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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

Omega 3 and 6 oils for primary prevention of allergic disease: systematic review and meta-analysis

C Anandan, U Nurmatov, and A Sheikh.

Review published: 2009.

Link to full article: [Journal publisher]

CRD summary

This review evaluated the effectiveness of omega 3 and 6 oils for the primary prevention of sensitisation, eczema or atopic dermatitis, allergic rhinitis, asthma, and other allergic disorders. The authors concluded that supplementation did not lower the risk of sensitisation or allergic disease. This was a well-conducted review and the conclusion appears to be reliable for the population studied.

Authors' objectives

To evaluate the effectiveness of omega 3 and 6 oils in the primary prevention of sensitisation, eczema or atopic dermatitis, allergic rhinitis, asthma, and other allergic disorders.

Searching

Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, LILACS, PsycINFO, AMED, and Web of Science were searched and Google Scholar was used to search the Internet, with dates spanning from 1966 to 2008. The bibliographies of relevant studies were scanned for additional material. Unpublished and ongoing trials were sought from the meta Register of Controlled Trials, ClinicalTrials.gov, and the NRR. Manufacturers and field experts were also contacted for further studies. There were no language restrictions.

Study selection

Double-blind, placebo-controlled, randomised controlled trials (RCTs) of omega 3 and 6 oil supplements (used in isolation or in combination) were eligible for inclusion. The participants of interest were those at low or high risk of developing eczema or atopic dermatitis, allergic rhinitis, asthma, and other allergic disorders. Trials of people with an existing allergic condition were excluded.

All the included trials had high-risk individuals as part of the population. Participants were pregnant or breastfeeding women, or newborns (mainly formula-fed). Omega 3 supplements were contained within fish oils, and omega 6 supplements were contained within whey hydrolysate formula and borage oil, or borage oil alone. Treatment duration ranged from 20 weeks gestation to delivery up to the first six months after birth.

Two independent reviewers selected the studies for inclusion. Disagreements were resolved by discussion, or by arbitration with a third reviewer.

Assessment of study quality

Trial quality was assessed using the following Cochrane criteria: allocation concealment, method of treatment allocation, reporting of exclusions, completeness of follow-up, and reporting of complications. Each parameter was scored as A (low risk of bias), B (moderate risk of bias), or C (high risk of bias), and an overall assessment was recorded for each trial. The Jadad quality assessment tool was also used to assess allocation concealment, blinding, and withdrawals. Trials were scored from 0 (low quality) to 5 (high quality).

Two independent reviewers assessed the quality of the included trials.

Data extraction

Data were extracted to calculate relative risks (RRs) and 95% confidence intervals (CIs). This was carried out by one reviewer and checked by a second reviewer. Disagreements were resolved by discussion, or by arbitration with a third reviewer.

Methods of synthesis

RRs and 95% CIs were synthesised in a meta-analysis using a fixed-effect model, where heterogeneity (measured by the I2 statistic) was absent. A random-effects model was used where I2 was greater than 40%, or where there were only two trials available for the analysis. Where possible, publication bias was assessed using funnel plots, or using the Begg-Mazumdar and Egger tests. Sensitivity analysis was not performed, due to the small number of included trials.

Results of the review

Six RCTs were included in the review (n=938 participants). Four trials (n=679) compared omega 3, and two trials (n=259) compared omega 6, with placebo. A further eight on-going trials were found, the details of which were reported in the paper. Trial quality was scored A (Cochrane) and 5 (Jadad) in five trials; and B and 3 in one trial.

The meta-analysis showed that there were no statistically significant benefits in favour of omega 3 or 6 supplementation on any outcome relating to eczema or atopic dermatitis, asthma, allergic rhinitis, or food allergy. The results of other analyses were inconsistent in the development of sensitisation to common allergens, with only one trial reporting a statistically significant effect of omega 6 supplementation on lowering serum immunoglobulin E levels (p<0.01) in atopic participants. Omega 3 supplementation was associated with statistically significant benefits in immunological response, but the effects were either short term or inconsistent.

Authors' conclusions

Supplementation with omega 3, 6, or both was unlikely to prevent sensitisation or allergic disease.

CRD commentary

The review question was clear and this was supported by potentially reproducible inclusion criteria. The search strategy included some relevant sources, and there were clear efforts to minimise language and publication biases. The review process was conducted with sufficient attempts to minimise error and bias. An appropriate validity assessment was carried out, and the results of this indicated the high quality of the included trials. Other study details were reported adequately, including those for a number of on-going trials. Heterogeneity was assessed, and the chosen methods of synthesis appeared to be appropriate.

This was a well-conducted review and the authors' conclusions appear to be reliable for the population under investigation.

Implications of the review for practice and research

Research: The authors stated that future trials should build on the findings of this review, ensuring that mechanistic, clinical, and health service endpoints are considered.

Practice: The authors stated that omega 3 and 6 supplementation could not be recommended for the prevention of allergic disease.

Funding

Chief Scientist's Office (CZG/2/339).

Bibliographic details

Anandan C, Nurmatov U, Sheikh A. Omega 3 and 6 oils for primary prevention of allergic disease: systematic review and meta-analysis. Allergy 2009; 64(6): 840-848. [PubMed: 19392990]

Indexing Status

Subject indexing assigned by NLM

MeSH

Animals; Asthma /epidemiology /prevention & control; Dermatitis, Atopic /epidemiology /prevention & control; Dietary Supplements; Eczema /epidemiology /prevention & control; Fatty Acids, Omega-3 /administration & dosage; Fatty Acids, Omega-6 /administration & dosage; Food Hypersensitivity /epidemiology /prevention & control; Humans; Hypersensitivity /epidemiology /prevention & control; Rhinitis, Allergic, Seasonal /epidemiology /prevention & control

AccessionNumber

12009105889

Database entry date

17/03/2010

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 19392990

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