Intake of fruits, vegetables, folic acid and related nutrients and risk of breast cancer in postmenopausal women

The association between dietary intakes of methionine, choline and betaine and breast cancer risk: A systematic review and meta-analysis

BACKGROUND AND AIM

This study evaluates the associations between dietary intakes and circulating blood levels of methionine, choline or betaine and breast cancer risk, which remains currently unclear.

METHODS

Systematic searches for observational epidemiological studies were performed of the MEDLINE, Embase, and Web of Science databases through July, 2022. Two review authors independently screened titles and abstracts against the eligibility criteria at a first stage, and screened full texts of potentially eligible records at a second stage, followed by data extraction from qualified studies. Quality of evidence was assessed using the Newcastle-Ottawa scale quality assessment tool. Risk estimates were calculated using random-effects meta-analysis.

RESULTS

In total, 21 studies were selected for qualitative analyses and 18 studies were included in the meta-analyses. Random-effects analysis combining prospective cohort (N = 8) or case-control studies (N = 10) showed little evidence of an association between dietary intake of methionine or betaine and the risk of breast cancer. However, inconclusive evidence for a significant inverse association between choline intake and breast cancer risk was found in case-control studies (odds ratio [OR] estimates for highest vs. lowest intakes = 0.38; 95 % CI: 0.16-0.86) but not in prospective cohort studies (hazard ratio [HR] estimates for highest vs. lowest intakes = 1.01; 95 % CI: 0.92-1.12).

CONCLUSION

This study did not suggest an effect of dietary intake of methionine, choline, nor betaine on breast cancer risk, mainly due to the lack of precision of the combined risk estimates as few studies are available. To overcome this uncertainty, more well-designed studies with relevant individual-level covariates are needed.

Association of folate intake and plasma folate level with the risk of breast cancer: a dose-response meta-analysis of observational studies

Epidemiological studies showing the correlation between folate and the breast cancer risk have revealed inconsistent results. Hence, we conducted a dose-response meta-analysis of observational studies to obtain more reliable conclusions. We searched PubMed and Embase for studies published before April 2019 and identified 39 studies on folate intake and 12 studies on plasma folate level. The combined odds ratios (ORs) and 95% confidence intervals (CIs) were extracted to estimate the breast cancer risk. Folate intake was inversely correlated with the breast cancer risk when the highest and lowest categories (OR = 0.85, 95% CI = 0.79-0.92) were compared, and the dose-response result showed that folate intake had a linear correlation with the breast cancer risk. Moreover, a higher folate intake correlated with a lower breast cancer risk in premenopausal women (OR = 0.80, 95% CI = 0.66-0.97), but not in postmenopausal women (OR = 0.94, 95% CI = 0.83-1.06). However, plasma folate levels were not correlated with the breast cancer risk (OR = 0.98, 95% CI = 0.82-1.17). Folate intake was negatively correlated with the breast cancer risk; however, its practical clinical significance requires further study. Furthermore, additional folate supplements should be considered carefully.

Folate intake and the risk of breast cancer: a systematic review and meta-analysis

There is conflicting epidemiological evidence on the role of folate and breast cancer risk. We conducted a systematic review and quantitative meta-analysis of folate intake and folate blood levels and the risk of breast cancer. Four electronic databases (Medline, PubMed, Embase, and Current Contents Connect) were searched to April 11, 2014, with no language restrictions for observational studies that measured folate intake or blood levels and the risk of breast cancer. The meta-analysis of dietary folate intake comprising 36 studies with 34,602 cases, and a total sample size of 608,265 showed a decreased risk of breast cancer, with an odds ratio (OR) of 0.84 [95 % confidence interval (CI) 0.77-0.91]. When stratified by menopausal status and by study design, none of the meta-analyses of prospective studies showed any statistically significant decrease in the risk of breast cancer. The meta-analysis of total folate showed no statistically significant association with breast cancer OR of 0.98 (95 % CI 0.91-1.07). There was no significant association between either dietary or total folate intake and breast cancer when stratified by hormonal receptor status. The meta-analysis of blood folate levels found no significant association with the risk of breast cancer, with an OR of 0.86 (95 % CI 0.60-1.25). Breast cancer does not appear to be associated with folate intake, and this did not vary by menopausal status or hormonal receptor status. Folate blood levels also do not appear to be associated with breast cancer risk.

Higher dietary folate intake reduces the breast cancer risk: a systematic review and meta-analysis

Background:

Many epidemiological studies have investigated the association between folate intake, circulating folate level and risk of breast cancer; however, the findings were inconsistent between the studies.

Methods:

We searched the PubMed and MEDLINE databases updated to January, 2014 and performed the systematic review and meta-analysis of the published epidemiological studies to assess the associations between folate intake level, circulating folate level and the overall risk of breast cancer.

Results:

In all, 16 eligible prospective studies with a total of 744 068 participants and 26 205 breast cancer patients and 26 case–control studies with a total of 16 826 cases and 21 820 controls that have evaluated the association between folate intake and breast cancer risk were identified. Pooled analysis of the prospective studies and case–control studies suggested a potential nonlinearity relationship for dietary folate intake and breast cancer risk. Prospective studies indicated a U-shaped relationship for the dietary folate intake and breast cancer risk. Women with daily dietary folate intake between 153 and 400 μg showed a significant reduced breast cancer risk compared with those <153 μg, but not for those >400 μg. The case–control studies also suggested a significantly negative correlation between the dietary folate intake level and the breast cancer risk. Increased dietary folate intake reduced breast cancer risk for women with higher alcohol intake level, but not for those with lower alcohol intake. No significant association between circulating folate level and breast cancer risk was found when the results of 8 identified studies with 5924 participants were pooled.

Conclusions:

Our studies suggested that folate may have preventive effects against breast cancer risk, especially for those with higher alcohol consumption level; however, the dose and timing are critical and more studies are warranted to further elucidate the questions.

