Folate-related nutrients, genetic polymorphisms, and colorectal cancer risk: the fukuoka colorectal cancer study

MTHFR Gene C677T Polymorphism (rs1801133) and Susceptibility to Colorectal Polyps in an Azerbaijani Population

BACKGROUND

Understanding the relationships between the methylenetetrahydrofolate reductase (MTHFR) gene polymorphism, colorectal polyps, and CRC risk can aid in advancing personalized medicine approaches in CRC prevention. The aim of the current study is to identify the association of C677T polymorphism of the MTHFR gene with the risk of colorectal polyps in the Azerbaijani population.

METHODS

This study included 125 patients with colon polyps and 155 healthy individuals as a control group. DNA was extracted from venous blood samples obtained from patients and healthy individuals, and the results were analyzed through polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and agarose gel electrophoresis.

RESULTS

Wild-type, heterozygote, and homozygous mutant were revealed within 69 (55.2%), 49 (39.2%), and 7 (5.6%) patients and within 100 (64.5%), 45 (29%), and 10 (6.5%) healthy controls, respectively. However, no significant statistical associations were observed between CT and TT genotypes, dominant (CC vs. CT + TT) and recessive (CC + CT vs. TT) models, and the mutant T allele and disease risk. There were also no significant differences between patients and controls regarding age, sex, smoking and alcohol use.

CONCLUSION

Our research did not reveal any significant association between the MTHFR C677T polymorphism and susceptibility to colorectal polyps in the Azerbaijan population.

Association between nutrient intake related to the one-carbon metabolism and colorectal cancer risk: a case-control study in the Basque Country

PURPOSE

Epidemiologic evidence for the association between methyl-donor nutrient intake and colorectal cancer (CRC) risk remains inconclusive. We aimed to examine the relationship between intake of vitamins of the B group, methionine, total choline and betaine and CRC risk, in a population from the CRC screening programme in the Basque Country.

DESIGN

This observational study included 308 patients with CRC and 308 age- and sex-matched subjects as controls. During recruitment, dietary, anthropometric, lifestyle, socioeconomic, demographic, and health status information was collected. Conditional logistic regression was used to estimate the odds ratios (ORs) for CRC risk.

RESULTS

The adjusted ORs for CRC risk decreased with higher intakes of choline and betaine (p < 0.05). After further adjustment for folate, high intake of choline and betaine remained associated with a reduced CRC risk (adjusted model for choline, OR third tertile vs first tertile = 0.45, 95% CI 0.26-0.80, p = 0.006; for betaine, OR third tertile vs first tertile = 0.27, 95% CI 0.16-0.47, p < 0.001). Regarding the other nutrients, our findings indicated a non-significant decrease in CRC risk with the high level of intake.

CONCLUSIONS

Our data suggest that choline and betaine intake influence CRC risk in the studied population.

High serum riboflavin is associated with the risk of sporadic colorectal cancer

BACKGROUND

Experimental results indicate that riboflavin is involved in tumorigenesis. Data regarding the relationship between riboflavin and colorectal cancer (CRC) are limited, and findings vary between observational studies.

DESIGN

This was a case-control retrospective study.

OBJECTIVE

This study aimed to evaluate the associations between serum riboflavin level and sporadic CRC risk.

METHODS

In total, 389 participants were enrolled in this study - including 83 CRC patients without family history and 306 healthy controls - between January 2020 and March 2021 at the Department of Colorectal Surgery and Endoscope Center at Xinhua Hospital, Shanghai Jiao Tong University School of Medicine. Age, sex, body mass index, history of polyps, disease conditions (e.g., diabetes), medications, and eight other vitamins were used as confounding factors. Adjusted smoothing spline plots, subgroup analysis, and multivariate logistic regression analysis were conducted to estimate the relative risk between serum riboflavin levels and sporadic CRC risk. After fully adjusting for the confounding factors, an increased risk of colorectal cancer was suggested for individuals with higher levels of serum riboflavin (OR = 1.08 (1.01, 1.15), p = 0.03) in a dose-response relationship.

CONCLUSIONS

Our results support the hypothesis that higher levels of riboflavin may play a role in facilitating colorectal carcinogenesis. The finding of high levels of circulating riboflavin in patients with CRC warrants further investigation.

