Meta-analysisindependent cross-checkabstract checked I-SUP-117 standard review

Selenium for preventing cancer: Cochrane review

Selenium for preventing cancer.

Overview

Vinceti M et al.. Cochrane Database Syst Rev 2018 · PMID 29376219 · DOI 10.1002/14651858.CD005195.pub4

Selenium pills did not prevent cancer, and trials hinted at more type 2 diabetes.

Does the study support the specific claim? Yes · Methodological quality: high

Original publication

Plain-language summary

Study explained simply

What did the researchers want to find out?: To test selenium for cancer prevention.
How was the study done?: Cochrane review of trials and cohorts.
How many people, animals or samples were studied?: 10 trials (27,232 people); 70 cohorts.
What was actually found?: No cancer prevention; possible more diabetes and high-grade prostate cancer in some.
How large was the observed effect?: Cancer RR 1.01 (0.93-1.10).
What do the results mean in everyday life?: Selenium pills are not useful for cancer prevention.
What are the study's limitations?: Diabetes risk not quantified here.
What does it say about Elawady's specific claim?: Supports C-SUP-01 and C-SUP-07.
Do the results apply to Germany and Europe?: Applicable.
What can explicitly not be concluded from this study?: Not about selenium-deficient regions.

Scientific in-depth review

1. Full reference

Authors: Vinceti M et al.
Journal: Cochrane Database Syst Rev
Year: 2018
Identifier: PMID 29376219 DOI 10.1002/14651858.CD005195.pub4 · PMC6491296
Verification: verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
Retracted: no
Corrections: none Crossref update-to: new version of an earlier Cochrane review (not a retraction).
Extent checked: abstract only
Conflicts of interest and funding: COI statement in record: 1. MV: none known. 2. TF: none known. 3. CDG: none known. 4. GD: none known. 5. MZw: none known. 6. MB: none known. 7. MZe: Maurice Zeegers is the first investigator and the coauthor of included observational and experimental studies. 8. MH: none known. 9. RDA: none known. 10. CMC: none kn; funding listed: NCCIH NIH HHS

2. Research question

Does selenium prevent cancer, and what is the aetiological relation between selenium and cancer?

3. Study design and population

Study design: Meta-analysis – Cochrane systematic review of RCTs and observational studies
Population: Adults
Country: Multinational
Period: Search to February 2017
Sample size: 83 studies; 10 RCTs (27,232 participants); 70 cohorts (>2,360,000)
Inclusion and exclusion criteria: RCTs and longitudinal observational studies

4. Methods and endpoints

Exposure / intervention: Selenium supplements or exposure
Comparator: Placebo / low exposure
Endpoints: Cancer incidence and mortality; adverse effects incl. type 2 diabetes
Statistical methods: Random-effects meta-analysis; GRADE

5. Actual results

Results: Low-bias RCTs: any cancer RR 1.01 (0.93-1.10; high certainty); cancer mortality RR 1.02 (0.80-1.30); prostate RR 1.01 (0.90-1.14). SELECT: more alopecia and dermatitis and, with high baseline selenium, more high-grade prostate cancer. RCTs showed a slightly increased risk of type 2 diabetes with supplementation (numbers not given in abstract).
Absolute risks: not reported in abstract
Authors' conclusion: Well-conducted RCTs show no benefit of selenium for cancer prevention (high certainty); some RCTs raised concerns about high-grade prostate cancer and type 2 diabetes.

6. Strengths

Cochrane, GRADE
High-certainty null for cancer

7. Weaknesses

Diabetes outcome not quantified in abstract
Mostly male participants

8. Risk of bias

Orienting tool: AMSTAR 2
Type of assessment: simplified assessment (abstract only)
Full formal assessment: no
Overall risk of bias: low
Rationale: Cochrane methods.

9. Assessment of the statistical interpretation

Precise null for cancer.

10. Relevance to the specific claim

Confirms no cancer benefit of selenium (C-SUP-01) and a diabetes concern across RCTs (C-SUP-07).

11. Independent contrary findings

Observational inverse associations (confounded).

12. Transferability to Germany and Europe

Applicable.

13. Overall methodological judgement

High-certainty null for cancer; supportive of the diabetes signal.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	high
Risk of bias	low
Precision of results	high
Directness	direct
Reproducibility	replicated
Consistency with the overall evidence	consistent
Regional transferability	high
Adequacy of the interpretation (by the archive)	not applicable

14. Open questions

Size of the diabetes risk.