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Meta-Analysis
. 2011 May 11:(5):CD005195.
doi: 10.1002/14651858.CD005195.pub2.

Selenium for preventing cancer

Gabriele Dennert  1 , Marcel Zwahlen, Maree Brinkman, Marco Vinceti, Maurice P A Zeegers, Markus Horneber
Affiliations
Meta-Analysis

Selenium for preventing cancer

Gabriele Dennert et al. Cochrane Database Syst Rev. .

Update in

Abstract

Background: Selenium is a trace element essential to humans. Higher selenium exposure and selenium supplements have been suggested to protect against several types of cancers.

Objectives: Two research questions were addressed in this review: What is the evidence for1. an aetiological relationship between selenium exposure and cancer risk in women and men?2. the efficacy of selenium supplementation for cancer prevention in women and men?

Search strategy: We searched electronic databases and bibliographies of reviews and included publications.

Selection criteria: We included prospective observational studies to answer research question (a) and randomised controlled trials (RCTs) to answer research question (b).

Data collection and analysis: We conducted random effects meta-analyses of epidemiological data when five or more studies were retrieved for a specific outcome. We made a narrative summary of data from RCTs.

Main results: We included 49 prospective observational studies and six RCTs. In epidemiologic data, we found a reduced cancer incidence (summary odds ratio (OR) 0.69 (95% confidence interval (CI) 0.53 to 0.91) and mortality (OR 0.55, 95% CI 0.36 to 0.83) with higher selenium exposure. Cancer risk was more pronouncedly reduced in men (incidence: OR 0.66, 95% CI 0.42 to 1.05) than in women (incidence: OR 0.90, 95% CI 0.45 to 1.77). These findings have potential limitations due to study design, quality and heterogeneity of the data, which complicated the interpretation of the summary statistics.The RCTs found no protective efficacy of selenium yeast supplementation against non-melanoma skin cancer or L-selenomethionine supplementation against prostate cancer. Study results for the prevention of liver cancer with selenium supplements were inconsistent and studies had an unclear risk of bias. The results of the Nutritional Prevention of Cancer Trial (NPCT) and SELECT raised concerns about possible harmful effects of selenium supplements.

Authors' conclusions: No reliable conclusions can be drawn regarding a causal relationship between low selenium exposure and an increased risk of cancer. Despite evidence for an inverse association between selenium exposure and the risk of some types of cancer, these results should be interpreted with care due to the potential limiting factors of heterogeneity and influences of unknown biases, confounding and effect modification.The effect of selenium supplementation from RCTs yielded inconsistent results. To date, there is no convincing evidence that selenium supplements can prevent cancer in men, women or children.

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Conflict of interest statement

DECLARATIONS OF INTEREST

GD: None known

MZw: None known

MB: None known

MV: None known

MZe: Maurice Zeegers is the first investigator of one included observational study and one ongoing randomised controlled trial. He is second author of another included observational study.

