Approximately 20-30% of Americans consume multivitamin supplements daily, indicating high public interest in the prevention of cancer and other chronic diseases through a nutrition-based approach. Although several bioactive food components, including vitamins and minerals, have been investigated for their ability to affect cancer risk, few large, randomized, placebo-controlled clinical trials of multivitamins with cancer as the primary endpoint have been performed. The results of most large-scale trials of multivitamin supplements (combinations of > or = 2 vitamins and minerals) to prevent cancer have been mixed. The Linxian General Population and Dysplasia trials found a decreased risk of cancer, particularly stomach cancer, for participants taking a multivitamin supplement, but this was in a borderline-deficient population in China. Two trials, the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study and the beta-Carotene and Retinol Efficacy Trial, found an increased risk of lung cancer among male cigarette smokers or asbestos-exposed persons taking beta-carotene-a surprising result, considering that most epidemiologic studies have suggested that consumption of fruit and vegetables appears to lower cancer risk. To clarify the effects of multivitamin supplements, several large randomized clinical trials are underway, including the Physicians' Health Study II, the Selenium and Vitamin E Cancer Prevention Trial, and a European study, Supplémentation en Vitamines et Minéraux Antioxydants (SU.VI. MAX). Because epidemiologic studies generally evaluate foods rather than specific bioactive food components, a systematic approach to determining how combinations of vitamins and minerals may interact to ameliorate cancer risk is necessary to further our understanding of the potential benefits and risks of supplement use.

In plain English

This article reviewed large randomized clinical trials of vitamin and mineral supplements for cancer prevention. It was a conference presentation and reported no new data of its own. The Linxian General Population Trial in China randomly assigned 29 594 adults from a population the authors described as nutritionally marginal. Those who received a beta-carotene, vitamin E and selenium combination had a 13% reduction in cancer mortality. In the ATBC trial of 29 133 male smokers, those who took beta-carotene had a 16% increase in lung cancer incidence. The CARET trial reported a 39% increase in lung cancer incidence among male smokers given beta-carotene and retinyl palmitate. The article's abstract describes these two trials as finding increased lung cancer risk among male cigarette smokers or asbestos-exposed persons taking beta-carotene. The article gave no separate figures for asbestos-exposed people. The review also described the Women's Health Initiative and SU.VI.MAX, and the SELECT and Physicians' Health Study II trials, then still under way. The authors concluded that a more intensive clinical trial research program on multivitamin supplementation was needed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review of selected large randomized clinical trials of vitamin and mineral supplements for cancer prevention (conference presentation)
• Who was studied: Participants in the trials reviewed. These included 29 594 adults aged 40–69 in the Linxian General Population Trial in China, a population the authors described as nutritionally marginal or borderline-deficient, and 29 133 male smokers aged 50–69 in ATBC (Finland). They also included male smokers in CARET and participants in the Women's Health Initiative, SU.VI.MAX, SELECT and the Physicians' Health Studies.
• Exposure: Vitamin and mineral supplements, including beta-carotene, alpha-tocopherol (vitamin E), selenium, retinyl palmitate, calcium and vitamin D, and multivitamin combinations. Asbestos exposure is mentioned only in the abstract, as a characteristic of some trial participants.
• Main results:
  • Linxian General Population Trial, in a nutritionally marginal population in China: participants who received the beta-carotene, vitamin E and selenium combination had a 13% reduction in cancer mortality.
  • The authors described the Linxian benefit as occurring in a borderline-deficient population.
  • ATBC trial (male smokers): men who took beta-carotene had a 16% increase in lung cancer incidence.
  • CARET: a 39% increase in lung cancer incidence among male smokers who received beta-carotene combined with retinyl palmitate.
  • The abstract states that ATBC and CARET found an increased risk of lung cancer among male cigarette smokers or asbestos-exposed persons taking beta-carotene. No figures specific to asbestos-exposed persons are given.
  • SU.VI.MAX: among the 94% of men with lower baseline PSA concentrations, prostate cancer incidence fell by 48% in those who received the supplements (hazard ratio 0.52, 95% CI 0.29 to 0.92).
  • Women's Health Initiative: daily calcium and vitamin D supplementation had no effect on colorectal cancer incidence among postmenopausal women.
• The authors' conclusion: The authors concluded that results of the trials were mixed, and that a more intensive clinical trial research program on multivitamin supplementation for chronic disease prevention was needed.

Topics

Medical terms in this study, explained in our Lexicon: Clinical Trial, Stomach Cancer, Lung Cancer.

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