Association of vitamin B6, vitamin B12 and methionine with risk of breast cancer: a dose-response meta-analysis

Background:

Epidemiological studies evaluating the association of vitamin B₆, vitamin B₁₂ and methionine with breast cancer risk have produced inconsistent results.

Methods:

Pertinent studies were identified by a search in PubMed and Web of Knowledge. Random-effect model was used. Dose–response relationship was assessed by restricted cubic spline.

Results:

The combined relative risk (95% confidence interval) of breast cancer for the highest vs lowest category of serum pyridoxal 5′-phosphate (PLP, active form of vitamin B₆) levels and dietary methionine intake was 0.80 (0.66–0.98, P=0.03) and 0.94 (0.89–0.99, P=0.03), respectively, and the associations of breast cancer with higher serum PLP levels and dietary methionine intake were significant among post-menopausal women, but not among pre-menopausal women. The inverse association between breast cancer risk and dietary vitamin B₆ intake, serum vitamin B₁₂ levels and dietary vitamin B₁₂ intake was not significant overall. Linear dose–response relationship was found, and the risk of breast cancer decreased by 23% (P<0.00) for every 100 pmol ml⁻¹ increment in PLP levels and 4% (P=0.05) for every 1 g per day increment in dietary methionine intake, respectively.

Conclusion:

Serum PLP levels and methionine intake might be inversely associated with breast cancer risk, especially among postmenopausal women, which need to be confirmed.

Dietary folate, vitamin B6, vitamin B12 and methionine intake and the risk of breast cancer by oestrogen and progesterone receptor status

Few studies have evaluated the relationship between the consumption of dietary folate and one-carbon metabolism-related nutrients and breast cancer risk defined by oestrogen receptor (ER) and progesterone receptor (PR) status. The objective of the present study was to examine the associations between dietary folate, vitamin B6, vitamin B12, and methionine intake and the risk of breast cancer by ER and PR status among Chinese women in Guangdong. A hospital-based case–control study was conducted from June 2007 to August 2008, with 438 cases and 438 age (5-year interval)- and residence (rural/urban)-matched controls. Dietary intake information was assessed using a validated FFQ administered through a face-to-face interview. Unconditional logistic regression models were used to calculate multivariate-adjusted OR and 95 % CI. A significant inverse association was found between dietary folate and vitamin B6 intake and breast cancer risk. The adjusted OR of the highest v. the lowest quartile were 0·32 (95 % CI 0·21, 0·49; Ptrend < 0·001) for dietary folate and 0·46 (95 % CI 0·30, 0·69; Ptrend < 0·001) for vitamin B6. No associations were observed for vitamin B12 and methionine intake. A significant inverse association between dietary folate intake and breast cancer risk was observed in all subtypes of ER and PR status. These findings suggest that dietary folate and vitamin B6 intakes were inversely associated with breast cancer risk. The inverse association did not differ by ER and/or PR status.

Folate and other one-carbon metabolism-related nutrients and risk of postmenopausal breast cancer in the Cancer Prevention Study II Nutrition Cohort

BACKGROUND

Epidemiologic studies of the association of folate intake with breast cancer risk have been inconclusive, and few have investigated how related nutrients modify this association.

OBJECTIVE

We investigated the association of dietary (food folate plus folic acid from fortification) and total folate (food folate, folic acid from fortification, and folic acid from supplements), vitamin B-6, vitamin B-12, methionine, and alcohol intakes with postmenopausal breast cancer among women in the Cancer Prevention Study II Nutrition Cohort. The modification of the folate associations by the other nutrients was also investigated.

DESIGN

This prospective cohort study included 70,656 postmenopausal women for whom dietary information was collected in 1992. Of these, 3898 developed breast cancer between enrollment in 1992 and June 2005. Cox proportional hazards modeling was used to calculate multivariate-adjusted hazard rate ratios and 95% CIs.

RESULTS

Compared with the lowest quintile, the highest quintile of dietary folate intake was associated with a higher risk of breast cancer (rate ratio: 1.12; 95% CI: 1.01, 1.24). However, the test for trend was not significant (P for trend = 0.15). No association was found for total folate, vitamin B-6, or vitamin B-12, but methionine was inversely associated with breast cancer risk (P for trend = 0.04). The association of dietary folate with breast cancer was not modified by other nutrients or alcohol.

CONCLUSIONS

This study suggests that dietary folate intake may be positively associated with postmenopausal breast cancer. However, no dose-response relation was observed. The extent to which increased supplement use and folate fortification contributes to breast cancer risk warrants further research.

Food-frequency questionnaires: a review of their design, validation and utilisation

A review of the literature concerning the design, utilisation and validation of food-frequency questionnaires (FFQ) has been carried out using a semi-systematic approach to obtaining, reviewing and extracting data from articles. Databases were searched from 1980 to 1999. The present review identified 227 validation (from 1980 to September 1999) and 164 utilisation (for 1998 only) studies. A number of design issues have been evaluated through the present review. These include: the need to consider how portion sizes have been described, self-defined giving higher mean correlations; how an FFQ was administered, interviewer-administered giving higher mean correlations for some nutrients; how many items to include on an FFQ, those with the largest number of items having higher correlations. Validation techniques were described. Most validation studies involved comparing an FFQ against another dietary assessment method; only 19 % compared an FFQ to a biomarker. Measurement differences were most commonly assessed by correlation coefficients as opposed to other more appropriate methods. Mean correlation coefficients were highest for Ca and fat, and lowest for vitamin A and vegetables. The utilisation studies showed that FFQ were most commonly used in cross-sectional surveys, with ninety-three of the FFQ being designed to be disease-specific. The present review results were presented to a group of experts and a consensus arrived at concerning the development, validation and use of FFQ. Recommendations derived from the consensus arising from the literature review are presented as an appendix to the present paper.

