Iron Intake and Risk of Colorectal Cancer: A Systematic Review and Meta-Analysis Open Access
Dang, Kristina Van (2013)
Published
Abstract
Background. Despite moderate decreases in recent years due largely to improved screening and early detection of tumors, colorectal cancer is the third most common cancer in the world. Of the risk factors still associated with risk for colorectal cancer, diet is the only modifiable one. Only recently, epidemiological and experimental evidence suggests a role of iron intake and colorectal cancer incidence.
Objective. This systematic review and meta-analysis endeavors to estimate the role of iron intake--using the indicators serum ferritin, transferrin saturation, and heme iron--and risk of colorectal cancer.
Methods. A systematic review of articles using PubMed, Web of Science, Google Scholar, MedlinePlus, and Cochrane databases was conducted, and additional articles were identified through reference harvesting.
Results. 13 prospective studies were ultimately included in the quantitative analysis, spanning from 1966 to 2006. These analyses include a total cohort of 195,681 participants, and 5,806 incident cases of colorectal cancer. The summary odds ratio for ferritin was 0.90 (0.58-1.39), transferrin saturation was 0.94 (0.80-1.12), and heme iron was 1.13 (1.02-1.25). Only the quantitative analysis of ferritin yielded significant heterogeneity (x2=17.20; p=0.004; I2=71%). Publication bias was not present for any of the iron indicators.
Discussion. Much of the heterogeneity within the ferritin studies can be explained by the relatively short study period, contrasted with the induction period of colorectal cancer. Furthermore, the small number of studies in each separate analysis makes it difficult to draw definitive conclusions, and assigns a greater weight to each study.
Conclusion. The current literature does not support the hypothesis that iron intake is causally related to the risk for colorectal cancer, regardless of the methods used to assess exposure. This analysis did not find a significant association for serum ferritin and transferrin saturation, and a weak association for heme iron. Although the evidence supporting the positive relationship between meat consumption and colorectal cancer is convincing, we cannot conclude that the effect of meat is attributable to iron.
Table of Contents
Background........................................................................................................................ 1
Methods.............................................................................................................................. 5
Results................................................................................................................................ 7
Overview of study selection and exclusions........................................................................ 7
Qualitative review of included studies................................................................................ 8
Meta-analysis of ferritin studies....................................................................................... 13
Meta-analysis of transferrin saturation studies................................................................. 14
Meta-analysis of heme iron studies.................................................................................. 15
Discussion........................................................................................................................ 17
Summary of evidence...................................................................................................... 17
Strengths and Weaknesses............................................................................................ 19
Conclusion....................................................................................................................... 21
Summary........................................................................................................................ 21
Future Directions............................................................................................................ 21
References........................................................................................................................ 22
Tables & Figures............................................................................................................. 31
Figure 1. Flow diagram of study selection...................................................................... 31
Table 1. Summary characteristics of studies included in ferritin analysis......................... 32
Table 2. Summary characteristics of studies included in transferrin saturation analysis... 33
Table 3. Summary characteristics of studies included in heme iron analysis.................... 34
Table 4. Summary of study quality indicators................................................................. 35
Figure 2. Forest plot of studies included in ferritin analysis............................................. 36
Figure 3. Funnel plot of studies included in ferritin analysis........................................... 36
Figure 4. Forest plot of studies included in transferrin saturation analysis...................... 37
Figure 5. Funnel plot of studies included in transferrin saturation analysis..................... 37
Figure 6. Forest plot of studies included in heme iron analysis....................................... 38
Figure 7. Funnel plot of studies included in heme iron analysis...................................... 38
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