Dietary B vitamin and methionine intakes and risk for colorectal cancer: a case-control study in China

B vitamins (including folate, vitamin B2, vitamin B6 and vitamin B12) and methionine are essential for methylation reactions, nucleotide synthesis, DNA stability and DNA repair. However, epidemiological evidence among Chinese populations is limited. The objective of this study was to evaluate B vitamins and methionine in relation to colorectal cancer risk in a Chinese population. A case-control study was conducted from July 2010 to April 2019. A total of 2502 patients with colorectal cancer were recruited along with 2538 age- (5-year interval) and sex-matched controls. Dietary data were collected using a validated FFQ. Multivariable logistic regression was used to assess OR and 95 % CI. The intake of folate, vitamin B2, vitamin B6 and vitamin B12 was inversely associated with colorectal cancer risk. The multivariable OR for the highest quartile v. the lowest quartile were 0·62 (95 % CI 0·51, 0·74; Ptrend < 0·001) for folate, 0·46 (95 % CI 0·38, 0·55; Ptrend < 0·001) for vitamin B2, 0·55 (95 % CI 0·46, 0·76; Ptrend < 0·001) for vitamin B6 and 0·72 (95 % CI 0·60, 0·86; Ptrend < 0·001) for vitamin B12. No statistically significant association was found between methionine intake and colorectal cancer risk. Stratified analysis by sex showed that the inverse associations between vitamin B12 and methionine intake and colorectal cancer risk were found only among women. This study indicated that higher intake of folate, vitamin B2, vitamin B6 and vitamin B12 was associated with decreased risk of colorectal cancer in a Chinese population.

Meta-analysis of homocysteine-related factors on the risk of colorectal cancer

The major objective of this meta-analysis was to examine the association between homocysteine and related measurements with the risk of colorectal cancer (CRC) and adenomatous polyps (AP). Many studies presented an association between methyltetrahydrofolate reductase (MTHFR) gene polymorphisms and risk of CRC. Yet, there have been variances on what homocysteine-related and dietary factors play on the risk of CRC or AP, in association with folate-related one carbon metabolism pathways. We pooled analyses to examine comprehensively all homocysteine related factors including blood tests measurements, dietary, and lifestyle factors for their associations with the risk of CRC and AP. We located 86 articles published from 1995 to 2017. The results revealed that elevated homocysteine levels and decreased vitamin B12 levels in the blood were associated with increased risks of CRC and AP, with case-control studies having greater significant effect sizes compared to that of cohort-control studies. Decreased methionine and vitamin B6 levels in the blood increased the risk of CRC. MTHFR 677 TT and CT polymorphisms were interacting with elevated homocysteine levels to increase the risk of CRC. Decreased dietary fiber, methionine, vitamin B9 or folate, and vitamin B6 intakes were associated with increased risks of CRC; whereas, increased dietary B12 intake, alcohol intake, and smoking were associated with increased risk of CRC. Further studies can be conducted to examine the mechanistic differences of blood levels of homocysteine-related and dietary factors, including different types of dietary fiber, for their effects on decreasing the homocysteine toxicity to prevent CRC.

Vitamin B2 intake reduces the risk for colorectal cancer: a dose-response analysis

PURPOSE

Several epidemiological studies have assessed the ability of vitamin B₂ to prevent colorectal cancer (CRC), but the results are controversial results. We conducted a dose-response meta-analysis to investigate the association between vitamin B₂ and CRC risk.

METHODS

We searched the PubMed and EMBASE database until January 3, 2018 to identify relevant studies. The pooled relative risks (RRs) with the corresponding 95% confidence intervals (CIs) were calculated using a random-effects model or fixed-effects model. The dose-response relationship was assessed by restricted cubic splines.

RESULTS

A total of 14 studies reporting vitamin B₂ intake and two studies reporting blood vitamin B₂ concentration, comprising 14,934 cases and 1593 cases, respectively, were included in the meta-analysis. Vitamin B₂ intake was inversely associated with CRC risk (RR = 0.87; 95% CI 0.81-0.93). Similar results were found for total vitamin B₂ intake from diet and supplements (RR = 0.86; 95% CI 0.78-0.94) and dietary vitamin B₂ intake (RR = 0.89, 95% CI 0.82-0.98) in subgroup analyses. The dose-response model indicated a non-linear trend, and CRC risk was reduced by 10% when vitamin B₂ intake increased to 5 mg/day. In addition, high blood concentrations of vitamin B₂ could also reduce the CRC risk (RR = 0.74; 95% CI 0.59-0.92).