Greater vegetable and fruit intake is associated with a lower risk of breast cancer among Chinese women

The effect of vegetable and fruit consumption on breast cancer risk is controversial. We examined the association between vegetable and fruit intake and breast cancer risk in a hospital-based case-control study conducted in Guangdong, China. Four hundred and thirty-eight cases were frequency matched to 438 controls by age (5-year interval) and residence (rural/urban). Dietary intake was assessed by face-to-face interviews using a validated food frequency questionnaire. Multivariate logistic regression was used to estimate the odds ratios (ORs) and 95% confidence interval (CI) after adjusting for various potential confounders. Total vegetable and fruit intake was found to be inversely associated with breast cancer risk. The ORs of the highest quartile relative to the lowest quartile of total vegetable and fruit intake were 0.28 (95% CI 0.18-0.43) and 0.53 (95% CI 0.34-0.82), respectively. Consumption of individual vegetable and fruit groups such as dark green leafy vegetables, cruciferous vegetables, carrots and tomatoes, banana, watermelon/papaya/cantaloupe were all inversely and significantly related with breast cancer risk. An inverse association was also observed for vitamin A, carotene, vitamin C, vitamin E, and fiber intake. These data indicate that greater intake of vegetables and fruits is associated with a decreased risk of breast cancer among Chinese women residing in Guangdong.

Folate and one-carbon metabolism nutrients from supplements and diet in relation to breast cancer risk

BACKGROUND

Few epidemiologic studies have examined very high intakes of folate and whether consumption of nutrients involved in one-carbon metabolism is associated with breast cancer risk.

OBJECTIVE

We prospectively examined whether the consumption of folate and nutrients involved in one-carbon metabolism (methionine, riboflavin, and vitamins B-6 and B-12) from self-reported intakes of diet (in year before baseline) and supplements (averaged over 10 y before baseline) were associated with the incidence of breast cancer and breast cancer tumor characteristics.

DESIGN

Participants were 35,023 postmenopausal women aged 50-76 y in the VITamins And Lifestyle (VITAL) cohort study; breast cancer was diagnosed in 743 of these women between baseline (2000-2002) and 2006. Cox proportional hazards models were used to estimate multivariable-adjusted relative risks (RRs) and 95% CIs.

RESULTS

Women consuming > or =1272 dietary folate equivalents (DFE)/d of total folate (10-y average) had a 22% decrease in breast cancer risk compared with women consuming < or =345 DFE/d (RR: 0.78; 95% CI: 0.61, 0.99; P for trend = 0.05). A greater benefit was observed for estrogen-receptor (ER) negative than for ER+ breast cancers (RR: 0.38; 95% CI: 0.18, 0.80; P for trend = 0.02; P = 0.02 for the difference between ER- and ER+). Neither current intakes of folate nor current or long-term intakes of other one-carbon nutrients were significantly associated with breast cancer risk. Multivitamin use attenuated the increased risk of breast cancer associated with alcohol drinking (P for interaction = 0.02).

CONCLUSIONS

Our study of predominantly supplement users suggests that high intakes of folate averaged over 10 y do not increase breast cancer risk, but may be protective, particularly against ER- breast cancers.

Dietary intake of selected B vitamins in relation to risk of major cancers in women

Although folic acid has been investigated for its potential to inhibit carcinogenesis, few epidemiologic studies have assessed the effects of intake of thiamin, riboflavin, and niacin, which may reduce cancer risk by acting as cofactors in folate metabolism or by other mechanisms. Using data from a large cohort of Canadian women, we examined the association of dietary intake of these nutrients, as well as intake of folate, methionine, and alcohol, with cancers of the breast, endometrium, ovary, colorectum, and lung ascertained during an average of 16.4 years of follow-up. After exclusions, the following numbers of incident cases were available for analysis: breast, n=2491; endometrium, n=426; ovary, n=264; colorectum, n=617; and lung, n=358. Cox proportional hazard models were used to estimate risk of each cancer with individual nutrients and to explore possible effect modification by combinations of nutrients on cancer risk. Few significant associations of intake of individual B vitamins with the five cancers were observed. Alcohol consumption showed a modest positive association with breast cancer risk but not with risk of the other cancers. There was no evidence of effect modification among the nutrients. This large study provides little support for an association of dietary intake thiamin, riboflavin, niacin, folate, or methionine with five major cancers in women.

Plasma folate, vitamin B-6, vitamin B-12, and risk of breast cancer in women

BACKGROUND

B vitamins such as folate, vitamin B-6, and vitamin B-12 are coenzymes that are important for DNA integrity and stability. Deficiency in these B vitamins may promote tumor carcinogenesis.

OBJECTIVE

We prospectively evaluated plasma concentrations of folate, pyridoxal 5-phosphate (PLP; the principal active form of vitamin B-6), and vitamin B-12 in relation to breast cancer risk.

DESIGN

We included 848 incident cases of invasive breast cancer identified as of 31 March 2004, and 848 individually matched control subjects from 28 345 women in the Women's Health Study aged > or =45 y who provided blood samples and had no history of cancer and cardiovascular disease at baseline in 1993. Logistic regression controlling for matching factors and other risk factors for breast cancer was used to estimate relative risks (RRs) and 95% CIs. All statistical tests were 2 sided.

RESULTS

Plasma concentrations of folate, PLP, and vitamin B-12 were not associated with overall risk of breast cancer. Women in the highest quintile group relative to those in the lowest quintile had multivariate RRs of 1.42 (95% CI: 1.00, 2.02) for plasma folate (P for trend = 0.21), 0.91 (95% CI: 0.63, 1.30) for plasma PLP (P for trend = 0.48), and 1.29 (95% CI: 0.92, 1.82) for plasma vitamin B-12 (P for trend = 0.18). However, higher plasma folate concentrations were moderately associated with an increased risk of developing premenopausal breast cancer (P for trend = 0.04) and for developing estrogen receptor (ER)-positive or progesterone receptor (PR)-positive breast tumors (P for trend < or = 0.06). Conversely, an inverse association was seen between plasma PLP and postmenopausal breast cancer (P for trend = 0.04).

