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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].

Dietary fiber intake and risk of first stroke: a systematic review and meta-analysis

DE Threapleton, DC Greenwood, CE Evans, CL Cleghorn, C Nykjaer, C Woodhead, JE Cade, CP Gale, and VJ Burley.

Review published: 2013.

Link to full article: [Journal publisher]

CRD summary

This review concluded that higher total dietary fibre intake was significantly associated with lower risk of first stroke. Potential for missed studies, publication bias and significant heterogeneity mean the authors' conclusion may not be reliable.

Authors' objectives

To assess whether total dietary fibre intake or fibre from key food sources is associated with risk of primary stroke events.

Searching

MEDLINE, MEDLINE in-process, EMBASE, CAB Abstracts, Web of Science, BIOSIS and The Cochrane Library were searched for studies published in English between January 1990 and November 2009; search terms were reported. The search was updated to May 2012 using the databases MEDLINE, MEDLINE in-process and EMBASE. Reference lists of relevant articles and selected journals were handsearched.

Study selection

Prospective observational studies with a minimum follow-up of three years that reported incident first stroke events in relation to dietary fibre intake in generally healthy participants were eligible for inclusion.

The included studies were conducted in the United States, Japan, northern Europe and Australia. Age at recruitment ranged between 25 and 79 years and average age ranged from 49 to 65 years, where reported. Most studies included both men and women. Most studies reported stroke incidence data; two studies only reported fatal stroke events and one only reported ischaemic stroke incidence. Fibre intake was estimated using Association of Official Analytical Chemist fibre values (or equivalent) in most studies.

Full paper screening was undertaken independently by two reviewers. Disagreements were resolved by a third reviewer.

Assessment of study quality

The authors did not use a formal quality assessment tool. Aspects of study quality (such as study design, follow-up duration, case ascertainment and adjustment for various important confounders) were assessed during data extraction.

Data extraction

Relative risk data with 95% confidence intervals were extracted from the studies. Because the included studies used different definitions for their exposure categories, a dose-response trend was estimated for each study, using the method recommended by Greenland and Longnecker.

The authors did not state how many reviewers performed data extraction.

Methods of synthesis

The estimated dose-response trends were pooled using a random-effects model. Nonlinear dose-response curves were combined using multivariate meta-analysis. Heterogeneity was assessed using the Cochran Q statistic and quantified using I². Pooled results were presented only where Ι² was less than 75% and where studies included appropriate adjustments. Meta-regression of predefined study characteristics was undertaken, including aspects of study quality. Publication bias was assessed using funnel plots and Egger's test of asymmetry.

Results of the review

Eight cohort studies with a total of 11,236 cases (case numbers ranged from 95 fatal strokes to 2,781 incident events) were included in the review. Study follow-up ranged from eight to 19 years.

Total fibre intake was associated with a statistically significant reduction in stroke risk (RR per 7g/day increase 0.93, 95% CI 0.88 to 0.98; seven studies); there was evidence of heterogeneity for this result (I²=59%). Risk steadily reduced with increasing total fibre intake. There was evidence of publication bias. Estimates were generally unchanged when subgroups were pooled using meta-regression.

There was no statistically significant association between soluble fibre intake and stroke risk (RR per 4g/day increase 0.94, 95% CI 0.88 to 1.01; three studies).

There was significant heterogeneity in the meta-analysis of cereal fibre intake and stroke risk (I²=90%) so the pooled results were not reported and individual study results were presented.

Individual study results were presented for ischaemic stroke risk, haemorrhagic stroke risk, the association between insoluble fibre and stroke risk and the association between fruit and vegetable fibre and stroke risk.

Authors' conclusions

Higher total dietary fibre intake was significantly associated with lower risk of first stroke.

CRD commentary

The review question and inclusion criteria were clear. There was a comprehensive search but language restrictions were applied so relevant studies may have been missed. Selection of full papers was undertaken independently by two reviewers to reduce potential for reviewer bias and error; it was unclear whether data extraction was performed in a similar manner. Some aspects of study quality were abstracted from the included studies and these study characteristics were used in meta-regression.

Pooling appeared generally appropriate. The authors did not report pooled results when heterogeneity was very high. There was evidence of statistical heterogeneity and publication bias for the main result. The authors acknowledged that some of the differences in results seen in the two European studies may have been because of differences in population characteristics and main sources of fibre within the diet when compared with the United States or Japan.

Owing to the potential for missed studies, publication bias and significant heterogeneity, the authors' conclusion may not be reliable.

Implications of the review for practice and research

Practice: The authors stated that their review supported guidelines to increase fibre consumption.

Research: The authors stated that further research should be undertaken to explore the association between risk of stroke (assessing different stroke types) and different sources of fibre (such as cereal, fruit and vegetable sources) and also soluble/insoluble fibre. They stated that the identification of potentially protective food sources of fibre may help tailor recommendations for at-risk populations.

Funding

Department of Health, England. The main author's PhD studentship was sponsored by Kellogg Marketing and Sales Company (UK) Ltd.

Bibliographic details

Threapleton DE, Greenwood DC, Evans CE, Cleghorn CL, Nykjaer C, Woodhead C, Cade JE, Gale CP, Burley VJ. Dietary fiber intake and risk of first stroke: a systematic review and meta-analysis. Stroke 2013; 44(5): 1360-1368. [PubMed: 23539529]

Indexing Status

Subject indexing assigned by NLM

MeSH

Dietary Fiber; Fruit; Humans; Incidence; Risk; Stroke /epidemiology /etiology; Vegetables

AccessionNumber

12013028493

Database entry date

17/09/2013

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: 23539529

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