EAL

FNOA: Antioxidants (2011-2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The objective of this review was to assess the effects of antioxidant vitamin or mineral supplementation on the progression of age-related macular degeneration.

Inclusion Criteria:

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.

Exclusion Criteria:

Excluded if not included above.

Description of Study Protocol:

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 Investigators and experts in the field were contacted for details of unpublished studies.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.

Data Collection Summary:

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

Description of Actual Data Sample:

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.

Summary of Results:

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.

Author Conclusion:

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.

Funding Source:

Other:

Not reported

Reviewer Comments:

Review includes only eight studies (nine reports).

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