MH: None known

Figures

Analysis 1.1
Analysis 1.1
Comparison 1 Highest versus lowest selenium exposure, Outcome 1 Breast cancer risk (women).
Analysis 1.2
Analysis 1.2
Comparison 1 Highest versus lowest selenium exposure, Outcome 2 Bladder cancer risk.
Analysis 1.3
Analysis 1.3
Comparison 1 Highest versus lowest selenium exposure, Outcome 3 Lung cancer risk (gender-aggregated data).
Analysis 1.4
Analysis 1.4
Comparison 1 Highest versus lowest selenium exposure, Outcome 4 Lung cancer risk (gender-disaggregated data).
Analysis 1.5
Analysis 1.5
Comparison 1 Highest versus lowest selenium exposure, Outcome 5 Lung cancer risk (ascending order of selenium levels).
Analysis 1.6
Analysis 1.6
Comparison 1 Highest versus lowest selenium exposure, Outcome 6 Lung cancer risk.
Analysis 1.7
Analysis 1.7
Comparison 1 Highest versus lowest selenium exposure, Outcome 7 Prostate cancer risk.
Analysis 1.8
Analysis 1.8
Comparison 1 Highest versus lowest selenium exposure, Outcome 8 Prostate cancer risk (by selenium measurement).
Analysis 1.9
Analysis 1.9
Comparison 1 Highest versus lowest selenium exposure, Outcome 9 Prostate cancer risk (by exposure assessment).
Analysis 1.10
Analysis 1.10
Comparison 1 Highest versus lowest selenium exposure, Outcome 10 Prostate cancer risk (by continent).
Analysis 1.11
Analysis 1.11
Comparison 1 Highest versus lowest selenium exposure, Outcome 11 Prostate cancer risk (by country).
Analysis 1.11
Analysis 1.11
Comparison 1 Highest versus lowest selenium exposure, Outcome 11 Prostate cancer risk (by country).
Analysis 1.12
Analysis 1.12
Comparison 1 Highest versus lowest selenium exposure, Outcome 12 Prostate cancer risk (ascending order of selenium levels).
Analysis 1.13
Analysis 1.13
Comparison 1 Highest versus lowest selenium exposure, Outcome 13 Stomach cancer risk.
Analysis 1.14
Analysis 1.14
Comparison 1 Highest versus lowest selenium exposure, Outcome 14 Stomach cancer risk (by gender).
Analysis 1.15
Analysis 1.15
Comparison 1 Highest versus lowest selenium exposure, Outcome 15 Colorectal cancer risk.
Analysis 1.16
Analysis 1.16
Comparison 1 Highest versus lowest selenium exposure, Outcome 16 Colorectal cancer risk (by gender).
Analysis 1.17
Analysis 1.17
Comparison 1 Highest versus lowest selenium exposure, Outcome 17 Total cancer incidence and mortality.
Analysis 1.18
Analysis 1.18
Comparison 1 Highest versus lowest selenium exposure, Outcome 18 Total cancer incidence and mortality (ascending order of selenium levels).
Analysis 1.19
Analysis 1.19
Comparison 1 Highest versus lowest selenium exposure, Outcome 19 Total cancer incidence and mortality (women).
Analysis 1.20
Analysis 1.20
Comparison 1 Highest versus lowest selenium exposure, Outcome 20 Total cancer incidence and mortality (men).
Figure 1
Figure 1
Flow chart literature search
Figure 2
Figure 2
Newcastle-Ottawa-Scale: number of studies by number of “stars” assigned in the case-control part of studies
Figure 3
Figure 3
Newcastle Ottawa-Scale: number of studies by number of “stars” assigned in the cohort part of studies
Figure 4
Figure 4
Funnel plot of comparison: 1 Highest versus lowest selenium exposure, outcome: 1.17 Total cancer incidence and mortality.
Figure 5
Figure 5
Funnel plot of comparison: 1 Highest versus lowest selenium exposure, outcome: 1.7 Prostate cancer risk.
See this image and copyright information in PMC

Comment in

  • [Does selenium protect against cancer?].
    Adam O. Adam O. Dtsch Med Wochenschr. 2011 Aug;136(34-35):1709. doi: 10.1055/s-0031-1286350. Epub 2011 Aug 29. Dtsch Med Wochenschr. 2011. PMID: 21877300 German. No abstract available.

References

References to studies included in this review

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References to studies excluded from this review

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    2. Eastern Cooperative Oncology Group. ECOG-5597. Phase III randomized chemoprevention study of selenium in participants with previously resected stage I non-small cell lung cancer. Eastern Cooperative Oncology Group; [accessed 6 April 2011]. http://www.cancer.gov/clinicaltrials/featured/trials/ecog-5598.
    3. Karp DD. Phase III chemoprevention trial of selenium supplementation in persons with resected stage I non-small-cell lung cancer. Clinical Advances in Hematology and Oncology. 2005;3(4):313–5.
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    5. Marshall JR, Sakr W, Wood D, Berry D, Tangen C, Parker F, et al. Design and progress of a trial of selenium to prevent prostate cancer among men with high-grade prostatic intraepithelial neoplasia. Cancer Epidemiology, Biomarkers & Prevention. 2006;15(8):1479–84. - PubMed
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