EAL

DLM: Vitamin E, C, B-carotene Supplements and All-Cause Mortality (2007-2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To conduct a meta-analysis of randomized controlled trials (RCTs) to evaluate the role of vitamin E in the prevention of cancer in adults.

Inclusion Criteria:

RCTs in which outcomes related to cancer prevention were associated with the intake of vitamin E supplement alone or with other supplements vs. a control group (placebo or control)
Adult population (over age 18 years) men and women subjects
Supplements were in capsule or tablet form consumed orally.

The primary outcomes were:

Total mortality
Cancer mortality
Total incidence of cancer or specific incidence of lung, stomach, esophageal, prostate, breast, urinary, hematological or thyroid cancers.

Secondary outcomes were: Role of high dose (greater than 300mg per day) and low dose (less than 300mg) vitamin E on the primary outcome.

Exclusion Criteria:

If a study lacked sufficient methodological research quality, it was discussed and possibly excluded per reviewer agreement
A Jadad score was determined in the decision-making process.

Description of Study Protocol:

Recruitment: Research articles were gleaned from The Cochrane Controlled Trials Register (CCTR), MEDLINE and EMBASE. Search terms included: Antioxidants, vitamins, vitamin E, alpha-tocopherol, tocopherol, cancer, prevention and randomized controlled trials.
Design: Two RCTs were reviewed
Statistical analysis: The Cochrane Statistics package, RevMan, version 4.2, was used for data synthesis. Relative risk and risk difference with 95% confidence intervals were reported. Heterogeneity was tested using the Cochran Q statistic with significance at P<0.1.

Data Collection Summary:

Timing of Measurements

510 days to 10 years duration.

Dependent Variables

Total mortality
Cancer mortality
Total incidence of cancer
Specific incidence of cancer for lung, stomach, esophageal, pancreatic, prostate, breast or thyroid cancers.

Independent Variable

Vitamin E dose (50mg to 800mg per day).

Description of Actual Data Sample:

Total N: 167,025 adults in 12 trials; more than 76,000 or 45% were females. The remainder were male subjects.
Age: 18 years of age and older
Ethnicity: Patients were from Finland, Italy, Canada, China, the United Kingdom, the United States of America, Denmark, Germany, Ireland, the Netherlands, Norway, Spain, Sweden, Switzerland and Mexico.
Location: Europe, China, Mexico and various western countries.

Summary of Results:

Findings

For vitamin E alone or with other supplements vs. control, the vitamin E was associated with a significant reduction in the incidence of prostate cancer, but the vitamin E supplements did not reduce the incidence of any other type of cancer
Vitamin E was associated with a significant reduction in the incidence of prostate cancer (relative risk, 0.85; 95% CI, 0.73 to 0.96; number needed to treat, 500)
There were no statistically significant differences in total mortality (relative risk, 0.99; 95% CI, 0.96 to 1.03), cancer incidence (odds ratio, 10.96; 95% CI, 0.92 to 1.01) and cancer mortality (odds ratio, 1.00; 95% CI, 0.96 to 1.03), among the different groups of patients included in this meta-analysis.

Author Conclusion:

Vitamin E supplementation was not associated with a reduction in total mortality, cancer incidence or cancer mortality, but it was associated with a statistically significant reduction in the incidence of prostate cancer
Vitamin E supplementation can be used for the prevention of prostate cancer among high-risk groups, including men older than 55 years of age, patients with elevated prostate specific antigen (PSA), African-Americans and patients with family history of prostate cancer.

Funding Source:

University/Hospital:

Dept of Family Medicine and Polyclinic, Riyadh, Saudi Arabia

Reviewer Comments:

Quality Criteria Checklist: Review Articles
Relevance Questions
	1.	Will the answer if true, have a direct bearing on the health of patients?	Yes
	2.	Is the outcome or topic something that patients/clients/population groups would care about?	Yes
	3.	Is the problem addressed in the review one that is relevant to dietetics practice?	Yes
	4.	Will the information, if true, require a change in practice?	???

Validity Questions
	1.	Was the question for the review clearly focused and appropriate?	Yes
	2.	Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described?	Yes
	3.	Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased?	Yes
	4.	Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible?	Yes
	5.	Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined?	Yes
	6.	Was the outcome of interest clearly indicated? Were other potential harms and benefits considered?	Yes
	7.	Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described?	Yes
	8.	Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included?	Yes
	9.	Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed?	Yes
	10.	Was bias due to the review's funding or sponsorship unlikely?	Yes