CONCLUSIONS

Data from this study suggest that B vitamins, including folate, vitamin B-6, and vitamin B-12, may confer little or no reduction in overall risk of developing breast cancer. The observed positive associations of folate status with risk of developing premenopausal breast cancer and ER-positive or PR-positive tumors are unexpected. Additional research is needed to elucidate the role of folate in breast cancer development.

Increasing folate supplementation for selected groups of Canadian women

After review of current evidence related to the potential risks and benefits of folic acid supplementation, we conclude that unless clinicians can be assured that pregnant women will reliably use prenatal vitamin supplements containing 0.8-1.1 mg of folate, the prenatal vitamin supplements should be combined with 5 mg of folate.

Dietary intake and status of folate and vitamin B12 and their association with homocysteine and cardiovascular disease in European populations

BACKGROUND/OBJECTIVES

Folate and vitamin B12 have been suggested to play a role in chronic diseases like cardiovascular diseases. The objectives are to give an overview of the actual intake and status of folate and vitamin B12 in general populations in Europe, and to evaluate these in view of the current vitamin recommendations and the homocysteine concentration.

METHODS

Searches in Medline with 'folic acid', 'folate' and 'vitamin B12', 'B12' or 'cobalamin' as key words were combined with the names of the European countries. Populations between 18 and 65 years were included.

RESULTS

Sixty-three articles reporting on studies from 15 European countries were selected. Low folate intakes were observed in Norway, Sweden, Denmark and the Netherlands. Low intakes of vitamin B12 were not common and only seen in one small Greek study. In the countries with a low intake of folate, the recommended levels were generally not achieved, which was also reflected in the folate status. Vitamin B12 intake was not strongly associated with the vitamin B12 status, which can explain why in the Netherlands and Germany the vitamin B12 status was inadequate, despite sufficient intake levels. In countries with a low folate intake in particular, the Hcy concentration was higher than ideal.

CONCLUSIONS

Populations from the Nordic countries, the Netherlands, Germany and Greece may need to improve their intakes of folic acid, B12 or both to either meet the recommendations or to optimize their statuses. This could be achieved via a food-based approach, food fortification or supplements.

High folate intake is associated with lower breast cancer incidence in postmenopausal women in the Malmö Diet and Cancer cohort

BACKGROUND

Epidemiologic studies of associations between folate intake and breast cancer are inconclusive, but folate and other plant food nutrients appear protective in women at elevated risk.

OBJECTIVE

The objective was to examine the association between folate intake and the incidence of postmenopausal breast cancer.

DESIGN

This prospective study included all women aged >or=50 y (n = 11699) from the Malmö Diet and Cancer cohort. The mean follow-up time was 9.5 y. We used a modified diet-history method to collect nutrient intake data. At the end of follow-up, 392 incident invasive breast cancer cases were verified. We used proportional hazard regression to calculate hazard ratios (HRs).

RESULTS

Compared with the lowest quintile, the incidence of invasive breast cancer was reduced in the highest quintile of dietary folate intake (HR: 0.56; 95% CI: 0.35, 0.90; P for trend = 0.02); total folate intake, including supplements (HR: 0.56; 95% CI: 0.34, 0.91; P for trend = 0.006); and dietary folate equivalents (HR: 0.59; 95% CI: 0.36, 0.97; P for trend = 0.01).

CONCLUSION

A high folate intake was associated with a lower incidence of postmenopausal breast cancer in this cohort.

Folate and risk of breast cancer: a meta-analysis

BACKGROUND

Epidemiologic findings are inconsistent concerning risk for breast cancer associated with low folate intake or blood folate levels. We performed a meta-analysis of prospective and case-control studies to examine folate intake and levels in relation to risk of breast cancer.

METHODS

We searched MEDLINE for studies of this association that were published in any language from January 1, 1966, through November 1, 2006. Study-specific risk estimates were pooled by use of a random-effects model. All statistical tests were two-sided.

RESULTS

Folate intake in increments of 200 microg/day was not associated with the risk of breast cancer in prospective studies (estimated summary relative risk [RR] = 0.97, 95% confidence interval [CI] = 0.88 to 1.07, for dietary folate [eight studies; 302,959 participants and 8367 patients with breast cancer], and RR = 1.01, 95% CI = 0.97 to 1.05, for total folate [six studies; 306,209 participants and 8165 patients with breast cancer]) but was statistically significantly inversely associated with risk in case-control studies (estimated summary odds ratio [OR] = 0.80, 95% CI = 0.72 to 0.89, for dietary folate [13 studies; 8558 case patients and 10,812 control subjects], and OR = 0.93, 95% CI = 0.81 to 1.07, for total folate [three studies; 2184 case patients and 3233 control subjects]). High blood folate levels versus low levels were not statistically significantly associated with the risk of breast cancer in prospective studies (OR = 0.81, 95% CI = 0.59 to 1.10 [three studies]) or in case-control studies (OR = 0.41, 95% CI = 0.15 to 1.10 [two studies]). Among the two prospective studies and two case-control studies that stratified by alcohol consumption, high folate intake (comparing the highest with the lowest category) was associated with a statistically significant decreased risk of breast cancer among women with moderate or high alcohol consumption (summary estimate = 0.51, 95% CI = 0.41 to 0.63) but not among women with low or no alcohol consumption (summary estimate = 0.95, 95% CI = 0.78 to 1.15). Few studies examined whether the relation between folate intake and breast cancer was modified by intakes of methionine or vitamins B6 and B12, and the findings were inconsistent.

CONCLUSION

No clear support for an overall relationship between folate intake or blood folate levels and breast cancer risk was found. Adequate folate intake may reduce the increased risk of breast cancer that has been associated with moderate or high alcohol consumption.

