FNOA: Antioxidants (2011-2012)
The objective of this review was to assess the effects of antioxidant vitamin or mineral supplementation on the progression of age-related macular degeneration.
Randomized controlled trials comparing antioxidant vitamin or mineral supplementation (alone or in combination) to a placebo or no intervention in people with age-related macular degeneration in one or both eyes.
Excluded if not included above.
Recruitment
The following databases were searched: Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library (2007, Issue 3), MEDLINE (1966 to August 2007), EMBASE (1980 to August 2007), NRR (2007, Issue 3), AMED (1985 to January 2006), PubMed (24 January 2006 covering last 60 days) and SIGLE (1980 to March 2005).
Reference lists of identified reports were reviewed, as well as the Science Citation Index. Investigators and experts in the field were contacted for details of unpublished studies.
Design
Systematic review
Blinding used
Not applicable
Intervention
Author extracted data and assessed trial quality
Statistical Analysis
Data were pooled using a random-effects model unless three or fewer trials were available in which case a fixed-effects model was used.
Timing of Measurements
Not applicable
Dependent Variables
Age-related macular degeneration
Independent Variables
- Antioxidant vitamin or mineral supplementation (alone or in combination). Antioxidants were defined as any vitamin or mineral which is know to have antioxidant properties in vivo or which is known to be an important component of an antioxidant enzyme present in the retina, such as vitamin C, vitamin E, carotenoids, selenium and zinc.
- Control group (placebo or no intervention).
Control Variables
- Initial N: 577 reports originally identified
- Attrition (final N): Nine reports and eight trials included in the review
- Two large trials with reasonably long treatment duration and follow-up of four to six years
- Six smaller trials (ranging from 20-151 participants) with shorter duration and follow-up of six to 24 months
- Age: Average age of participants was 70 years
- Ethnicity: Not reported
- Other relevant demographics: Not reported
- Anthropometrics: Not reported
- Location: Largest study was from the United States.
Key Findings
- The majority of people were randomized in one trial (AREDS in the United States) that found a beneficial effect of antioxidant (beta-carotene, vitamin C and vitamin E) and zinc supplementation on progression to advanced age-related macular degeneration (adjusted odds ratio=0.68, 99% confidence interval: 0.49 to 0.93)
- People taking supplements were less likely to lose 15 or more letters of visual acuity (adjusted odds ratio=0.77, 99% confidence interval: 0.58 to 1.03)
- Hospitalization for genito-urinary problems was more common in people taking zinc and yellowing of the skin was more common in people taking antioxidants
- In general, the other trials were small and the result were inconsistent.
The evidence as to the effectiveness of antioxidant vitamin and mineral supplementation in halting the progression of age-related macular degeneration come mainly from one large trial in the United States. The generalizability of these findings to other populations with different nutritional status is not known. Further large, well-conducted randomized controlled trials in other populations are required. Long-term harm from supplementation cannot be ruled out. Beta-carotene has been found to increase the risk of lung cancer in smokers, and vitamin E has been associated with an increased risk of heart failure in people with vascular disease or diabetes.
Other: | Not reported |
Review includes only eight studies (nine reports).
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? | 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 | |