Japanese Journal of Clinical Oncology Advance Access published online on August 18, 2007
Japanese Journal of Clinical Oncology, doi:10.1093/jjco/hym062
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© 2007 Foundation for Promotion of Cancer Research
Alcohol Drinking and Breast Cancer Risk: An Evaluation Based on a Systematic Review of Epidemiologic Evidence among the Japanese Population
1 Department of Epidemiology and Preventive Medicine, Gifu University Graduate School of Medicine, Gifu
2 Department of Epidemiology and International Health, Research Institute, International Medical Center of Japan, Tokyo
3 Department of Preventive Medicine, Saga Medical School, Faculty of Medicine, Saga University, Saga
4 Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai
5 Department of Preventive Medicine/Biostatistics and Medical Decision Making, Nagoya University Graduate School of Medicine, Nagoya
6 Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan
For reprints and all correspondence: Chisato Nagata, Department of Epidemiology and Preventive Medicine, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu 501-1194, Japan. E-mail: chisato{at}gifu-u.ac.jp
Received December 22, 2006; accepted March 10, 2007
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Abstract |
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Background: We reviewed epidemiological studies on alcohol drinking and breast cancer among the Japanese population. This report is one among a series of articles by our research group evaluating the existing evidence concerning the association between health-related lifestyles and cancer.
Methods: Original data were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database, complemented with manual searches. Evaluation of associations was based on the strength of evidence and the magnitude of association, together with biological plausibility as previously evaluated by the International Agency for Research on Cancer.
Results: Three cohort studies and eight case-control studies were identified. There were inconsistent results regarding alcohol drinking and breast cancer risk among cohort studies. A significant positive association was observed in one, but another showed nonsignificant inverse association. Out of the eight case-control studies, two studies showed a significantly increased risk among women who drink daily and who had higher intake of alcohol, respectively. Experimental studies have supported the biological plausibility of a positive association between alcohol drinking and breast cancer risk.
Conclusion: We conclude that epidemiologic evidence on the association between alcohol drinking and breast cancer risk remains insufficient in terms of both the number and methodological quality of studies among the Japanese population.
Key Words: systematic review • epidemiology • alcohol drinking • breast cancer • Japanese
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INTRODUCTION |
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TOPAbstractINTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...AppendixReferences |
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Many epidemiologic studies have identified chronic alcohol consumption as a risk factor for breast cancer. Previous meta-analyses have shown a positive association between alcohol intake and breast cancer (1–9). However, most of the component studies have been conducted among western populations. We reviewed epidemiological studies on alcohol drinking and breast cancer among the Japanese population. This report is one among a series of articles by our research group, investigating the associations between lifestyles and major types of cancer in Japan.
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METHODS |
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A MEDLINE search was conducted to identify epidemiological studies on the association between alcohol drinking and breast cancer incidence or mortality among Japanese from 1980 to 2006. A search of the Ichushi (Japana Centra Revuo Medicina) database was also done to identify the studies written in Japanese from 1983 to 2006. Papers written in either English or Japanese were reviewed, and only studies on Japanese populations living in Japan were included.
Individual results were summarized in the tables separately by study design as cohort or case-control studies. Relative risks (RRs) or odds ratios (ORs) in each epidemiologic study were grouped by magnitude of association, with consideration to statistical significance (SS) or no statistical significance (NS), as strong, <0.5 or >2.0 (SS); moderate, either (i) <0.5 or >2.0 (NS), (ii) >1.5–2 (SS), or (iii) 0.5 to <0.67 (SS); weak, either (i) >1.5–2 (NS), (ii) 0.5 to <0.67 (NS) or (iii) 0.67–1.5 (SS); or no association, 0.67–1.5 (NS). After this process, the strength of evidence was evaluated in a similar manner to that used in the WHO/FAO Expert Consultation Report (10), in which evidence was classified as ‘convincing’, ‘probable’, ‘possible’ and ‘insufficient’. We assumed that biological plausibility corresponded to the judgment of the most recent evaluation from the International Agency for Research on Cancer (IARC) (11). In the case of multiple publications of analyses of the same or overlapping datasets, only data from the largest or most updated results were included, and incidence was given priority over mortality as an outcome measure. Details on the evaluation methods are described elsewhere (12).
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MAIN FEATURES AND COMMENTS |
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We identified three cohort studies (13–15) and eight case-control studies (16–23). Tables 1 and 2 give details of the component studies including age range, study period, numbers of women enrolled, RR or OR of breast cancer for alcohol drinking and covariates used in adjustment. Studies that presented separate estimates of RR or OR were subdivided by drinking status, frequency of alcohol drinking, alcohol consumption, type of alcohol, or/and menopausal status.
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Summaries of the magnitudes of association for these studies are shown in Tables 3 and 4.