Meta-analyses of Observational and Genetic Association Studies of Folate Intakes or Levels and Breast Cancer Risk

BACKGROUND

Evidence from case-control studies suggests that increasing dietary folate intake is associated with a reduced risk of breast cancer. However, large cohort studies have found no such association, and animal studies suggest that folate supplementation may promote tumorigenesis. We conducted a meta-analysis to summarize the available evidence from observational studies on this issue and a meta-analysis of the association between a common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, a key enzyme in folate metabolism, and breast cancer risk.

METHODS

We searched Medline and ISI Web of Knowledge databases for relevant studies that were published through May 31, 2006. We used random-effects analysis to calculate odds ratios (ORs) for case-control studies or relative risks (RRs) for cohort studies for a 100-microg/d increase in folate intake. Unadjusted odds ratios were calculated for the studies of MTHFR genotype based on published genotype frequencies.

RESULTS

A total of 13 case-control studies and nine cohort studies were included in the meta-analysis of folate intake and breast cancer risk. We found a summary OR of 0.91 (95% confidence interval [CI] = 0.87 to 0.96) from the case-control studies and a summary RR of 0.99 (95% CI = 0.98 to 1.01) from the cohort studies for a 100-microg/d increase in folate intake. We found evidence that the case-control studies may have suffered from substantial publication bias. The case-control and cohort studies may have been subject to measurement error, confounding, and possibly spurious associations arising from subgroup analyses; in addition, the case-control studies were potentially subject to recall bias and publication bias. Seventeen studies were included in the meta-analysis of MTHFR C677T genotype and breast cancer risk. We found no difference in breast cancer risk between MTHFR 677 TT homozygotes and CC homozygotes (OR = 1.05, 95% CI = 0.88 to 1.25), and there was no evidence of an interaction between folate intake and MTHFR genotype on breast cancer risk.

CONCLUSION

A lack of dietary folate intake is not associated with the risk of breast cancer.

Fruit and vegetables in cancer prevention

Our aim was to review the epidemiological literature on possible cancer-preventive effects of the consumption of fruits and vegetables in humans, to quantify the effect of high versus low consumption of fruits and vegetables, and to give an overall assessment of the existing evidence. We based our work on an expert meeting conducted by the International Agency for Research on Cancer in 2003. A qualitative reading and evaluation of relevant articles on the cancer-preventive effect of the consumption of fruits and vegetables was made followed by the calculation of the mean relative risk and range for cohort and case-control studies separately. The possible population-preventable fraction for modifying diet in relation to fruit and vegetable consumption was calculated as well as an overall statement about the degree of evidence for the cancer-preventive effect of fruit and vegetable consumption for each cancer site. There is limited evidence for a cancer-preventive effect of the consumption of fruits and vegetables for cancer of the mouth and pharynx, esophagus, stomach, colon-rectum, larynx, lung, ovary (vegetables only), bladder (fruit only), and kidney. There is inadequate evidence for a cancer-preventive effect of the consumption of fruits and vegetables for all other sites. Applying this range of risk difference to the range of prevalence of low intake, the preventable fraction for low fruit and vegetable intake would fall into the range of 5-12%. It is important to recognize that this is only a crude range of estimates and that the proportion of cancers that might be preventable by increasing fruit and vegetable intake may vary beyond this range for specific cancer sites and across different regions of the world.

Folate, vitamin B(6), and vitamin B(12) intake and the risk of breast cancer among Mexican women

BACKGROUND

High intake of folate, vitamin B(6), and vitamin B(12) have been hypothesized to lower the risk for breast cancer. We conducted a population-based case-control study to evaluate the risk for breast cancer among Mexican women with relatively low vitamin intakes.

METHODS

We included 475 women (median age, 53 years; range, 23-87 years) diagnosed with incident breast cancer through six hospitals in Mexico City and interviewed them to obtain data on breast cancer risk factors and their usual diet using a food frequency questionnaire. We selected 1,391 (median age, 49 years; range, 18-82 years) controls from the Mexico City population using a national sampling frame.

RESULTS

Compared with women in the lowest quartile, the odds ratio for breast cancer for women in the highest quartile of folate intake was 0.64 [95% confidence intervals (CI), 0.45-0.90; P, test for trend = 0.009] and 0.32 (95% CI, 0.22-0.49; P, test for trend < 0.0001) for vitamin B(12) intake. Among postmenopausal women, intakes of folate and vitamin B(12) were associated with a lower risk of breast cancer and those associations were stronger than among premenopausal women. The inverse association of folate and breast cancer was stronger among women who consumed a high level of vitamin B(12) as compared with women consuming diets low in vitamin B(12). No association was observed for vitamin B(6) intake.

CONCLUSIONS

In this population, high intakes of folate and vitamin B(12) were independently associated with decreased breast cancer risk, particularly among postmenopausal women.

Folate intake, alcohol and risk of breast cancer among postmenopausal women in Denmark

OBJECTIVE

There is consistent evidence that alcohol increases the risk of breast cancer. It has been suggested that the increased risk associated with alcohol intake may be reduced by adequate intake of folate. Since many women consume alcohol, detection of a risk-reducing mechanism would have major public health implications.

DESIGN

We therefore evaluated the possible interaction between alcohol and folate in a paired nested case-control study among postmenopausal women.

SETTING

A total of 24 697 postmenopausal women were included in the 'Diet, Cancer and Health' follow-up study between December 1993 and May 1997. The cohort was followed until December 2000. The study included 388 cases of breast cancer and 388 randomly selected controls were used to estimate the breast cancer incidence rate ratio (IRR) in conditional logistic regression analysis.

RESULTS

A previously established association between alcohol intake and risk of breast cancer was present mainly among women with low folate intake. An IRR of 1.19 (95% CI: 0.99-1.42) per 10 g average daily alcohol intake was found for women with a daily folate intake below 300 mug, while among women with a folate intake higher than 350 mug, we could not show an association between the alcohol intake and the breast cancer incidence rate (e.g. folate intake >400 mug; IRR of 1.01 (95% CI: 0.85-1.20)).

