Dietary Carbohydrate and Prostate Cancer Risk: A Meta-Analysis

Carbohydrate intake has been inconsistently associated with risk of prostate cancer. We review and quantitatively summarize the evidence from observational studies in a meta-analysis. We searched the PubMed database for observational studies related to the association of carbohydrate intake and prostate cancer risk up to December 25, 2013. Summary relative risks (RRs) were estimated by the use of a random effects model. We included 13 case-control studies with 4,367 cases and 6,205 controls, and 5 cohort studies with 3,679 cases and 74,115 participants in this meta-analysis. The summary RR of prostate cancer for the highest vs. the lowest carbohydrate intake was 1.06 [95% confidence interval (CI): 0.93–1.20, I² = 46.8%] for all included studies. In the subgroup analyses stratified by study design, the summary RRs for the highest vs. the lowest carbohydrate intake were 1.04 (95% CI: 0.87–1.23) for case-control studies and 1.06 (95% CI: 0.88–1.28) for cohort studies. For the 5 studies that reported results for advanced prostate cancer, the summary RR was 0.92 (95% CI: 0.71–1.20). This meta-analysis of observational studies indicates that there is no association between carbohydrate intake and prostate cancer risk. Further studies are needed to confirm our findings.     

Coffee Drinking and the Risk of Endometrial Cancer: An Updated Meta-Analysis of Observational Studies

Background: Several compounds contained in coffee have been found to suppress carcinogenesis in experimental studies. We conducted a dose–response meta-analysis to assess the impact of coffee consumption on the risk of endometrial cancer. Materials and methods: We searched MEDLINE and EMBASE databases for studies published up to August 2016. Using random effects models, we estimated summary relative risks (RR) for cohort studies and odds ratios (OR) for case-control studies with 95% confidence intervals (CI). Dose–response analyses were conducted by using generalized least square trend estimation. Results: We identified 12 cohort studies and 8 case-control studies eligible for inclusion, contributing with 11,663 and 2,746 endometrial cancer cases, respectively. The summary RR for highest compared with lowest coffee intake was 0.74 (95% CI: 0.68–0.81; p_{heterogeneity} = 0.09, I² = 32%). The corresponding summary RR among cohort studies was 0.78 (95% CI: 0.71–0.85; p_{heterogeneity} = 0.14, I² = 31.9%) and 0.63 (95% CI: 0.53–0.76; p_{heterogeneity} = 0.57, I² = 0%) for case-control studies. One-cup increment per day was associated with 3% risk reduction (95% CI: 2–4%) in cohort studies and 12% (95% CI: 5–18%) in case-control studies. After pooling the results from 5 cohort studies, the association remained significant only in women with body mass index over 30 (RR = 0.71, 95% CI: 0.61–0.81). Conclusion: The results from our meta-analysis strengthen the evidence of a protective effect of coffee consumption on the risk of EC and further suggest that increased coffee intake might be particularly beneficial for women with obesity.     

Citrus fruit intake and bladder cancer risk: a meta-analysis of observational studies

Epidemiological studies have investigated the association between citrus fruit and bladder cancer risk; however, the results are inconsistent. To assess these issues, we conducted a meta-analysis of currently available studies. We identified relevant articles by searching the MEDLINE and EMBASE databases. We calculated the summary relative risk (RR) with 95% confidence interval (95% CI) using a random effect model. We included eight case–control studies and six cohort studies in the meta-analysis. There was a significant inverse association between citrus fruit intake and bladder cancer risk in all pooled studies (RR: 0.85; 95% CI, 0.76–0.94) and case–control studies (RR: 0.77; 95% CI, 0.64–0.92), but not in the cohort studies (RR: 0.96; 95% CI, 0.87–1.07). Our results suggest that citrus fruit intake is related to decreased bladder cancer risk. Subsequent well-designed, large prospective studies are needed to obtain better understanding of this relationship.     

