Dietary factors protective against breast cancer in Japanese premenopausal and postmenopausal women

Associations between soy, diet, reproductive factors, and mammographic density in Singapore Chinese women

Although the evidence is not completely consistent, soy intake has been inversely associated with breast cancer risk, and the strongest results have been observed in certain Asian populations. To address this issue and to examine the association between mammographic density and reproductive factors in this population, we conducted a cross-sectional analysis of mammograms and validated food-frequency questionnaires from 380 Chinese women living in Singapore. Percent mammographic density, a biomarker for breast cancer risk, was assessed using a validated computer-assisted method. We used generalized linear models to estimate mean mammographic density by quartiles of soy intake and intake of other dietary factors while adjusting for potential confounders. Percent mammographic density was inversely associated with age, body mass index, parity, breastfeeding, and soy intake. The difference in mammographic density between the highest and lowest quartiles of soy intake was 4-5%; this difference was statistically significant for soy protein and soy isoflavone intake and is similar in magnitude to what has been reported in Western populations when women undergo menopause or commence hormone therapy. We found no evidence that high fiber, fruit, or vegetable intake has protective effects on mammographic density. Our results suggest that the effect of soy intake on percent mammographic density is moderate but possibly of clinical relevance.

Breast cancer risk and erythrocyte compositions of n-3 highly unsaturated fatty acids in Japanese

Dietary intake of fish rich in n-3 highly unsaturated fatty acids (HUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), has been proposed to decrease cancer risk. In contrast to results from laboratory studies, however, protective effects for breast cancer have proved equivocal in epidemiological studies. In the present case-control study, we examined associations between breast cancer risk and fatty acid compositions in erythrocyte membranes as biomarkers for those intakes. Dietary information and blood samples were collected from 103 incident breast cancer cases and 309 non-cancer controls (matched by age and season) and erythrocyte fatty acids were measured using accelerated solvent extraction and gas-liquid chromatography. Dietary intake of n-3 HUFAs demonstrated a negative association with risk (the highest to the lowest tertile, odds ratio (OR), 0.51; 95% confidence interval (CI), 0.27-0.98; p(trend)<0.05), but there was no association with those of saturated fatty acids (SFAs) and meat. Moreover, risk was inversely associated with erythrocyte compositions of EPA (OR, 0.27; 95% CI, 0.14-0.53; p(trend)<0.0001), DHA (OR, 0.06; 95% CI, 0.02-0.16; p(trend)<0.0001) and n-3 HUFAs (OR, 0.11; 95% CI, 0.05-0.24; p(trend)<0.0001), and positively with that of SFAs (OR, 12.29; 95% CI, 4.94-30.57; p(trend)<0.0001) and the ratio of SFAs/n-3 HUFAs (OR, 14.65; 95% CI, 5.67-37.82; p(trend)<0.0001). In conclusion, we showed that erythrocyte compositions of specific fatty acids derived from fish intake, as biomarkers, are associated with lower risk of breast cancer, but further studies are needed to investigate mechanisms linked to the etiology.

Fish consumption and breast cancer risk. The European Prospective Investigation into Cancer and Nutrition (EPIC)

There is current interest in fish consumption and marine omega-3 (n-3) fatty acids and breast cancer risk. Some in vitro and animal studies have suggested an inhibitory effect of marine n-3 fatty acids on breast cancer growth, but the results from epidemiological studies that have examined the association between fish consumption and breast cancer risk in humans are inconsistent. We examined fish consumption and breast cancer risk in 310,671 women aged between 25 and 70 yr at recruitment into the European Prospective Investigation Into Cancer and Nutrition (EPIC). The participants completed a dietary questionnaire between 1992-98 and were followed up for incidence of breast cancer for a median of 6.4 yr. Hazard ratio for breast cancer by intake of total and lean and fatty fish were estimated, stratified by study centre and adjusted for established breast cancer risk factors. During follow-up, 4,776 invasive incident breast cancers were reported. No significant associations between intake of total fish and breast cancer risk were observed, hazard ratio (HR) 1.01 (95% confidence interval [CI] 0.99-1.02; p = 0.28 per 10 g fish/day). When examining lean and fatty fish separately, we found a positive significant association only in the highest quintile for fatty fish (HR 1.13, 95% CI 1.01-1.26), but test for trend was not significant (p = 0.10). No associations with breast cancer risk were observed when the study participants were subdivided by menopausal status. Although the period of follow-up is relatively short, the results provide no evidence for an association between fish intake and breast cancer risk.

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.

Dairy Product Consumption and the Risk of Breast Cancer

It has been suggested in some reports that dairy product consumption may increase the risk of breast cancer. This review gives a brief overview of the etiology of breast cancer and in particular the roles of fat, bovine growth hormone, insulin-like growth factor-1 and estrogens. Evidence from animal studies and epidemiology does not support a role for fat in the etiology of breast cancer. The daily intake of insulin-like growth factor-1 and biologically active estrogens from dairy products is minute in comparison to the daily endogenous secretion of these factors in women, whereas bovine growth hormone is biologically inactive in humans. On the other hand, milk contains rumenic acid, vaccenic acid, branched chain fatty acids, butyric acid, cysteine-rich whey proteins, calcium and vitamin D; components, which have the potential to help prevent breast cancer. Evidence from more than 40 case-control studies and 12 cohort studies does not support an association between dairy product consumption and the risk of breast cancer.

