1 Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA.
2 Department of Epidemiology, Zhong Shan Hospital Cancer Center, Shanghai, China.
3 Department of Epidemiology, University of Washington, Seattle, WA.
4 Shi Dong Hospital, Shanghai, China.
5 Veterans Administration Medical Center, Portland, OR.
6 Institute of Medical Biology, University of Tromsø, Tromsø, Norway.
7 Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC.
Received for publication December 16, 2003; accepted for publication June 10, 2004.
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ABSTRACT |
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breast diseases; diet; estrogens; fibrocystic disease of breast; fruit; risk factors; soy foods; vegetables
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INTRODUCTION |
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Previous studies have shown increased risk of fibrocystic breast conditions in the aggregate to be associated with high social class (3, 4, 7, 8), late age at menopause (3, 4, 6, 8, 9), estrogen replacement therapy (3), nulliparity (3, 4, 6, 810), low body mass index (3, 4, 7, 8, 11), and family history of breast cancer (4, 69, 12), while high parity (3, 79), oral contraceptive use (3, 4, 6, 7, 10, 13), and physical activity (14, 15) have been related to decreased risk. Most reports have shown no substantial effect of ever, former, or current smoking on development of fibrocystic conditions, even across different grades of atypia (3, 6, 8). Results have been inconsistent for young age at first full-term pregnancy (3, 7, 9, 16) and lactation (7). Age at menarche has not been associated with risk (3, 4, 10).
Among the dietary factors studied, the most consistent finding is an apparently protective effect of fruits and vegetables (1720). Diets high in fiber (2123) and soy products (21) have also been associated with reduced risk, but a randomized trial showed increased cell division in lobular mammary epithelium after soy protein supplementation (24). Consumption of green vegetables has been inversely associated specifically with risk of proliferative benign breast disease (20). Results from studies of total fat are inconsistent (3, 19, 25, 26). In one study, high daily intake of energy was reported to be positively associated with benign epithelial cell proliferative disease (22).
We conducted this study to evaluate the role that reproductive and dietary factors, particularly antioxidants and certain phytoestrogens, may play in the development of mammary epithelial cell proliferation in Chinese women with fibrocystic breast conditions.
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MATERIALS AND METHODS |
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A total of 622 women with fibrocystic breast conditions were identified for this study, and in-person interviews were completed for 551 (89 percent) of them. Of these women, 389 (71 percent) had satisfactory slides for review (at least five scanning power fields) and were included in the analyses for this report.
Women whose breast conditions were diagnosed between September 1995 and August 1997 were simultaneously enrolled in an ongoing immunocytochemical study of mammary cell proliferation (unpublished data). Controls for the present study were selected from unaffected women in the breast self-examination trial cohort. For each benign and malignant case also enrolled in the previous study of cell proliferation, 20 potential controls of the same age were randomly selected. Women were contacted, starting with the first two names on the list, until two women of the same age and menstrual status as their matched case were recruited. All 367 controls recruited in this manner (64 percent of the eligible women contacted) were included in the analyses for this report. Controls for the cases who were not enrolled in the study of cell proliferation were frequency matched to cases eligible for this study, as well as to cases also eligible for two concurrent studies of breast cancer and fibroadenoma, by 5-year age group and hospital affiliation of their factories at baseline. In-person interviews were completed for 704 (82 percent) of 862 controls selected in this manner.
Data collection
A baseline questionnaire was administered orally to all women in the breast self-examination trial by factory medical clinic workers between October 1989 and October 1991. The women who participated in the present study were reinterviewed from 1995 through 2001 by members of a team of specially trained former medical clinic workers, utilizing a detailed general risk factor questionnaire and a food frequency questionnaire. Cases were interviewed in hospitals or clinics, usually at the time of their initial visit for their breast problem, before the histologic diagnosis was made. Controls were interviewed in their homes or factories. Information was elicited on demographic characteristics, reproductive and gynecologic history, smoking and alcohol habits, medical history, family history of breast cancer, and occupational and recreational physical activities. Because prior breast surgery reported by many women erroneously included the surgery conducted for the present disease, information from the baseline questionnaire on prior breast surgery was utilized. The food frequency questionnaire was based on a previously validated instrument (29, 30) and ascertained data on the frequency of intake of 99 food items during adult life. Respondents provided information on their usual frequency of intake (per day, week, month, or year) of each item. The seasonality of fruit and vegetable consumption was accounted for by asking subjects to report the number of months of the year in which they consumed each item.