Dairy Consumption and Gastric Cancer Risk: A Meta-Analysis of Epidemiological Studies

Studies investigating the association of dairy consumption with gastric cancer risk have reported inconsistent findings. We conducted this systematic review and meta-analysis to review and summarize the epidemiologic evidence on the relation of total dairy and milk consumption with risk of gastric cancer. We summarized the available literature on this topic using meta-analysis of relative risks (RR) associated with total dairy and milk intake. The total of 17 case-control and 6 cohort studies (3256 cases) were eligible for inclusion. When comparing the highest with the lowest category of total dairy intake, the results of cohort studies indicated that increased consumption of total dairy food was associated with a reduced risk of gastric cancer (RR = 0.76; 95% CI: 0.64–0.91), whereas case-control studies provided no association. In subgroup analysis, significantly inverse associations between total diary food consumption and gastric cancer risk were observed in Europe subgroup (RR = 0.73; 95% CI: 0.54–0.99), U.S. subgroup (RR = 0.78; 95% CI: 0.63–0.98) but not in Asia subgroup. However, milk consumption was not associated with gastric cancer risk no matter in main or subgroup analysis. The results of cohort studies, but not case-control studies, suggested that total dairy might be related to the reduction of gastric cancer risk. Milk consumption was not associated with gastric cancer risk.     

Green Tea and Incidence of Colorectal Cancer: Evidence from Prospective Cohort Studies

A systematic meta-analysis of prospective cohort studies on green tea consumption and colorectal cancer was performed to determine whether green tea has a chemopreventive effect against colorectal cancer. Six eligible cohort studies involving 352,275 participants and 1675 cases of colorectal cancer were identified. Combined relative risk (RR) ratios for the highest vs. lowest and increment of 1 cup/day green tea consumption levels were calculated. The combined RR of 0.90 (95% CI: 0.72–1.08) was found comparing highest vs. lowest green tea consumption levels for colorectal cancer. No significant differences by cancer-site were found, but an inverse association between green tea and incidence of colorectal cancer (RR: 0.70; 95% CI: 0.55–0.85) and colon cancer (RR: 0.69; 95% CI: 0.48–0.98) was demonstrated in Shanghai population. Singapore men had a higher risk of colorectal cancer (RR: 1.36; 95% CI: 1.06–1.74). Furthermore, an increase in green tea consumption of 1 cup/day was not associated with incidence of colorectal cancer (RR: 0.97; 95% CI: 0.91–1.03). Despite the limited evidence from Shanghai studies in support of green tea as potential chemopreventive agents against colorectal cancer, available data from prospective cohort studies are insufficient to conclude that green tea may protect against colorectal cancer.     

Citrus fruits intake and prostate cancer risk: a quantitative systematic review

OBJECTIVES: The purpose of this systematic review was to investigate the association between dietary intake of citrus fruits and prostate cancer risk. METHODS: Authors searched electronic databases and the reference lists of publications of diet and prostate cancer studies until August 2007. All of the epidemiological studies that obtained individual data on dietary intake of citrus fruits and presented risk estimates of the association between intake of citrus fruits and risk of prostate cancer were identified and included. Using general variance-based methods, study-specific odds ratios (OR)/ relative risk (RR) and associated confidence interval (CI)/ standard error (SE) for highest versus lowest intake of citrus fruits level were extracted from each paper. RESULTS: Eleven articles including six case-control studies, one nested case-control study and four cohort studies, proved eligible. Overall summary OR using random effect model did not show an association in risk of prostate cancer with intake of citrus fruits (summary OR=1.03, 95% CI=0.89-1.19) with large heterogeneity across studies that we were unable to explain (I(2)=67.88%). The summary ORs in case-control studies and cohort studies were 1.10 (95% CI=0.97-1.22) and 1.05 (95% CI=0.96-1.14), respectively. CONCLUSIONS: Pooled results from observational studies did not show an association between intake of citrus fruits and the risk of prostate cancer, although results vary substantially across studies.     

Dietary calcium intake and risk of type 2 diabetes: possible confounding by magnesium

This study examined the association of dietary calcium intake with incident type 2 diabetes by a meta-analysis and explored the potential confounding by magnesium. Potential studies were identified by searching the PubMed database in September 2011. Prospective cohort studies that reported relative risks (RR) with 95% confidence intervals (CI) of type 2 diabetes for dietary calcium intake were selected. Results were combined using either a fixed- or random-effects model. Six prospective cohort studies comprising 264268 participants and 11225 reported cases were included. All combined random-effects meta-analysis yielded a significant pooled RR of 0.85 (95% CI 0.75-0.97). However, a sensitivity analysis limited to four studies with control for magnesium yielded an attenuated, nonsignificant pooled RR of 0.94 (95% CI 0.85-1.05). In conclusion, dietary calcium intake was not independently associated with risk of type 2 diabetes. The inverse association in prior observational studies may be partially confounded by magnesium intake.     