CONCLUSION

The findings support the evidence that adequate folate intake may attenuate the risk of breast cancer associated with high alcohol intake.

SPONSORSHIP

The Danish Cancer Society.

Folate intake, alcohol use, and postmenopausal breast cancer risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial

BACKGROUND

Several epidemiologic studies suggest that higher folate intakes are associated with lower breast cancer risk, particularly in women with moderate alcohol consumption.

OBJECTIVE

We investigated the association between dietary folate, alcohol consumption, and postmenopausal breast cancer in women from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial cohort.

DESIGN

Dietary data were collected at study enrollment between 1993 and 2001. Folate content was assigned on the basis of prefortification (ie, pre-1998) databases. Of the 25 400 women participants with a baseline age of 55-74 y and with complete dietary and multivitamin information, 691 developed breast cancer between September 1993 and May 2003. We used Cox proportional hazard models with age as the underlying time metric to generate hazard ratios (HRs) and 95% CIs.

RESULTS

The adjusted HRs were 1.19 (95% CI: 1.01, 1.41; P for trend = 0.04) for women reporting supplemental folic acid intake >/=400 mug/d compared with subjects reporting no supplemental intake. Comparison of the highest with the lowest quintile gave adjusted HRs of 1.04 (95% CI: 0.83, 1.31; P for trend = 0.56) and 1.32 (95% CI: 1.04, 1.68; P for trend = 0.03) for food and total folate intake, respectively. Alcohol consumption was positively associated with breast cancer risk (highest compared with lowest quintile: HR = 1.37; 95% CI: 1.08, 1.76; P for trend = 0.02); the risk was greatest in women with lower total folate intake.

CONCLUSIONS

Our results do not support the hypothesis that high folate intake reduces breast cancer risk; instead, they suggest that a high intake, generally attributable to supplemental folic acid, may increase the risk in postmenopausal women. However, our results confirm previous studies showing positive associations between moderate alcohol consumption and breast cancer.

Investigation of systemic folate status, impact of alcohol intake and levels of DNA damage in mononuclear cells of breast cancer patients

Folate is required for DNA synthesis, repair and methylation. Low folate status has been implicated in carcinogenesis, possibly as a result of higher rate of genetic damage. The aim of this study is to compare folate status and levels of DNA damage between breast cancer and benign breast disease control patients. Fasting blood samples from 64 histologically confirmed untreated breast cancer patients (mean age 57 years) and 30 benign breast disease control patients (mean age 51 years) were obtained. Red cell folate (RCF) and plasma homocysteine were measured. Mononuclear cells (MNC) were isolated for genetic damage analysis using the basic alkaline comet assay. Results are expressed as tail moment. Data were log transformed as appropriate before analysis for normalisation purposes. The geometric mean (95% confidence interval) of RCF (ng ml⁻¹) in breast cancer patients was 339.07 (333.3–404.6) vs 379.5 (335.8–505.2) in control patients (P=0.24). Corresponding plasma homocysteine concentrations (μmol l⁻¹) were 11.9 (10.6–16.4) vs 10.1 (9.3–11.9) (P=0.073), respectively. The mean tail moment (s.d.) of DNA damage in MNC of breast cancer patients detected by the basic comet assay was 1.4 (0.66) vs –0.17 (0.79) in controls (P<0.0001, t-test), the modified comet assay ‘endonuclease III (Endo III)’ was 1.7 (0.70) vs 0.86 (0.81) (P<0.0001, t-test), and the modified comet assay ‘formamidopyrimidine glycosylase (FPG)’ was 1.6 (0.62) vs 0.99 (0.94) (P<0.0001, t-test). There was a significant negative correlation between RCF levels and DNA damage detected by modified comet assay ‘FPG’ (Pearson Correlation Coefficient r²=−0.26, P=0.02) and DNA damage was found to be significantly higher in MNC of breast cancer patients compared to benign breast disease control patients. Breast cancer patients tended to have lower RCF levels and higher levels of plasma homocysteine, but these differences were not significant. The study provides preliminary evidence that reduced folate status may be implicated in the aetiology of breast cancer perhaps by increasing the in vivo level of genetic instability.

Effects of dietary folate on the development and progression of mammary tumors in rats

Epidemiologic studies have suggested that dietary intake and blood levels of folate may be inversely related to the risk of breast cancer. However, epidemiologic evidence has not been consistent nor has it provided unequivocal support for this purported inverse relationship. Recent evidence has also raised a concern that folate supplementation may promote carcinogenesis if provided after neoplastic foci are established in the target organ. This study investigated the effect of dietary folate deficiency and supplementation on the development and progression of mammary tumors in the N-methyl-N-nitrosourea (MNU) rat model. Weanling, female Sprague-Dawley rats were fed diets containing 0, 2 (control) or 8 mg folic acid/kg diet during the initiation or the promotion phase of MNU-induced mammary tumorigenesis. At necropsy, all macroscopic mammary tumors were identified and histologically confirmed. Dietary folate deficiency and supplementation provided during the initiation phase did not significantly modulate the development of mammary tumors. In contrast, dietary folate deficiency provided during the promotion phase significantly inhibited the rate of appearance, incidence, mean volume and weight of adenocarcinomas compared with the control and supplemental diets. Folate supplementation provided during the promotion phase did not significantly modulate mammary tumorigenesis compared with the control group. These data indicate that moderate folate deficiency inhibits, whereas dietary folate supplementation at four times the basal dietary requirement does not promote, the progression of MNU-induced mammary neoplastic foci in this rat model. However, the limitations associated with the route and dose of MNU administration preclude a definitive conclusion concerning the effect of folate status on the initiation of MNU-induced mammary tumorigenesis.