Informed consent was obtained from each woman prior to interview. The study was approved by the institutional review boards of the Fred Hutchinson Cancer Research Center and the Station for Prevention and Treatment of Cancer of the Shanghai Textile Industry Bureau, in accordance with assurance filed with the Office for Human Research Protections of the US Department of Health and Human Services.
Validation of diagnosis and histologic classification
A single study pathologist (M. L.) read slides from all cases without knowledge of their original diagnosis. He recorded the number of scanning power fields examined and classified the womens conditions into three different types of fibrocystic breast conditions according to the scheme developed by Stalsberg (31). Cases with atypia were those with atypical ductal hyperplasia, atypical lobular hyperplasia, or moderate apocrine atypia (33 cases). Cases with proliferative changes were those with moderate or florid ductal hyperplasia or moderate or predominant sclerosing adenosis and no atypia (181 cases). Subjects with mild or no ductal hyperplasia and subjects with mild or no sclerosing adenosis were classified as having nonproliferative fibrocystic breast conditions (175 cases).
Randomly selected slides from the three major groups of fibrocystic breast conditions were read by a reference pathologist (H. S.). There was a satisfactory level of agreement between the readings made by the study pathologist and the reference pathologist on the presence or absence of proliferation and atypia (weighted = 0.4), and the benign conditions were categorized into 1) nonproliferative, 2) proliferative without atypia, and 3) proliferative with atypia for analysis. In all instances, the diagnoses made by the study pathologist were used.
Data analysis
All individual food consumption frequencies were converted to annual frequencies. Intake of fruits and vegetables was computed by weighting the frequency of intake by the number of months per year during which the food item was eaten. The 99 foods were grouped into 19 mutually exclusive food groups (Appendix 1). The individual annual frequencies of intake for the foods in each group were summed to create values for consumption of the food group. Amounts of sesame and soybean oils consumed were estimated by dividing the amounts used by the womans family per day by the number of family members. Nine fried food items were combined into a separate high-fat group. Fruits and vegetables were further classified into mutually exclusive botanical families (Appendix 2). Total daily energy intake was calculated from all macronutrients, oils, and alcohol using 1991 Chinese food composition tables (32, 33) and estimated average serving sizes from the 1992 China Health and Nutrition Survey (34). Total daily dietary intakes of vitamin E (mg of -tocopherol equivalents), carotenoids (µg), vitamin C (mg), and crude fiber (g) were also calculated from the same Chinese food composition tables (32, 33). One woman with a nonproliferative fibrocystic breast condition and one control were excluded because their calculated daily energy intakes were considered implausible at more than 4,000 kcal.
To assess potential trends in risk with level of consumption, we divided food groups, botanical families, and nutrients into quartiles according to the distribution of consumption among the controls. We created fewer categories for food groups with too little variation in intake to create meaningful quartiles. Because controls were interviewed after the corresponding cases, they tended to have been interviewed at a later date. Therefore, we stratified study subjects by year of interview (19951996, 1997, 19981999, 20002001) in all analyses. We computed odds ratios (as estimates of relative risk) and associated 95 percent confidence intervals using conditional logistic regression (35). For small sample sizes (<5), we used exact logistic regression to calculate odds ratios and confidence intervals. All odds ratios were adjusted for age using 5-year age categories. We assessed residual confounding by age by comparing selected results in these analyses with results of analyses in which age was modeled as a continuous variable; no residual confounding by age was detected. The odds ratios for food groups were further adjusted for total energy intake (36). Odds ratios for botanical groups and specific micronutrients were adjusted for age and total fruit and vegetable intake. We performed tests for trend by entering the categorical variables in regression models as ordinal variables. We evaluated potential confounding by adding variables independently to the appropriate model. Variables were considered as confounders if they changed the estimated ß coefficient of the main independent variable by 10 percent or more.
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RESULTS |
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With the possible exception of atypia, no associations with red meat were observed. Unexpectedly, there were decreasing trends in risk of nonproliferative conditions with increasing intakes of cured meat and fish and fried foods. With these two exceptions, no associations were observed with fish, cured meat and fish, poultry, eggs, shellfish, sesame oil, soybean oil, fried foods, rice, or tea.