Lycopene Consumption and Risk of Colorectal Cancer: A Meta-Analysis of Observational Studies

A number of epidemiological studies have explored the association between lycopene or lycopene-rich food intake and the risk of colorectal cancer, but the results of these studies have not been consistent. We conducted a systematic review and meta-analysis of studies published in the PubMed and EMBASE databases to quantitatively assess the association between lycopene consumption and the risk of colorectal cancer. A total of 15 studies were included in the meta-analysis, and the summary relative risk (RR) for highest versus lowest category indicated no significant association between lycopene consumption and the risk of colorectal cancer [RR = 0.94, 95% confidence interval (CI): 0.80–1.10]. However, a significant inverse association was observed between lycopene consumption and the site of cancer in the colon (RR = 0.88, 95% CI: 0.81–0.96). We also found that the incidence of colon cancer and lycopene intake did not exhibit dose-response relationships. The Grades of Recommendations Assessment, Development and Evaluation (GRADE) quality in our study was very low. In conclusion, this meta-analysis indicates that lycopene consumption is not associated with the risk of colorectal cancer. Further research will be needed in this area to provide conclusive evidence.     

Glycemic index, glycemic load, and cancer risk: a meta-analysis

BACKGROUND: Factors linked to glucose metabolism play an important role in the development of cancers, and both glycemic index (GI) and glycemic load (GL) have been investigated as potential etiologic factors. OBJECTIVE: A meta-analysis was performed to explore the association between GI and GL and cancer risk from published studies. DESIGN: A comprehensive, systematic bibliographic search of the medical literature was conducted to identify relevant studies. Case-control and cohort studies published before October 2007 that reported cancer risk estimates for GI and GL were included. Pooled relative risks (RRs) were estimated for breast, colorectal, endometrial, and pancreatic cancer. RESULTS: Thirty-nine studies were included in the meta-analysis. The interquantile ranges of GL were significantly wider in case-control studies, most of which were conducted in European countries, than in cohort studies. Cohort studies that presented lower ranges of GL also reported lower risk estimates. Overall, both GL and GI were significantly associated with a greater risk of colorectal (summary RR = 1.26; 95% CI: 1.11, 1.44 and RR = 1.18; 95% CI: 1.05, 1.34, respectively) and endometrial (RR = 1.36; 95% CI: 1.14, 1.62 and RR = 1.22; 95% CI: 1.01, 1.49) cancer than of breast and pancreatic cancer. There was, however, a significant between-study heterogeneity for colorectal cancer (P < 0.0001). The association between GL and breast cancer disappeared when publication bias was taken into account. No association was found for pancreatic cancer. CONCLUSION: This comprehensive meta-analysis of GI and GL and cancer risk suggested an overall direct association with colorectal and endometrial cancer.     

Dietary Fat Intake and the Risk of Skin Cancer: A Systematic Review and Meta-Analysis of Observational Studies

Abstract

We conducted a meta-analysis to evaluate the association between fat intake and the risk of three major types of skin cancer including basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and cutaneous malignant melanoma (CMM). A comprehensive search of PubMed and EMBASE was performed to identify all relevant observational studies published up to December 1, 2018. Specific odds ratio (OR) or relative risk (RR) estimates for the highest versus the lowest intake of dietary fat and 95% confidence intervals (CI) from the included studies were pooled using random effect model. Three prospective cohort studies (175,675 participants and 30,915 BCC cases, 4,106 SCC cases and 1,638 CMM cases) and nine case-control studies (328 BCC cases, 493 SCC cases, 1,547 CMM cases and 2,660 controls) were identified. The pooled results indicated that dietary consumption of total fat and saturated fat were not associated with three major types of skin cancer. High consumption of monounsaturated fat was significantly associated with a decreased risk of BCC (RR: 0.90, 95% CI: 0.85–0.96) and high level of polyunsaturated fat intake was potentially positively associated with SCC (RR: 1.19, 95% CI: 1.06–1.33). Our findings should be confirmed by further evidence from well-designed and large-scale prospective cohort studies.     