Reduced breast cancer risk with increasing serum folate in a case-control study of the C677T genotype of the methylenetetrahydrofolate reductase gene

Breast cancer risk may be associated with folate status or the C677T genotype of the methylenetetrahydrofolate reductase (MTHFR) gene. We compared serum folate concentrations and C677T genotype in 141 breast cancer patients and 109 age-matched controls. Serum folate was significantly lower in cases compared to controls (geometric means, 5.7 versus 6.6 microg/l; P=0.005). Breast cancer risk was not associated with C677T genotype. After adjusting for age of menarche, parity, alcohol intake and total fat intake we observed reductions in odds ratios for breast cancer risk comparing the highest with the lowest quartiles of serum folate concentrations of 0.23 (95% confidence interval (CI) 0.09, 0.54) for the entire group, 0.27 (CI 0.09, 0.80) for the wild-type and 0.08 (CI 0.01, 0.52) for the heterozygous C677T genotype. We conclude that for the whole group, and the wild-type and heterozygous C677T genotypes, increased serum concentrations of folate were associated with reduced risks of breast cancer.

MTHFR polymorphisms, dietary folate intake, and breast cancer risk: results from the Shanghai Breast Cancer Study

Folate plays an important role in DNA methylation, synthesis, and repair; intake has been associated with breast cancer. The folate-metabolizing enzyme, methylenetetrahydrofolate reductase (MTHFR) is polymorphic at nucleotides 677 (C-->T) and 1298 (A-->C), resulting in allozymes with decreased activity. We evaluated these two common polymorphisms and their effects on the folate intake and breast cancer risk association in a population-based case-control study of 1144 breast cancer cases and 1236 controls using a PCR-RFLP-based assay. All subjects completed in-person interviews, which included a food frequency questionnaire. Unconditional logistic regression models were used to calculate odds ratios and their 95% confidence intervals, after adjusting for potential confounding factors. Cases and controls were similar in the distribution of MTHFR polymorphisms at codons 677 (41.4% cases and 41.8% controls carried the T allele) and 1298 (17.6% cases and 17.5% controls carried the C allele). An inverse association of breast cancer risk with folate intake was observed in all genotype groups, particularly among subjects with the 677TT genotype. Compared with those with the 677CC genotype and high folate, the adjusted odds ratios (95% confidence intervals) associated with low folate intake were 1.94 (1.15-3.26), 2.17 (1.34-3.51), and 2.51 (1.37-4.60) for subjects who had CC, CT, and TT genotypes (p for interaction, 0.05). No modifying effect of A1298C genotypes on the association of folate intake with breast cancer risk was observed. Results of this study suggest that the MTHFR C677T polymorphisms may modify the association between dietary folate intake and breast cancer risk.

Food groups and colon cancer risk in African-Americans and Caucasians

The disparities in colon cancer incidence between African-Americans and other U.S. ethnic groups are largely unexplained. This report examines associations of various food groups with colon cancer in African-Americans and Caucasians from a case-control study. Incident cases of histologically confirmed colon cancer, age 40-80 years, (n = 613) and matched controls (n = 996) were interviewed in-person to ascertain potential colon cancer risk factors. Diet over the year before diagnosis or interview date was assessed using a validated food frequency questionnaire adapted to include regional foods. Multivariate logistic regression models estimated energy-adjusted and non-energy adjusted odds ratios (OR). Controls generally reported higher consumption (daily amount and weekly frequency) of fruits, vegetables and dark green, deep yellow fruits/vegetables, whereas cases consumed more refined carbohydrates and fats, oils and snacks. Regardless of ethnic group or energy adjustment, high and frequent vegetable consumption (particularly dark green vegetables) was protective, consistent with 20-50% reductions in risk. In Caucasians, high refined carbohydrate and red meat consumption (amount and frequency) was associated with a statistically significant 2-fold increased risk in non-energy adjusted models. In African-Americans, frequent intake of dairy foods was associated with a doubling in risk (OR = 1.9, 95% CI = 1.1-3.4) in non-energy-adjusted models, whereas frequent fruit consumption correlated with a non-significant 30% lower risk. These findings add to growing evidence that plant foods may protect against colon cancer; however, the effects of the other food groups varied by ethnic group and energy adjustment. These results may also explain some of the ethnic differences in colon cancer incidence.

The Role of Nutrition in the Prevention of Breast Cancer

Nutrition has been widely studied as a leading environmental factor in the prevention of breast cancer (BC). Despite the challenges in relating consumption of specific nutrients to BC risk, particularly in the context of a total diet, many investigators have contributed valuable information. Dietary fat has received the most attention and also created the most uncertainty. Specific types of fat, particularly monounsaturated fat and the ratio of omega-3 to omega-6 fatty acids, demonstrate more potential to influence BC risk. A wide variety of other dietary factors have been studied in relation to BC including total energy, dietary fiber, alcohol, micronutrients, phytochemicals, specific foods, and food constituents. Results of epidemiological studies relating consumption of these dietary factors to BC have increased the knowledge base that provides rationale for various nutritional strategies to contribute to BC prevention.

Social diversity of Irish adults nutritional intake

OBJECTIVE

The first health and lifestyle survey of Irish adults was carried out in 1998 and aimed to describe the health-related lifestyle behaviours of a cross-section of various population strata residing in the Republic of Ireland. This paper reports on the social variation in nutrient intake.

DESIGN

A self-administered postal questionnaire, including a 149 food item semiquantitative food frequency section, from which nutrient intakes were estimated based on McCance and Widdowson food composition tables.

SETTING

Community-based adults aged 18 years and over residing in the Republic of Ireland on the Register of Electors.

SUBJECTS

A stratified sample of adults on the Register of Electors received the questionnaire, of which 6539 (62%) were returned.

RESULTS

The contribution of fat to total energy intake increased with decreasing socioeconomic grouping, a finding reflective of the higher consumption levels of foods high in fat by respondents from socially disadvantaged groups. Energy from carbohydrates was greatest among those from socially advantaged groups, and was close to the recommended 50% of the total energy intake. Conversely, energy from protein decreased with increasing social status group. The mean intake of vitamins and minerals was generally close to or above the recommended values. Significant variation was observed among females across the different levels of education, whereas living with someone appeared to influence the micronutrient intake of males. The reported diets of males and females over the age of 65 years were lacking in vitamin D. Mean calcium levels among males were borderline and females over the age of 65 years had mean dietary iron levels below the recommended intake.