Intake frequency of fish and serum levels of long-chain n-3 fatty acids: a cross-sectional study within the Japan Collaborative Cohort Study

BACKGROUND: Several investigations have adopted self-reported intake frequency of fish as a surrogate for intake of long-chain n-3 fatty acids, for which protective effects against cancer have been suggested. Whether reported fish consumption reflects the fatty acid intake, however, has to be elucidated.

METHODS: We examined the association between intake frequency of fish and serum long-chain n-3 fatty acids (weight percentage of total fatty acids) among 1,257 control subjects (631 men and 626 women), aged 40-79 years, in case-control studies nested in the Japan Collaborative Cohort Study. All the subjects were not fasting when blood was drawn. Serum fatty acids were determined by gas chromatography.

RESULTS: In men, intake frequency of fresh fish and dried or salted fish was significantly but weakly correlated with serum levels of eicosapentaenoic (EPA), docosapentaenoic (n-3) (DPA), and docosahexaenoic (DHA) acids; the age-adjusted Spearman correlation coefficients ranged from 0.11 to 0.18. In women, fresh fish consumption was somewhat associated with serum EPA (Spearman correlation coefficient = 0.12) as was dried or salted fish consumption with serum DPA (0.11). A rising trend in geometric means of serum EPA, DPA, and DHA was found with an increasing intake frequency of fresh or dried/salted fish in both sexes. The geometric means adjusted for age and participating institution in the highest intake category were higher than those in the lowest by 7% to 40%.

CONCLUSIONS: A population with high self-reported frequency of fish intake, as a group, may have higher bioavailability of long-chain n-3 fatty acids than one with low frequency.

Dietary intakes of fat and fatty acids and risk of breast cancer: a prospective study in Japan

To examine the possible association of dietary fat and fatty acids with breast cancer risk in a population with a low total fat intake and a high consumption of fish, we analyzed data from the Japan Collaborative Cohort (JACC) Study. From 1988 to 1990, 26 291 women aged 40-79 years completed a questionnaire on dietary and other factors. Intakes of fat or fatty acids were estimated by using a food frequency questionnaire. Rate ratios (RR) were computed by fitting proportional hazards models. During the mean follow-up of 7.6 years, 129 breast cancer cases were documented. We found no clear association of total fat intake with breast cancer risk; the multivariate-adjusted RR across quartiles were 1.00, 1.29, 0.95, and 0.80 (95% confidence interval [CI] 0.46-1.38). A significant decrease in the risk was detected for the highest quartile of intake compared with the lowest for fish fat and long-chain n-3 fatty acids; the RR were 0.56 (95% CI 0.33-0.94) and 0.50 (0.30-0.85), respectively. A decreasing trend in risk was also suggested with an increasing intake of saturated fatty acids (trend P = 0.066). Among postmenopausal women at baseline, the highest quartile of vegetable fat intake was associated with a 2.08-fold increase in risk (95% CI 1.05-4.13). This prospective study did not support any increase in the risk of breast cancer associated with total or saturated fat intake, but it suggested the protective effects of the long-chain n-3 fatty acids that are abundant in fish.

Caloric restriction and calcium's effect on bone metabolism and body composition in overweight and obese premenopausal women

Obesity results in numerous preventable deaths and comorbidities. Unfortunately, a reduction of body weight has been correlated with a reduction in bone mass, the reasons for which have not been fully elucidated. The importance of maximizing peak bone mass during premenopausal years is well known. Most studies demonstrate a positive relationship between calcium intake and bone mass. However, during caloric restriction, which is commonly used for weight loss, calcium intake has shown mixed results. Calcium from dairy sources has received additional attention, beyond its importance to bone, for its role in regulating body weight and composition. Dairy foods are perceived as high fat, and therefore, are generally minimized or avoided during caloric restriction. The current calcium intake for premenopausal women is significantly below recommendations, and even if met during caloric restriction, may not be adequate. This review underscores the need for maintaining at least adequate intake levels of calcium, if not more, during weight loss regimens to minimize potential long-term detrimental effects on bone metabolism.

Common risk factors of breast and ovarian cancer: recent view

Clinicians, epidemiologists, and public health specialists tend to examine breast and ovarian cancer separately. Although this seems fairly rational and expected, both malignancies are estrogen related and thus share many risk factors. In this review, we investigate the common familial, reproductive, anthropometric, nutritional, and lifestyle risk factors of breast and ovarian cancer. We believe that the parallel examination of the two cancer types could significantly contribute to an improved prevention of "gynecological cancer" as a whole.

Long-chain (n-3) fatty acid intake and risk of cancers of the breast and the prostate: recent epidemiological studies, biological mechanisms, and directions for future research

The association between dietary (n-3) fatty acids and hormone-responsive cancers continues to attract considerable attention in epidemiological, clinical, and experimental studies. We previously reviewed the epidemiological literature on the association between hormone-responsive cancers and the long-chain fatty acids eicosapentaenoic acid and docosahexaenoic acid. We concluded that the compelling evidence from ecological studies, animal models, and mechanistic experiments in vitro was not supported clearly by the available epidemiological data. To various degrees, epidemiological studies published more recently attempted to address some of the methodological limitations plaguing earlier studies by using validated questionnaires, examining specific fatty acids and their interrelationships, and adjusting estimates for a wider range of potentially confounding factors than in previous studies. In this review, our aim was to update the previous review with the results of recent epidemiological studies and to discuss possible biological mechanisms and directions for future research.