Dietary fibre and risk of colorectal cancer in the Breast Cancer Detection Demonstration Project (BCDDP) follow-up cohort

BACKGROUND: The hypothesis that increased intake of dietary fibre lowers the risk of colorectal cancer (CRC) has recently been weakened by results from cohort and intervention studies that did not detect such an association. We investigated the association between dietary fibre intake and risk of CRC in a cohort of women that prospectively answered a food frequency questionnaire (FFQ). METHODS: We studied 45 491 women in the Breast Cancer Detection Demonstration Project (BCDDP) follow-up cohort. A 62-item FFQ was administered from 1987 and 1989 to assess dietary intake. Participants received follow-up questionnaires (in 1992-1995 and 1995-1998) on which they reported incident cancers. Cases were also identified through searches of the National Death Index and state cancer registries. Cox proportional hazard regression was used to generate risk ratios and 95% CI for quintiles of total fibre intake and fibre subtypes. RESULTS: During a mean follow-up time of 8.5 years we identified 487 colorectal cancer cases. The 10th and 90th percentiles of dietary fibre intake were 5.4 g and 18.2 g respectively. For total fibre we observed no association with colorectal cancer (fifth versus first quintile, RR = 0.94, 95% CI: 0.71-1.23). Analyses by subgroup of fibre and by anatomical subsite did not reveal any stronger inverse associations. CONCLUSIONS: Within a cohort of older women characterized by a relatively low fibre intake, there was little evidence that dietary fibre intake lowers the risk of colorectal cancer.     

Coffee Consumption and Prostate Cancer Risk: A Meta-Analysis of Cohort Studies

This meta-analysis was conducted to assess the association between coffee consumption and prostate cancer risk. Thirteen cohort studies with 34,105 cases and 539,577 participants were included in the meta-analysis. The summary relative risks (RRs) with 95% confidence intervals (CIs) for different coffee intake levels were calculated. Dose-response relationship was assessed using generalized least square trend estimation. The pooled RR for the highest vs. lowest coffee intake was 0.90 (95% CI: 0.85–0.95), with no significant heterogeneity across studies (P = 0.267; I²= 17.5%). The dose-response analysis showed a lower cancer risk decreased by 2.5% (RR = 0.975; 95% CI: 0.957–0.995) for every 2 cups/day increment in coffee consumption. Stratifying by geographic region, there was a statistically significant protective influence of coffee on prostate cancer risk among European populations. In subgroup analysis of prostate cancer grade, the summary RRs were 0.89 (95% CI: 0.83–0.96) for nonadvanced, 0.82 (95% CI: 0.61–1.10) for advanced and 0.76 (95% CI: 0.55–1.06) for fatal diseases. Our findings suggest that coffee consumption may be associated with a reduced risk of prostate cancer and it also has an inverse association with nonadvanced prostate cancer. Because of the limited number of studies, more prospective studies with large sample size are needed to confirm this association.     

Vitamin B6 Intake and the Risk of Colorectal Cancer: A Meta-Analysis of Prospective Cohort Studies

Objectives: We performed this meta-analysis to estimate the association between vitamin B₆ intake and colorectal cancer risk. Methods: Prospective cohort studies on vitamin B₆ intake and colorectal cancer risk were identified by searching databases from the period of 1960 to 2016. Results from individual studies were synthetically combined using Stata 13.0 software. Results: A total of 10 prospective cohort studies including 13 data sets were included in our meta-analysis, containing 7,817 cases and 784,550 subjects. The combined relative risks (RR) of colorectal cancer for the highest vitamin B₆ intake compared with the lowest vitamin B₆ intake was 0.88 [95% confidence intervals (CIs): 0.77–1.02]. Dose-response meta-analysis based on five eligible studies showed that for each additional 3 and 5 mg of vitamin B₆ intake, the risk would decrease by 11% (RR: 0.89, 95%CI: 0.81–0.98) and 17% (RR: 0.83, 95%CI: 0.71–0.97), respectively. Little evidence of publication bias was found. Conclusion: This meta-analysis provides evidence of a nonsignificant decrease in colorectal cancer risk associated with the high level of vitamin B₆ intake, but the risk in dose-response analysis is significant. However, the latter finding is based on a limited number of studies, which should be interpreted with caution.     

Dietary fiber and whole-grain consumption in relation to colorectal cancer in the NIH-AARP Diet and Health Study