The significant odds ratios shown in table 3 were adjusted further for other food groups and for age at first livebirth, parity, family history of breast cancer, physical activity during the womans 20s40s, intrauterine device use, oral contraceptive use, a prior breast lump, active and passive smoking, body mass index, and frequency of breast self-examination. Adjustment for any of these variables did not significantly alter the odds ratios for any of the food groups, nor did adjustment for these dietary factors appreciably alter the odds ratios in relation to any of the nondietary factors shown in table 2.
Table 4 shows odds ratios in relation to intake of mutually exclusive botanical groups, adjusted for age and total intake of fruits and vegetables. The Compositae, Rutaceae, Sapindaceae, and Vitaceae families were significantly associated with reduced risk of nonproliferative fibrocystic breast conditions. The Sapindaceae and Vitaceae families were similarly associated with proliferative fibrocystic breast conditions. Possible associations of Compositae and Rutaceae with proliferative fibrocystic breast conditions were not as strong as those with nonproliferative fibrocystic breast conditions and were not statistically significant. The Zingiberaceae family was significantly associated with increased risk of proliferative conditions and atypia. The Umbelliferae family was possibly associated with increased risk of all three histologic types of fibrocystic breast conditions, but the trends were not statistically significant.
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DISCUSSION |
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Because of the focal distribution of fibrocystic conditions in the breast, there was probably some misclassification of the lesions into the three histologic types. This would have tended to obscure true differences in odds ratios for the three histologic types, and observed differences in odds ratios may reflect larger actual differences.
Decreasing trends in risk with increasing numbers of livebirths were stronger for atypia and proliferative conditions than for nonproliferative conditions, suggesting that high parity may protect against breast cancer by reducing mammary epithelial cell proliferation and atypical changes. A similar interpretation could be argued for the effect of age at menarche on risk, but the differences in the odds ratios among the three groups in relation to this factor were less striking than those for parity and could readily have been due to chance.
Smoking is known to reduce endogenous estrogen levels, and the weak decreasing trend in risk of proliferative (but not nonproliferative) conditions with years of having lived with a spouse who smoked suggests that environmental tobacco smoke could reduce cell proliferation in the mammary epithelium through its effect on estrogen levels. However, this observation could also be due to chance.
A history of benign breast lesions was associated with increased risk of fibrocystic breast conditions. It was not possible to determine whether the prior lumps were fibrocystic breast conditions or other benign breast conditions, so risks related to specific types of benign breast conditions could not be estimated. However, multiple occurrence and recurrence of fibrocystic breast conditions has been well established (2, 3). Our findings suggest that this phenomenon may be more common for proliferative conditions than for nonproliferative conditions.
Previous studies have found a positive family history of breast cancer or benign breast disease to be related to fibrocystic breast conditions (4, 69, 12). In this study, after adjustment for multiple variables, family history of breast cancer was no more strongly associated with proliferative fibrocystic breast conditions than with nonproliferative fibrocystic breast conditions. However, few women reported a family history of breast cancer, and the power of this study to distinguish differences in risk in relation to this factor was low.
The increased relative risks associated with history of breast self-examination clearly indicate increased detection of fibrocystic breast conditions among women who practice breast self-examination. If breast self-examination were associated with any of the other factors considered, this confounding could explain observed relations of risk to these factors. However, no confounding by breast self-examination practice was observed.
The main finding from this study is that consumption of fruits and vegetables was associated with a reduced risk of all three types of fibrocystic breast conditions and that the associations were stronger for atypia and proliferative conditions than for nonproliferative conditions. Thus, it seems reasonable to conclude that fruits and vegetables contain substances that exert an antiproliferative or proapoptotic effect on the mammary epithelium. However, of the 16 botanical families considered individually, none was appreciably more strongly associated with proliferative conditions than with nonproliferative conditions after results were controlled for total fruit and vegetable intake. Similarly, specific micronutrients derived from fruits and vegetables (i.e., vitamins C and E and carotenoids) were also not associated with these conditions after controlling for total fruit and vegetable intake. These observations suggest that the apparent inhibitory effect of fruits and vegetables on the development of proliferative changes in the breast is not due to consumption of any single specific nutrient or food but rather is a result of total fruit and vegetable consumption or of following an overall dietary pattern rich in fruits and vegetables.