CONCLUSIONS

This dose-response analysis indicates that vitamin B₂ intake is inversely associated with CRC risk. The inverse association may also exist between blood vitamin B₂ concentration and CRC risk. These results suggest the importance of vitamin B₂ intake in the prevention of CRC.

MTRR rs1801394 and its interaction with MTHFR rs1801133 in colorectal cancer: a case-control study and meta-analysis

AIM

This study aims to evaluate the association between the MTRR rs1801394 alone or in interaction with the MTHFR rs1801133 and susceptibility to colorectal cancer (CRC) and its characteristics in Iranian population. Additionally, both a systematic review and meta-analysis were performed to derive a more precise assessment of this association.

MATERIALS & METHODS

Genomic DNA of 2332 subjects was genotyped for rs1801394. These data were pooled with 17 eligible studies for meta-analysis.

RESULTS

No significant association was found between the rs1801394 or rs1801394-rs1801133 and CRC risk. Meta-analysis results also demonstrated no significant relationship between the rs1801394 and CRC risk.

CONCLUSION

Results of this study showed that the rs1801394 alone or together with the rs1801133 is not a risk factor for CRC in Iranian population.

Vitamin B2 intake and colorectal cancer risk; results from the Nurses' Health Study and the Health Professionals Follow-Up Study cohort

Vitamin B2 serves as a cofactor to enhance one-carbon metabolism, maintain mucous membranes, and has been implicated in lowering colorectal cancer (CRC) risk. However, few prospective studies have examined the association between vitamin B2 intake and CRC. In this study, we estimated the associations between vitamin B2 intake and CRC risk using the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS) cohorts. Vitamin B2 intake was measured by a validated food frequency questionnaire every 4 years. Among 100,033 women in the NHS and 44,007 men in the HPFS we documented a total of 3,037 incident CRC cases (2,093 women and 944 men) during 24-26 years of follow-up until 2010. Intakes of total (from food and supplements), dietary (from food only), and supplemental vitamin B2 were inversely related to CRC risk in age-adjusted analysis in NHS. However, the association was attenuated and no longer statistically significant in multivariate analysis (p-trend ≥0.08). The pooled multivariate relative risks (95% confidence interval) comparing individuals in the extreme quintiles of intakes were 0.93 (0.81-1.06) for total vitamin B2, 0.89 (0.61-1.28) for dietary vitamin B2 and 0.94 (0.81-1.08) for supplemental vitamin B2. These associations of total vitamin B2 intake were similar for risk of CRC with varying lag-time periods (0-4, 4-8, 8-12 or 12-16 years), for risk of CRC subtypes by tumor location, and across strata of intake of folate or alcohol. Our prospective data do not support a beneficial role of vitamin B2 intake in lowering incidence of CRC.

TSER polymorphism is not associated with risk of pediatric acute lymphoblastic leukemia: A meta-analysis

BACKGROUND

Accumulating studies have explored the effect of thymidylate synthase enhancer region (TSER) variation on risk of pediatric acute lymphoblastic leukemia (ALL) with controversial results. Therefore, this quantitative meta-analysis was performed to assess synthetically the association of TSER variation with susceptibility to develop pediatric ALL.

METHODS

The PubMed, ScienceDirect, Google Scholar, Wanfang Database, and China National Knowledge Infrastructure were systematically retrieved to obtain the published case-control studies about the relationship between TSER variation and pediatric ALL risk. The quality assessment of the included studies was preformed and relevant information was collected. Odds ratios (ORs) and 95% confidence intervals (CIs) were applied to evaluate the strength of association.

RESULTS

This meta-analysis finally included 2681 children with ALL and 3854 matched controls from 11 investigations. The quantitative synthesis results found no significant association between TSER variation and susceptibility to pediatric ALL in overall comparisons under 5 genetic models (2R/3R vs 3R/3R: OR = 0.95, 95% CI = 0.84-1.07, P = 0.41; 2R/2R vs 3R/3R: OR = 0.99, 95% CI = 0.84-1.16, P = 0.90; 2R2R vs 3R/3R+2R/3R: OR = 1.05, 95% CI = 0.92-1.21, P = 0.45; 2R/3R+2R/2R vs 3R/3R: OR = 0.97, 95% CI = 0.87-1.09, P = 0.63; 2R vs 3R: OR = 1.03, 95% CI = 0.92-1.15, P = 0.61). Similarly, there was no significant association existed in the stratification analyses according to ethnicity, control source, and quality score.

