Elsevier

Clinical Nutrition

Volume 33, Issue 1, February 2014, Pages 59-63
Clinical Nutrition

Meta-analyses
Dietary flavonoids intake and risk of type 2 diabetes: A meta-analysis of prospective cohort studies

https://doi.org/10.1016/j.clnu.2013.03.011Get rights and content

Summary

Background & aims

Flavonoids may have cardioprotective effects, but epidemiological evidence on the relationship of dietary flavonoids with diabetes has not been systematically assessed. To examine the association between dietary flavonoids and type 2 diabetes, we performed a meta-analysis on this topic.

Methods

We searched PubMed through March 2013 for relevant cohort studies that assessed total flavonoids and type 2 diabetes risks. A fixed-effect model was used to calculate the summary risk estimates.

Results

Four articles consisting of 6 prospective cohorts that involved 18,146 cases and 284,806 participants were identified. The summary relative risk (RR) of type 2 diabetes for the highest intake of total flavonoids compared with the lowest was 0.91 (95% confidence interval (CI): 0.87–0.96). Furthermore, an increase in the total flavonoids intake of 500 mg/d was associated with a significant risk reduction of 5% (RR = 0.95, 95% CI: 0.91–0.98). In subgroup analyses, the observed beneficial effects were observed in US population, in those mean age > 40 years old people and in studies ≥20 years in duration.

Conclusions

The present meta-analysis indicates that consumption of dietary total flavonoids is associated with a reduced risk of type 2 diabetes.

Introduction

The increasing prevalence of diabetes in the world has become a serious public health challenge of the 21st century.1 Primary prevention of diabetes is therefore of considerable public health priority. Fruit and vegetables are important modifiable risk factors for type 2 diabetes. Although some dietary factors have been found to reduce the risk of type 2 diabetes, the relation between the intake of fruit and vegetables and the incidence of type 2 diabetes remains unclear. Hamer reviewed 5 prospective cohort studies, and concluded that there was no significant association between consumption of fruit and vegetables and a substantial reduction in the risk of type 2 diabetes.2 In an updated meta-analysis, Carter summarized 6 cohort studies. Although no significant benefits were observed for increasing intake of vegetables, fruit, or fruit and vegetables combined on incidence of type 2 diabetes, they found that increasing daily intake of green leaf vegetables could significantly reduce the risk of type 2 diabetes.3 Thus, the mechanism for the observed beneficial effects of dietary factors on type 2 diabetes remains need to be clarified.

Flavonoids represent a group of naturally occurring polyphenoic compounds present in various fruits and vegetables. Flavonoids are effective antioxidants, thus they may exert cardioprotective effects in human populations.4 However, to our knowledge, epidemiological evidence on the relationship of dietary flavonoids with diabetes has not been systematically assessed. We therefore conducted a systematical review and meta-analysis of prospective cohort studies to explore the effects of dietary flavonoids intake on incidence of type 2 diabetes, and to examine whether a dose–response effect exists between flavonoids intake and type 2 diabetes.

Section snippets

Search strategy

We conducted a systematic literature search of PubMed database through March 2013 by using the following search terms: “flavonoids”, “catechin”, “flavanones”, “flavones”, “anthocyanidins”, and “type 2 diabetes”, “prediabetes”, “impaired glucose tolerance”, “impaired fasting glucose”. Besides, we carried out a manual search using reference lists of retrieved articles original and recent reviews. However, we did not retrieve the conference literature, gray literature and unpublished literature.

Study selection

To

Literature search

Fig 1 displays the study selection process. The search strategy yielded a total of 365 articles. After a review of the titles and abstracts, 354 articles did not meet our inclusion criteria and therefore could not be included. Of the 11 articles remained, 7 articles were excluded for the reasons listed in the Fig. 1,10, 11, 12, 13, 14, 15, 19 thus leaving 4 articles for the meta-analysis.16, 17, 18, 20

Study characteristics

The characteristics of the included studies are shown in Table 1. Among the 4 articles, Wedick

Discussions

The results of this meta-analysis of prospective cohort studies suggest that high intakes of flavonoids were inversely associated with the risk of type 2 diabetes. The dose–response analysis indicates that for 500 mg/d consumption of flavonoids, the RR of type 2 diabetes was 0.95 (0.91–0.98).

Flavonoids are the largest plant polyphenolics regularly ingested by humans. The present study based on observational data demonstrates an anti-diabetic effect of dietary flavonoids intake. Ideally, a

Conclusions

This meta-analysis demonstrates that higher consumption of total dietary flavonoids, in a dose-dependent manner, is associated with a significantly decreased risk of type 2 diabetes. However, given the relative paucity of data, further optimally designed research in other ethnic groups is warranted before recommending total flavonoids intake as a public health strategy to reduce risks of type 2 diabetes.

Statement of authorship

HQQ designed research; LYJ and HQQ searched the literature and extracted data. LYJ, ZJ, LXL, WY, and JJ analyzed the data, HQQ and LYJ wrote the paper. HQQ had primary responsibility for final content. All authors read and approved the final manuscript.

Conflict of interest

There are no conflicts of interest to disclose.

Acknowledgements

None declared.

References (29)

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