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FNOA: Antioxidants (2011-2012)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

The aim of this review was to examine the evidence as to whether or not taking vitamin or mineral supplements prevents the development of age-related macular degeneration.

Inclusion Criteria:
  • Randomized trials comparing an antioxidant vitamin or mineral supplement (alone or in combination) to control
  • Studies where supplementation had been given for at least one year
  • The following antioxidants were considered: Vitamin C, vitamin E, carotenoids, selenium and zinc
  • Participants in the trials were people in the general population with or without diseases other than age-related macular degeneration.
Exclusion Criteria:

Trials in which the participants were exclusively people with age-related macular degeneration.

Description of Study Protocol:

Recruitment

  • The following databases were searched:
    • Cochrane Central Register of Controlled Trials (CENTRAL), which contains the Cochrane Eyes and Vision Group Trials Register in the Cochrane Library (2007, Issue 3)
    • MEDLINE (1966 to August 2007)
    • SIGLE (1980 to 2005/03)
    • EMBASE (1980 to August 2007)
    • National Research Register (2007, Issue 3)
    • AMED (1985 to January 2006)
    • PubMed (on 24 January 2006 covering the last 60 days).
  • Reference lists of identified reports and the Science Citation Index were also reviewed
  • Investigators and experts in the field were contacted for details of unpublished studies. 

Design

Systematic review.

Intervention

Both review authors independently extracted data and assessed trial quality.

Statistical Analysis

  • Data were pooled using a fixed-effect model
  • Data were summarized using the risk ratio, after testing for heterogeneity between trial results using a standard chi-squared test
  • Sensitivity analyses were conducted to determine the impact of study quality on effect size.
Data Collection Summary:

Timing of Measurements

Duration of supplementation ranged from four to 12 years.

Dependent Variables

  • Number of participants developing age-related macular degeneration
  • Number of participants with visual loss due to age-related macular degeneration
  • Quality of life measures
  • Any adverse effects reported.

Independent Variables

  • The following antioxidants were considered: Vitamin C, vitamin E, carotenoids, selenium and zinc
  • Only vitamin E and beta-carotene were studied in the three trials.
Description of Actual Data Sample:
  • Initial N: Initial search resulted in 3,178 titles and abstracts
  • Attrition (final N): Three randomized trials included, representing 23,099 people. Two studies recruited men only and one study recruited men and women.
  • Age: Not reported
  • Ethnicity: Not reported
  • Other relevant demographics: Not reported
  • Anthropometrics: Not reported
  • Location: Australia, Finland and the United States.
Summary of Results:

Key Findings

  • All three trials were of high quality
  • Trials investigated alpha-tocopherol and beta-carotene supplements
  • There was no evidence that antioxidant vitamin supplementation prevented or delayed the onset of age-related macular degeneration
  • The pooled risk ratio for any age-related maculopathy was 1.04 (95% confidence interval, 0.92 to 1.18) and for age-related macular degeneration was 1.03 (95% confidence interval, 0.74 to 1.43)
  • Similar results were seen when the analyses were restricted to beta-carotene and alpha-tocopherol.
Author Conclusion:

There is no evidence to date that the general population should take antioxidant vitamin and mineral supplements to prevent or delay the onset of age-related macular degeneration. There are several large ongoing trials.

Funding Source:
Other: Not reported
Reviewer Comments:

Only three trials identified and they investigated vitamin E and beta-carotene only.

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? Yes
 
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