CONCLUSION

This meta-analysis shows that TSER variation is not related to the development risk of pediatric ALL.

Association of MTRR A66G polymorphism with cancer susceptibility: Evidence from 85 studies

Methionine synthase reductase (MTRR) is a key regulatory enzyme involved in the folate metabolic pathway. Previous studies investigating the association of MTRR A66G polymorphism with cancer susceptibility reported inconclusive results. We performed the current meta-analysis to obtain a more precise estimation of the possible association. Published literatures were identified from PubMed, Embase and CBM databases up to October 2016. The strength of the association between the MTRR A66G polymorphism and cancer susceptibility was assessed using odds ratios (ORs) and the corresponding 95% confidence intervals (CIs). Eighty five published studies with 32,272 cases and 37,427 controls were included in this meta-analysis. Pooled results indicated that the MTRR A66G polymorphism was associated with an increased overall cancer risk (homozygous model: OR = 1.08, 95% CI = 1.02-1.15, P = 0.009; recessive model: OR = 1.06, 95% CI = 1.00-1.12, P < 0.001 and allele comparison: OR = 1.03, 95% CI = 1.00-1.06, P < 0.001). Stratification analysis further indicated significant associations in head and neck cancer, Caucasians, Africans, and high quality studies. However, to avoid the "false-positive report", the significant findings were assessed by the false-positive report probability (FPRP) test. Interestingly, the results of FPRP test revealed that the increased risk for MTRR A66G polymorphism among Africans need further validation due to the high probabilities of false-positive results. This meta-analysis suggests that the MTRR A66G polymorphism is associated with significantly increased cancer risk, a finding that needs to be confirmed in single large studies.

Thymidylate Synthase Polymorphisms and Risk of Lung Cancer among the Jordanian Population: a Case Control Study

BACKGROUND

Thymidylate synthase (TS) catalyzes the methylation of deoxyuridylate to deoxythymidylate and is involved in DNA methylation, synthesis and repair. Two common polymorphisms have been reported, tandem repeats in the promoter-enhancer region (TSER), and 6bp ins/del in the 5'UTR, that are implicated in a number of human diseases, including cancer. The association between the two polymorphisms in risk for lung cancer (LC) was here investigated in the Jordanian population.

MATERIALS AND METHODS

An age, gender, and smoking-matched case-control study involving 84 lung cancer cases and 71 controls was conducted. The polymerase chain reaction/restriction fragment length polymorphism (PCR-RFLP) technique was used to detect the polymorphism of interest.

RESULTS

Individuals bearing the ins/ins genotype were 2.5 times more likely to have lung cancer [(95%CI: 0.98-6.37), p=0.051]. Individuals who were less than or equal to 57 years and carrying ins/ins genotype were 4.6 times more susceptible to lung cancer [OR<57 vs >57years: 4.6 (95%CI: 0.93-22.5), p=0.059)]. Genotypes and alleles of TSER were distributed similarly between cases and controls. Weak linkage disequilibrium existed between the two loci of interest (Lewontin's coefficient [D']) (LC: D' =0.03, r2: 0. 001, p= 0.8;

CONTROLS

D' =0.29, r2: 0.08, p=0.02). Carriers of the "3 tandem repeats_insertion" haplotype (3R_ins) were 2 times more likely to have lung cancer [2 (95%CI: 1.13-3.48), p=0.061].

CONCLUSIONS

Genetic polymorphism of TS at 3` UTR and its haplotype analysis may modulate the risk of lung cancer in Jordanians. The 6bp ins/del polymorphism of TS at 3 `UTR is more informative than TSER polymorphism in predicting increased risk.

ASSOCIATION OF MTHFR A1298C POLYMORPHISM WITH BREAST CANCER AND/OR OVARIAN CANCER RISK: AN UPDATED META-ANALYSIS

BACKGROUND

Recent years have witnessed the discovery of similar gene variations between breast cancer and ovarian cancer, inherited breast and ovarian cancer in particular. A large number of case-control studies have been conducted to explore the association of Methylenetetrahydrofolate Reductase (MTHFR) A1298C polymorphism with breast cancer and/or ovarian cancer risk. However, the results are still inconsistent and inconclusive. Consequently, we performed a meta-analysis to evaluate the association between MTHFR A1298C polymorphism and breast, ovarian cancer risk.