Vegetables and fruits are rich sources of a variety of nutrients, including vitamins, trace minerals, and fiber, and numerous bioactive and potentially anticarcinogenic compounds (3739). These phytochemicals can have complementary and overlapping potential mechanisms of action, including quenching free radicals and inhibiting DNA adduct formation, altering hormone and carcinogen metabolism, and directly affecting cell proliferation, differentiation, and apoptosis. If the net result of these effects were to enhance the ratio of the rate of cell proliferation to cell differentiation or death, proliferative changes would result.
Many in vitro and in vivo studies have provided experimental evidence for a protective effect of soy isoflavones against certain hormone-dependent cancers, including breast cancer (40). Case-control studies of soy food intake and risk of breast cancer in Asian women have yielded weak associations and inconsistent results (4143). Furthermore, one prospective study carried out in Japan showed no association between breast cancer risk and soy foods (44), which suggests that associations based on retrospectively collected data may be due to differential recall of intake by cases and controls. In the present study, decreasing trends in risk with increasing intake of soy foods were strongest for fibrocystic conditions with atypia, weaker for proliferative conditions without atypia, and absent for nonproliferative conditions. Although these differences could be due to chance, they are also consistent with the hypothesis that isoflavones in soy could reduce risk of breast cancer by inhibiting mammary epithelial cell proliferation. This effect would be exerted early in the carcinogenic process, which is consistent with results from two studies that show reduced risk of breast cancer to be associated particularly with soy intake during adolescence (42, 45). Possible mechanisms for this include a reduction in the level of endogenously produced estrogens in response to soy intake (46, 47) and competitive binding at estrogen receptor sites (37).
Some previous studies have found that saturated fats but not mono- or polyunsaturated fats are directly, although moderately, associated with breast cancer risk (3, 19, 25, 26). High-fat diets have been associated with higher circulating estrogen levels (21). However, we did not find any association between consumption of fried foods or percentage of energy derived from fat and risk of proliferative fibrocystic breast conditions. We did observe a possible association of atypia with consumption of red meat, which might suggest a role of animal fats in the development of atypical changes.
Other associations between specific food groups and botanical families and one or more of the three histologic categories of fibrocystic conditions were observed, but many possible relations were considered, and biologic interpretations are not warranted unless the observations are confirmed by others. The absence of associations with the Cruciferae does not support the a-priori hypothesis that substances in these foods can protect against breast diseases.
One limitation of this study is that almost 30 percent of the cases had breast lesions that could not be classified because insufficient material was available for review. However, these women did not differ significantly from those included in the analyses by age, parity, body mass index, total energy intake, or fruit or vegetable consumption (data not shown), so the exclusion of these cases is unlikely to have influenced the results.
Another limitation of this study is that average serving size was used to calculate intake for all food groups. This could have resulted in imprecise estimates of intake but would only have biased odds ratio estimates toward the null. This effect is probably small because most variability in food consumption is due to frequency of intake, not portion size (36).
Although our food frequency questionnaire was not validated for intake of all foods, Frankenfeld et al. (48) compared soy intake estimated from the food frequency questionnaire and Chinese food tables to isoflavone concentration in plasma samples collected within 1 week of food frequency questionnaire completion. A significant linear trend was observed in serum daidzein and genistein concentrations across increasing categories of soy intake. These results suggest that the food frequency questionnaire provided a reasonably good assessment of soy food consumption.
A strength of this study is the variety in and wide range of consumption of fruits and vegetables in the study population, which enhanced our chances of discovering variations in risk with consumption levels. Another strength is the standardized histologic classification of fibrocystic breast conditions by a single pathologist. The final histologic classification of each case was based on the most advanced change in any of the scanning power fields reviewed. Therefore, the chance of recording high scores might be associated with the number of scanning power fields examined, and, if this was associated with a variable of interest, a spurious association with that variable could have resulted. However, the numbers of scanning power fields examined were similar for the three histologic types of fibrocystic breast conditions (data not shown), providing evidence that a high score was not a function of the number of fields examined.
In summary, a diet rich in fruits and vegetables was associated with a reduced risk of proliferative fibrocystic breast conditions. Reduction of mammary epithelial cell proliferative changes may be one mechanism by which fruits and vegetables reduce risk of breast cancer.