BACKGROUND: Whether the intake of dietary fiber can protect against colorectal cancer is a long-standing question of considerable public health import, but the epidemiologic evidence has been inconsistent. OBJECTIVE: The objective was to investigate the relation between dietary fiber and whole-grain food intakes and invasive colorectal cancer in the prospective National Institutes of Health-AARP Diet and Health Study. DESIGN: The analytic cohort consisted of 291 988 men and 197 623 women aged 50-71 y. Diet was assessed with a self-administered food-frequency questionnaire at baseline in 1995-1996; 2974 incident colorectal cancer cases were identified during 5 y of follow-up. The Cox proportional hazards model was used to estimate the relative risks (RRs) and 95% CIs. RESULTS: Total dietary fiber intake was not associated with colorectal cancer. The multivariate RR for the highest compared with the lowest intake quintile (RR(Q5-Q1)) was 0.99 (95% CI: 0.85, 1.15; P for trend = 0.96). In analyses of fiber from different food sources, only fiber from grains was associated with a lower risk of colorectal cancer (multivariate RR(Q5-Q1): 0.86; 95% CI: 0.76, 0.98; P for trend = 0.01). Whole-grain intake was inversely associated with colorectal cancer risk: the multivariate RR(Q5-Q1) was 0.79 (95% CI: 0.70, 0.89) for the whole cohort (P for trend < 0.001). The association with whole grain was stronger for rectal than for colon cancer. CONCLUSIONS: In this large prospective cohort study, total dietary fiber intake was not associated with colorectal cancer risk, whereas whole-grain consumption was associated with a modest reduced risk.     

Flavonol intake and stroke risk: A meta-analysis of cohort studies

ObjectiveEpidemiologic findings are inconsistent regarding the association between flavonol intake and the risk for stroke. The aim of this study was to determine whether an association exists between them in observational studies.MethodsWe searched the PubMed and EMBASE databases for studies conducted from 1966 to August 2013. Prospective cohort studies that provided relative risk (RR) estimates with 95% confidence intervals (CIs) for the association between flavonol intake and risk for stroke were included. A random effects model was used to combine study-specific risk estimates.ResultsThe meta-analysis included eight studies, with 5228 stroke cases among 280 174 participants. The summary RR indicated a significant association between highest flavonol intake and reduced risk for stroke (summary RR, 0.86; 95% CI, 0.75–0.99). Furthermore, an increase in flavonol intake of 20 mg/d was associated with a 14% decrease in the risk for developing stroke (summary RR, 0.86; 95% CI, 0.77–0.96). Subgroup analyses suggested a significant inverse association between highest flavonol intake and stroke risk among men (summary RR, 0.74; 95% CI, 0.56–0.97) but not women (summary RR, 0.99; 95% CI, 0.85–1.16).ConclusionsHigher dietary flavonol intake is associated with a reduced risk for stroke, especially among men. Our results support recommendations for higher consumption of flavonol-rich foods to prevent stroke.     

Alcohol Consumption and Risk of Glioma: A Meta-Analysis of 19 Observational Studies

The relationship between risk of glioma and alcohol consumption has been widely studied, but results have been conflicting. We therefore conducted a meta-analysis of observational studies to systematically assess the relationship between alcohol drinking and risk of glioma. Two electronic databases (PubMed and EMBASE) were searched from inception to 8 August 2013 to identify pertinent studies that linked alcohol drinking with glioma risk. We used a random-effects model to calculate the overall relative risk (RR) with corresponding 95% confidence intervals (CIs). Fifteen case-control and four cohort studies were identified for this analysis. The combined RR for total alcohol drinkers versus non-drinkers was 0.96 (95% CI: 0.89–1.04). In the subgroup analysis by geographic area, a significant association was observed in North American studies (RR = 0.78, 95% CI: 0.65–0.93), but not in European or Asian/Australian studies. In the subgroup analysis by study design, a borderline significant association emerged in population-based case-control studies (RR = 0.82, 95% CI: 0.68–0.99), but not in hospital-based case-control studies (RR = 1.00, 95% CI: 0.99–1.01) or cohort group (RR = 1.03, 95% CI: 0.88–1.20). Our results show no material association between alcohol consumption and risk of glioma existed. Further prospective evidences are needed to confirm this association.     

Milk Consumption and Bladder Cancer Risk: A Meta-Analysis of Published Epidemiological Studies

Studies investigating the association of milk consumption with bladder cancer risk have reported inconsistent findings. We conducted a meta-analysis of published cohort and case-control studies to pool the risk estimates of the association between milk intake and bladder cancer. We quantified associations with bladder cancer using meta-analysis of odds ratio (OR) associated with the highest vs. the lowest category of milk intake using fixed- or random-effect models depending on the heterogeneity of effects among studies. Nineteen cohort and case-control studies were eligible for inclusion. High milk intake was significantly associated with decreased risk of bladder cancer (OR, 0.84; 95% CI, 0.71–0.97) when comparing the highest with the lowest category of milk intake. The inverse association was stronger in Asia (OR, 0.60; 95% CI, 0.40–0.81) than North America (OR, 0.89; 95% CI, 0.76–1.03), and no association was observed in Europe (OR, 1.05; 95% CI, 0.85–1.26). This relationship also varied significantly by specific dairy products. Our results suggest that milk may be related to the reduction of bladder cancer risk. Further studies need to clarify the biological mechanisms.     