MATERIALS AND METHODS

A comprehensive retrieval was conducted in the electronic database of PubMed, Web of Science and Chinese National Knowledge Infrastructure (CNKI) until June 2015 to identify eligible studies. A total of 35 studies which examined the association of MTHFR A1298C polymorphism with breast cancer and/or ovarian cancer were identified. The pooled odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the effect of gene polymorphism. And allele model, homozygous model, co-dominant model, dominant model, recessive model were applied.

RESULT

In the overall analysis, significantly increased breast cancer and/or ovarian cancer risk was found (for allele model A VS C OR = 1.05, CI: 1.02-1.08, P = 4χ10-3; for homozygous model AA VS CC OR = 1.11, CI: 1.03-1.19, P = 5χ10-3; for recessive model (AC +AA) VS CC: OR = 1.10, CI: 1.03-1.18, P = 7χ10-3).

CONCLUSION

In the subgroup analysis, significantly increased breast cancer risk was identified among Caucasians. MTHFR A1298C polymorphism might contribute to an increased risk of breast cancer and/or ovarian cancer susceptibility. In addition, MTHFR A1298C polymorphism had a significant association with breast cancer in Caucasians.

Associations between vitamin D receptor (VDR) gene polymorphisms and colorectal cancer risk and effect modifications of dietary calcium and vitamin D in a Japanese population

Much interest has been drawn to possible associations between vitamin D receptor (VDR) gene polymorphisms and colorectal cancer risk in conjunction with potentially protective effects of calcium and vitamin D. In a study of 685 cases of colorectal cancer and 778 community controls in Japan, we examined the associations of the FokI, BsmI, ApaI, and TaqI polymorphisms with colorectal cancer risk and effect modification by dietary calcium and vitamin D. Genotypes were determined by the PCR-RFLP method. The ApaI polymorphism seemed to be associated with a decreased risk of colorectal cancer, particularly of rectal cancer. The adjusted odds ratio of colorectal cancer for the ApaI AA and Aa genotypes combined versus the aa genotype was 0.83 (95% confidence interval [CI] 0.67-1.02), and the corresponding value for rectal cancer was 0.75 (95%CI 0.56-0.99). A decreased risk of colorectal cancer for the ApaI AA and Aa genotypes combined was more evident in individuals with high calcium intake (interaction p=0.055). The FokI polymorphism seemed to be associated with a decreased risk of colon cancer among those with high vitamin D intake (interaction p=0.09). The BsmI and TaqI polymorphisms were unrelated to colorectal cancer risk, and the null associations were not modified by calcium or vitamin D intake. In conclusion, the ApaI polymorphism may be associated with a decreased risk of colorectal cancer in Japanese, dependent on dietary calcium intake.

Associations of the A66G Methionine Synthase Reductase Polymorphism in Colorectal Cancer: A Systematic Review and Meta-Analysis

Inconsistency in the reported associations between the A66G polymorphism in the methionine synthase reductase (MTRR) gene and colorectal cancer (CRC) prompted a meta-analysis, so that we could obtain a more precise estimate. Databases searches of the published literature yielded 20 case–control studies from 17 articles (8,371 cases and 12,574 controls). We calculated pooled odds ratios (ORs) and 95% confidence intervals in three genetic comparisons (A allele, G allele, and A/G genotype). We found no evidence of overall associations between MTRR A66G and CRC risk (OR 0.96–1.05, P = 0.12–0.44). This was materially unchanged when reanalyzed without the Hardy–Weinberg equilibrium (HWE)-deviating studies (OR 0.97–1.06, P = 0.11–0.65). In the A allele comparison, however, outlier treatment generated significant protection (OR 0.91, P = 0.01). Combined removal of the outliers and HWE-deviating studies reflected this summary effect (OR 0.90, P = 0.01) as did the pooled OR from high-quality studies (OR 0.90, P = 0.01). Only the Asian subgroup showed significant (both at P = 0.05) A allele (OR 1.13) and A/G genotype (OR 0.88) associations. In conclusion, post-outlier A allele effects were protective. Our study also suggests ethnic-specific associations with Asian susceptibility and protection in the A allele and A/G genotype comparisons, respectively. Folate status showed no association of this polymorphism with CRC.