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ACKNOWLEDGMENTS |
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The authors thank Wenwan Wang and the medical workers, breast self-examination workers, and interviewers of the Shanghai Textile Industry Bureau for their efforts in collecting data; Drs. Fan Liang Chen, Guan Lin Zhao, and Lei Da Pan for their support of all of the studies carried out in Shanghai; and Judith Calman, Georgia Green, Ted Grichuhin, Jan Kikuchi, Mary Molyneaux, Karen Wernli, and Shirley Zhang for their technical and administrative assistance.
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APPENDIX 1 |
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Foods Assessed within Each Food Group, Shanghai Nutrition and Breast Disease Study, 19952000
Fruits
Apples
Pears
Oranges or tangerines
Litchis
Bananas
Peaches
Persimmons
Pineapples
Grapes
Apricots
Watermelon
Vegetables
Bok choy
Spinach
Cabbage
Chinese cabbage
Watercress
Broccoli
Chinese broccoli
Green asparagus
Cauliflower
Celery
Eggplant
Wild rice stem
Winter squash
Lettuce
Yellow sweet potatoes or yams
Other potatoes
Wax gourd
Gherkin (cucumber)
Carrots
Pumpkin
Mushrooms
Red or green pepper
Tomato
Bamboo shoots
Radishes or turnips
Lotus rhizomes
Taro root
Corn
Onions and chives
Garlic stalk
Seaweed
Preserved vegetables
Salted mustard greens
Other salted vegetables
Soy foods
Soybeans
Soybean milk
Fried bean curd puff
Fresh bean curd
Other soybean foods
Fermented bean curd
Other legumes
Dried
Red pea or green bean soup
Peanuts
Peanut butter
Mung beans
Other dried beans
Fresh
Mung bean sprouts
String beans
Hyacinth beans
Peas or cowpeas
Green or kidney beans
Fresh fava beans
Red meat
Pork
Pork chops
Spareribs
Pig trotters
Fresh pork, fat and lean
Ham
Pork liver
Beef
Other red meat
Organ meat (except liver)
Lamb or mutton
Fish
Saltwater fish
Hair tail or yellow crooker
Freshwater fish
Carp
Rice-field or Japanese eel
Canned fish
Cured meat and fish
Chinese sausage
Salted pork
Salted fish
Poultry
Chicken
Duck or goose
Eggs
Shellfish
Shrimp
Crab
Snail
Conch
Squid
Sea cucumber
Oysters
Mussels
Clams
Dairy foods
Fresh whole milk
Fresh nonfat milk
Ice cream
Powdered milk
Rice
Other grains
Steamed bread, unfilled
Cakes or pastries
Cookies
Wheat gluten
Noodles
Sesame oil
Soybean oil
Fried foods
Fried bean curd puff
Fried chicken
Breaded fried vegetables
Breaded fried fish
Breaded fried pork chop
Deep-fried egg rolls
Deep-fried dumplings
Deep-fried dough sticks
Pan-fried pizza
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APPENDIX 2 |
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Foods Assessed within Each Botanical Family, Shanghai Nutrition and Breast Disease Study, 19952000
Araliaceae
Fresh ginseng
White ginseng powder or extract
Red ginseng powder or extract
Compositae
Sunflower seeds
Lettuce
Convolvulaceae/Dioscoreaceae
Yellow sweet potatoes
Yams
Cruciferae
Bok choy
Cabbage
Chinese cabbage
Watercress
Broccoli
Chinese broccoli
Cauliflower
Radishes or turnips
Cucurbitaceae
Winter squash
Wax gourd
Gherkin (cucumber)
Pumpkin
Watermelon
Laminariaceae
Seaweed
Leguminosae
Peanuts
Peanut butter
Soybean milk
Fried bean curd puff
Fresh bean curd
String beans
Soybeans
Mung beans
Green or kidney beans
Fresh fava beans
Hyacinth beans
Peas or cowpeas
Other dried beans
Mung bean sprouts
Red pea or green bean soup
Other soybean foods
Liliaceae
Asparagus
Garlic
Garlic stalk
Onions
Chives
Scallions
Chinese chives
Nymphaceae
Lotus rhizomes
Rosaceae
Apples
Pears
Peaches
Apricots
Rutaceae
Oranges
Tangerines
Sapindaceae
Litchis
Solanaceae
Eggplant
Other potato
Tomato
Hot pepper
Red or green pepper
Umbelliferae
Celery
Carrots
Vitaceae
Grapes
Zingiberaceae
Ginger root
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NOTES |
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REFERENCES |
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