CONCLUSIONS

For the first time, quantification of nutrient intake in the different social groups in Ireland has been undertaken. A healthy balance of energy derived from fat, protein and carbohydrate is best achieved among respondents from higher social positions. The positive relation observed with healthy food intake and increasing education level was also present in macronutrient intake and a clear gender and social support interplay was seen in the nutrient intake levels.

Raw and Cooked Vegetables, Fruits, Selected Micronutrients, and Breast Cancer Risk: A Case-Control Study in Germany

In 1998-2000, a case-control study of breast cancer was conducted in Heidelberg, Germany. Three hundred ten consecutively recruited cases with primary breast cancer were matched according to 10-yr age groups to 353 controls with conditions unrelated to diet or endocrine disorders. Intake of raw vegetables, total vegetables, and whole-grain products was inversely associated with breast cancer risk (highest vs. lowest quartile adjusted odds ratio [OR] 0.51, 95% confidence interval [CI] 0.31-0.84; OR = 0.62, 95% CI = 0.38-1.02; and OR = 0.57; 95% CI = 0.34-0.95, respectively). Also, high intake of some selected vitamins and minerals possessing putative DNA-stabilizing properties displayed significant inverse risk associations. Adjusted ORs were as follows: vitamin C (OR = 0.49, 95% CI = 0.2-0.88), folate equivalents (OR = 0.47, 95% CI = 0.25-0.88), b-carotene (OR = 0.46, 95% CI = 0.27-0.80), zinc (OR = 0.35, 95% CI = 0.15-0.78), and copper (OR = 0.51, 95% CI = 0.31-1.03). In contrast, no significant association with risk was seen for an increased intake of fruits, cooked vegetables, fiber, calcium, manganese, or iron. In this population of German women, components of raw vegetables and some micronutrients appear to decrease breast cancer risk.

Nutrition and breast cancer risk by age 50: a population-based case-control study in Germany

Diet is recognized to play a role in the occurrence of breast cancer; however, the data are inconsistent. The goal of this study was to determine the influence of dietary factors on breast cancer risk among women up to 50 yr of age in a German population. A population-based case-control study was conducted including 706 cases and 1,381 controls. In addition to a risk factor questionnaire, a subgroup of 355 cases and 838 controls completed a food frequency questionnaire. Breast cancer risk was inversely associated with vegetable consumption (P for trend = 0.034). The odds ratio for the fourth quartile of vegetable intake compared with the first quartile was 0.64 (95% confidence interval = 0.43-0.96). Breast cancer risk increased with a higher consumption of red meat (P for trend = 0.016); women with the highest consumption level had an 85% elevated breast cancer risk compared with the lowest quartile (95% confidence interval = 1.23-2.78). When only premenopausal women were considered, the protective effect of vegetable intake and the positive association with meat intake were even stronger. These results are compatible with the international recommendations for a breast cancer preventive diet and suggest that the favorable effect of a diet high in vegetables and low in red meat, especially beef, may be stronger in premenopausal women.

Folate and breast cancer: the role of polymorphisms in methylenetetrahydrofolate reductase (MTHFR)

Evidence is growing that low folate status may be a factor in the aetiology of several cancers, including breast cancer. The methylenetetrahydrofolate reductase gene (MTHFR), which has a key role in folate metabolism, is polymorphic. We report a case-control study of two functional polymorphisms in MTHFR, dietary folate intake and breast cancer. Sixty-two cases with invasive breast cancer and sixty-six general practice controls participated. Women reporting the highest dietary folate intake had non-significantly reduced breast cancer risk (odds ratio (OR) = 0.49, 95% confidence interval (CI) 0.20-1.20). Risk was significantly lower for the 1298CC genotype compared to AA (OR = 0.24, 95% CI 0.06-0.97). Relative to compound wild-type subjects, compound heterozygotes had moderately reduced risk (OR = 0.47, 95% CI 0.11-1.92) and homozygote variants (677TT and/or 1298CC) greater reduced risk (OR = 0.26, 95% CI 0.07-0.96); the trend was statistically significant. Patterns in risk with regard to genotype and folate combinations are broadly similar those reported for colorectal neoplasia. The roles of MTHFR and folate in breast cancer aetiology are likely to be complex.

Curcumin exerts multiple suppressive effects on human breast carcinoma cells

In our study, we present experimental evidence suggesting that curcumin exerts multiple different suppressive effects on human breast carcinoma cells in vitro. Our experiments demonstrate that curcumin's antiproliferative effects are estrogen dependent in ER (estrogen receptor)-positive MCF-7 cells, being more pronounced in estrogen-containing media and in the presence of exogenous 17-beta estradiol. Curcumin inhibits the expression of ER downstream genes including pS2 and TGF-beta (transforming growth factor) in ER-positive MCF-7 cells, and this inhibition is also dependent on the presence of estrogen. Curcumin also decreases ERE (estrogen responsive element)-CAT activities induced by 17-beta estradiol. In addition, we demonstrate that curcumin exerts strong anti-invasive effects in vitro that are not estrogen dependent in the ER-negative MDA-MB-231 breast cancer cells. These anti-invasive effects appear to be mediated through the downregulation of MMP-2 (matrix metalloproteinase) and the upregulation of TIMP-1 (tissue inhibitor of metalloproteinase), 2 common effector molecules that have been implicated in regulating tumor cell invasion. Our study also demonstrates that curcumin inhibits the transcript levels of 2 major angiogenesis factors VEGF (vascular endothelial growth factor) and b-FGF (basic fibroblast growth factor) mainly in ER-negative MDA-MB-231 cells.