A dose-response meta-analysis reveals an association between vitamin B12 and colorectal cancer risk

OBJECTIVE

The current meta-analysis evaluated the association between vitamin B12 intake and blood vitamin B12 level and colorectal cancer (CRC) risk.

DESIGN

The PubMed and EMBASE databases were searched. A dose-response analysis was performed with generalized least squares regression, with the relative risk (RR) and 95 % CI as effect values.

SETTING

The meta-analysis included seventeen studies.

SUBJECTS

A total of 10 601 patients.

RESULTS

The non-linear dose-response relationship between total vitamin B12 intake and CRC risk was insignificant (P=0·690), but the relationship between dietary vitamin B12 intake and CRC risk was significant (P<0·001). Every 4·5 μg/d increment in total and dietary vitamin B12 intake was inversely associated with CRC risk (total intake: RR=0·963; 95 % CI 0·928, 0·999; dietary intake: RR=0·914; 95 % CI 0·856, 0·977). The inverse association between vitamin B12 intake and CRC risk was also significant when vitamin B12 intake was over a dosage threshold, enhancing the non-linear relationship. The non-linear dose-response relationship between blood vitamin B12 level and CRC risk was insignificant (P=0·219). There was an insignificant association between every 150 pmol/l increment in blood vitamin B12 level and CRC risk (RR=1·023; 95 % CI 0·881, 1·187).

CONCLUSIONS

Our meta-analysis indicates that evidence supports the use of vitamin B12 for cancer prevention, especially among populations with high-dose vitamin B12 intake, and that the association between CRC risk and total vitamin B12 intake is stronger than between CRC risk and dietary vitamin B12 intake only.

Proteomic Analysis of One-carbon Metabolism-related Marker in Liver of Rat Offspring

Maternal food intake has a significant effect on the fetal environment, and an inadequate maternal diet may result in intrauterine growth restriction. Intrauterine growth restriction newborn rat pups nursed by normal diet-fed dams exhibited rapid catch-up growth, which plays a critical role in the risk for metabolic and cardiovascular disease in later life. Specifically, one-carbon metabolism in the liver plays a critical role in placental and fetal growth. Impaired functioning of one-carbon metabolism is associated with increased homocysteine levels. In this study, we applied a comprehensive proteomic approach to identify differential expression of proteins related to one-carbon metabolism in the livers of rat offspring as an effect of maternal food restriction during gestation. Data are available via ProteomeXchange with identifier PXD002578. We determined that betaine-homocysteine S-methyltransferase 1, methylenetetrahydrofolate dehydrogenase 1, and ATP synthase subunit beta mitochondrial (ATP5B) expression levels were significantly reduced in the livers of rat offspring exposed to maternal food restriction during gestation compared with in the offspring of rats fed a normal diet (p < 0.05). Moreover, the expression levels of betaine-homocysteine S-methyltransferase 1, methylenetetrahydrofolate dehydrogenase 1, and ATP synthase subunit beta mitochondrial were negatively correlated with serum homocysteine concentration in male offspring exposed to maternal food restriction during gestation and normal diet during lactation. However, in female offspring only expression levels of methylenetetrahydrofolate dehydrogenase 1 were negatively correlated with homocysteine concentration. This study shows that maternal food restriction during late gestation and normal diet during lactation lead to increased homocysteine concentration through disturbance of one-carbon metabolism in the livers of male offspring. This suggests that male offspring have an increased gender-specific susceptibility to disease in later life through fetal programming.

Gene-diet interactions and their impact on colorectal cancer risk

A number of studies have evaluated the role of gene-diet interaction in the etiology of colorectal cancer (CRC). Historically, these studies focused on established dietary risk factors and genes involved in their metabolism. However, results from these candidate gene studies were inconsistent, possibly due to multiple testing and publication bias. In recent years, genome-wide association studies have identified a number of CRC susceptibility loci, and subsequent meta-analyses have observed limited evidence that diet may modify the risk associated with these susceptibility loci. Statistical techniques have been recently developed to evaluate the presence of interaction across the entire genome; results from these genome-wide studies have demonstrated limited evidence of interaction and have failed to replicate results from candidate gene studies and those using established susceptibility loci. However, larger sample sizes are likely needed to elucidate modest or weak interaction in genome-wide studies of gene-diet interaction.