Folate intake and risk of bladder cancer: a meta-analysis of epidemiological studies

Epidemiological studies have reported conflicting results between folate intake and bladder cancer risk. We conducted a meta-analysis of epidemiological studies published between 1996 and June 2013 on the relationship between folate intake and bladder cancer. We quantified associations with bladder cancer using meta-analysis of risk estimates (REs) associated to the highest versus the lowest category of folate intake using random effect models. Seven cohort and six case-control studies were eligible for inclusion. A significantly decreased risk with bladder cancer was observed in overall folate intake group (RE?=?0.84; 95% CI, 0.72–0.96) and subgroup of case-control studies (RE?=?0.73; 95% CI, 0.57–0.89), but not in cohort studies (RE?=?0.96; 95% CI, 0.81–1.10) when comparing the highest with the lowest category of folate intake. No heterogeneity and publication bias were observed across studies. Although the current evidence, mainly based on data from case-control studies, supports an inverse association between folate intake and bladder cancer, additional large and well-designed cohort studies are needed before definitive conclusions can be drawn.     

Adherence to Dietary Approaches to Stop Hypertension (DASH)-Style Diet and the Risk of Cancer: A Systematic Review and Meta-Analysis of Cohort Studies

Abstract

Objective: Several investigators have proposed a protective association between dietary approaches to stop hypertension (DASH) style diet and risk of cancers; however, they have had inconsistent results. The present study aimed to systematically review the prospective cohort studies and if possible quantify the overall effect using meta-analysis.

Methods: PubMed, Scopus, and Google Scholar were searched for cohort studies published up to July 2018. Relative risks (RRs) that were reported for fully adjusted models and their confidence intervals were extracted for meta-analysis. The random effects model was used to combine the RRs.

Results: Seventeen studies were eligible to be included in the systematic review, from which nine reports assessed the association between the DASH diet and risk of mortality from all cancer types, four assessed incidence of colorectal cancer, and two studies assessed the risk of colon and rectal cancer separately. Four studies examined the association with the incidence of other cancers (breast, hepatic, endometrial, and lung cancer). Meta-analysis showed that high adherence to DASH is associated with a decreased mortality from all cancer types (RR = 0.84, 95% confidence interval [95%CI]: 0.81–0.86). Participants with the highest adherence to the DASH diet had a lower risk of developing colorectal (RR = 0.79, 95%CI: 0.75–0.83), colon (RR = 0.80, 95%CI: 0.74–0.87), and rectal (RR = 0.84, 95%CI: 0.74–0.96) cancers compared to those with the lowest adherence.

Conclusion: DASH-style diet should be suggested as a healthy approach associated with decreased risk of cancer in the community. Prospective studies exploring the association for other cancer types and from regions other than the United States are highly recommended.     

Soyfood intake in the prevention of breast cancer risk in women: a meta-analysis of observational epidemiological studies

Many studies have suggested that the intake of soy products may protect against the occurrence of breast cancer because of the considerable amount of isoflavones they contain. To review the results of the observational studies, we performed this meta-analysis of the relevant literature. We searched Medline for reports that examined the association between soyfood consumption (or isoflavone intake) and breast cancer risk from January 1966 to April 2006. The random-effects model was used to estimate the pooled relative risk (RR). Twenty-one independent studies (14 case-control studies and 7 cohort studies) were included in the final analysis. The pooled RR of breast cancer for soyfood intake was 0.75 with a 95% CI of 0.59-0.95. As the main types of soyfood in Japan and China, tofu and miso showed clear protective effects. Isoflavone intake resulted in a 20% decrease in risk (RR = 0.81, 95% CI 0.67-0.99). The pooled RR varied little according to study stratification. When the studies published in Japanese and Chinese were added, the inverse associations between soyfood, tofu and breast cancer risk became slightly stronger. The weak association of miso was possibly due to the high concentration of salt in miso soup. In the present analysis, we did not find strong evidence for publication bias in the combination of the studies. This meta-analysis supported the hypotheses that soyfood intake may be associated with a decreased risk of breast cancer due to the isoflavones. Further epidemiological studies need to be conducted with more comprehensive information about the soyfood, and more accurate assessment of the isoflavones.