FNOA: Antioxidants (2011-2012)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To assess the effect of antioxidant supplements (beta carotene, vitamin A, vitamin C and vitamin E, and selenium) on overall mortality in primary or secondary prevention randomized clinical trials.
Inclusion Criteria:
The present review is based on studies that took place in Europe, North and South America, Asia and Australia.
Inclusion details:
- Adults ranging in age from 18 to 103 years
- Cancer and mortality were the main outcome measures
- Antioxidants, administered alone or in combination with minerals or other interventions
- Healthy participants were in the primary prevention trials
- Unhealthy participants with a disease were included in the secondary prevention trials.
Exclusion Criteria:
- Less than 18 years of age
- Children or pregnant women
- Tertiary prevention trials
- Studies that violated the purpose or outcome of the mortality study.
Description of Study Protocol:
- Recruitment: All primary and secondary prevention randomized clinical trials on antioxidant supplements (beta carotene, vitamin A, vitamin C and vitamin E, and selenium) vs. placebo or no intervention
- Design: Three authors extracted data. Trials with adequate randomization, blinding and follow-up were classified as having a low risk of bias. Disagreement was resolved by discussion or in consultation with the article authors. Trial authors were contacted if there was missing information.
- Blinding used: Yes
- Interventions: Antioxidant supplements (beta carotene, vitamins A, C and E, and selenium) vs. placebo or no intervention
- Statistical analysis: Random effects and fixed effects meta analysis were performed. Random effects meta regression analysis were performed to assess sources of intertrial heterogeneity.
Data Collection Summary:
Timing of Measurements
The dates used for search in various data banks were 1945 to 2006.
Dependent Variable
Mortality data in healthy participants and patients with various diseases.
Independent Variables
- Antioxidant supplements (beta carotene, vitamins A, C and E, and selenium) vs. placebo or no intervention
- Antioxidant supplements were administered orally and included doses of 1.2mg to 50mg (mean, 18mg) beta-carotene, 1,333 IU to 200,000 IU (mean, 20,219 IU) vitamin A, 60mg to 2,000mg (mean, 497mg) vitamin C, 10 IU to 5,000 IU (mean, 70 IU) vitamin E and 20mcg to 200mcg (mean, 99mcg) selenium daily or on alternate days for durations lasting 28 days to 12 years.
- Mean duration of follow-up in all trials was 3.4 years.
Description of Actual Data Sample:
- Number of articles identified: 16,111
- Number of studies reviewed: 386
- Number included: 67 RCTs
- Sample size in studies: Between 24 and 39,876 participants
- Age: 18 to 103 years; average age was 60 years or older
- Ethnicity: Chinese, US citizens and European citizens
- Location: China, US, Switzerland and Germany.
Summary of Results:
Findings
- There was no effect on mortality in a random-effects meta-analysis (RR, 1.02; 95% CI, 0.99 to 1.06). However, in a fixed-effect meta-analysis, antioxidant supplements significantly increased mortality (RR, 1.04; 95% CI, 1.02 to 1.06).
- Antioxidants significantly increased mortality (RR, 1.05; 95% CI, 1.02 to 1.08) in trials with low risk of bias. Antioxidants were assessed separately.
- The fat-soluble supplements significantly increased mortality. RR and 95% CI were as follows
- Vitamin A: RR, 1.16; 95% CI, 1.10 to 1.24)
- Beta-carotene: RR, 1.07; 95% CI, 1.02 to 1.11)
- Vitamin E: RR, 1.04; 95% CI, 1.01 to 1.07)
- There was no significant effect for vitamin C (RR, 1.06; 95% CI, 0.94 to 1.20) or selenium (RR, 0.90; 95% CI, 0.80 to 1.01).
Author Conclusion:
- No evidence was found to support antioxidant supplements for primary or secondary prevention
- Vitamin A, beta carotene and vitamin E may increase mortality
- Antioxidants supplements should be considered medicinal products and should undergo more evaluation before marketing occurs.
Funding Source:
University/Hospital: | Copenhagen University Hospital |
Other: |
Reviewer Comments:
Quality Criteria Checklist: Review Articles
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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? | No | |
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 | |