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Meta-Analysis
. 2012;7(7):e41641.
doi: 10.1371/journal.pone.0041641. Epub 2012 Jul 26.

Body iron stores and heme-iron intake in relation to risk of type 2 diabetes: a systematic review and meta-analysis

Zhuoxian Zhao  1 , Sheyu Li, Guanjian Liu, Fangfang Yan, Xuelei Ma, Zeyu Huang, Haoming Tian
Affiliations
Meta-Analysis

Body iron stores and heme-iron intake in relation to risk of type 2 diabetes: a systematic review and meta-analysis

Zhuoxian Zhao et al. PLoS One. 2012.

Abstract

Background and objective: Emerging evidence from biological and epidemiological studies has suggested that body iron stores and heme-iron intake may be related to the risk of type 2 diabetes (T2D). We aimed to examine the association of body iron stores and heme-iron intake with T2D risk by conducting a systematic review and meta-analysis of previously published studies.

Research design and methods: Systematic review and subsequent meta-analysis were conducted by searching MEDLINE database up to June 22, 2012 to identify studies that analyzed the association of body iron stores or dietary heme-iron intake with T2D risk. The meta-analysis was performed using the effect estimates and 95% confidence intervals (CIs) to calculate the pooled risk estimates, while the heterogeneity among studies was examined using the I(2) and Q statistic.

Results: The meta-analysis included 16 high-quality studies: 12 studies analyzed ferritin levels (4,366 T2D patients and 41,091 controls) and 4 measured heme-iron intake (9,246 T2D patients and 179,689 controls). The combined relative risk (RR) comparing the highest and lowest category of ferritin levels was 1.66 (95% CI: 1.15-2.39) for prospective studies, 2.29 (95% CI: 1.48-3.54) for cross-sectional studies with heterogeneity (Q = 14.84, p = 0.01, I(2) = 66.3%; Q = 44.16, p<0.001, I(2) = 88.7%). The combined RR comparing the highest and lowest category of heme-iron intake was 1.31 (95% CI: 1.21-1.43) with heterogeneity (Q = 1.39, p = 0.71, I(2) = 0%). No publication bias was found. Additional 15 studies that were of good quality, had significant results, and analyzed the association between body iron stores and T2D risk were qualitatively included in the systematic review.

Conclusions: The meta-analysis and systematic review suggest that increased ferritin levels and heme-iron intake are both associated with higher risk of T2D.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Selection of studies for meta-analysis.
Figure 2
Figure 2. Forest plot showing the effect estimates of each prospective study and the pooled relative risk comparing the highest with the lowest category of ferritin levels.
*dotted line represented the combined effect estimate of meta-analysis. Size of square and rhomboids represented weight.
Figure 3
Figure 3. Forest plot showing the effect estimates of each cross-sectional study and the pooled relative risk comparing the highest with the lowest category of ferritin levels.
*dotted line represented the combined effect estimate of meta-analysis. Size of square and rhomboids represented weight.
Figure 4
Figure 4. Forest plot showing the effect estimates of each cohort study and the pooled relative risk comparing the highest with the lowest category of heme-iron intake levels.
*dotted line represented the combined effect estimate of meta-analysis. Size of square and rhomboids represented weight.
Figure 5
Figure 5. Begg’s Funnel Plots for visual assessment of the presence of publication bias for 6 prospective studies of ferritin in the meta-analysis.
Begg’s bias (P = 0.851).
Figure 6
Figure 6. Egger’s Funnel Plots for visual assessment of the presence of publication bias for 6 prospective studies of ferritin in the meta-analysis.
Egger’s bias (P = 0.772).
Figure 7
Figure 7. Begg’s Funnel Plot for visual assessment of the presence of publication bias for 6 cross-sectional studies of ferritin in the meta-analysis.
Begg’s bias (P = 0.188).
Figure 8
Figure 8. Egger’s Funnel Plot for visual assessment of the presence of publication bias for 6 cross-sectional studies of ferritin in the meta-analysis.
Egger’s bias (P = 0.124).
Figure 9
Figure 9. Begg’s and Funnel Plot for visual assessment of the presence of publication bias for 4 cohort studies of heme-iron intake in the meta-analysis.
Begg’s bias (P = 0.497).
Figure 10
Figure 10. Egger’s Funnel Plot for visual assessment of the presence of publication bias for 4 cohort studies of heme-iron intake in the meta-analysis.
Egger’s bias (P = 0.658).
Figure 11
Figure 11. Galbraith plot of the ferritin levels for the association with type 2 diabetes for prospective studies.
The regression runs through the origin interval (central solid line). Between the two outer parallel lines is the 95% confidence interval.
Figure 12
Figure 12. Galbraith plot of the ferritin levels for the association with type 2 diabetes for cross-sectional studies.
The regression runs through the origin interval (central solid line). Between the two outer parallel lines is the 95% confidence interval.
See this image and copyright information in PMC

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