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There was an inconsistency of results among the cohort studies. A significantly increased risk was observed in women with high intake of alcohol (
15 g/day) in one study (15). Decreased risk among daily drinkers was reported in one of the remaining cohort studies, although this association was not statistically significant (13). Among case-control studies, a significantly increased risk among daily drinkers (OR = 1.35) as compared with others was reported in the study by Kato et al. (16). A significantly increased risk (OR = 2.03) was observed among pre-menopausal women with high intake of alcohol (1 go/day) (1 go is about 23 g of alcohol) as compared with non-drinkers in the study by Hirose et al. (20). These two studies were conducted in the same institute, but the study time was not overlapped. A significantly decreased risk was reported in one study (17). The other studies found no significant associations between breast cancer risk and any of variables related to alcohol drinking.
Unlike the previous reviews of studies, the evidence for the link between alcohol drinking and breast cancer risk was weak in the present reviews of Japanese studies. However, considering the modest strength of the association between alcohol drinking and breast cancer, reports of no significant association are not surprising. The result from a recent meta-analysis including 98 studies involving 75 728 cases revealed that excess risk associated with drinking was 22% for studies judged high quality (10). Two case-control studies (19,21) in the present review reported higher risk estimates for drinkers as compared non-drinkers, although the associations were not statistically significant. The meta-analysis also showed that the risk of breast cancer increased by 10% for each additional 10 g per day intake of alcohol. Lack of information concerning alcohol consumption in most of the studies in the present review precluded us from evaluating the dose–response relationship. It also makes it difficult to estimate the average amount of alcohol. Japanese female drinkers may consume less alcohol than female drinkers in other countries previously studied, which may have lead to the lack of significant association. In fact, the percentage of heavy drinkers seems very low in Japanese women. In a cohort study reported by Lin et al., the percentage of women who had 15 g or more of alcohol per day was 2.7% (15). The percentage of women who had 1 go or more per day was 1.4% in a case-control study reported by Hirose et al. (20). However, the corresponding figures were 12.4 and 6.2%, respectively, in the previous review of 53 studies in the world (8). We also referred to general population data from other sources. According to the Japan Public Health Center-based Prospective Study in Japan, the percentage of women who had 150 g or more of alcohol per week was 2.6% (24). In the third National Health and Nutrition Examination Survey (25) in the USA, the percentages of light (0.1–6.4 g/day), moderate (6.5–25.9 g/day) and heavy (26 g/day) drinkers were 27.0, 12.9 and 2.8%, respectively. It is also possible that infrequent drinkers or ex-drinkers may have reported that they were non-drinkers. Such a bias may have led to underestimation of the association.
Our previous review of Japanese studies regarding smoking and breast cancer suggested that smoking possibly increases the risk of breast cancer among Japanese women (26). Therefore, there is a potential for smoking confounding the results of the association between alcohol drinking and breast cancer. Three studies (15,17,23) provided the risk estimates after adjusting for smoking. The authors did not observe a confounding effect of smoking. Most of the other studies stated that information on smoking was obtained. It is unlikely that the observed lack of association in these studies is due to the confounding effects of smoking.
Results from experimental studies in animals have shown that ethanol intake can cause mammary tumor genesis (11). Several potential mechanisms have been also provided for potential indirect effects of alcohol, such as perturbation of estrogen metabolism and response, as well as by an effect on one carbon metabolism pathway, through reduced folic acid intake and use (27). Thus, it is biologically plausible that alcohol drinking is related to breast cancer.
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EVALUATION OF EVIDENCE ON ALCOHOL DRINKING AND BREAST CANCER RISK IN JAPANESE |
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From these results, we conclude that epidemiologic evidence on the association between alcohol drinking and breast cancer risk remains insufficient in terms of both the number and methodological quality of studies among the Japanese population. Based on epidemiologic studies in the world and assumed biological plausibility, some evaluations conclude that alcohol drinking increases the risk of breast cancer. Therefore, more epidemiologic studies with large samples, including sufficient number of drinkers and with more accurate methods for estimating alcohol intake, are needed in Japan to clarify the risk associated with alcohol drinking and to identify the high risk group.
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Appendix |
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Research group members: Shoichiro Tsugane [Principal Investigator], Manami Inoue, Shizuka Sasazuki, Motoki Iwasaki, Tetsuya Otani (National Cancer Center, Tokyo); Ichiro Tsuji [since 2004], Yoshitaka Tsubono [in 2003], Taichi Shimazu (Tohoku University, Sendai); Yoshikazu Nishino (Miyagi Cancer Research Institute, Natori, Miyagi); Kenji Wakai (Nagoya University, Nagoya); Chisato Nagata (Gifu University, Gifu); Tetsuya Mizoue (International Medical Center of Japan, Tokyo); Keitaro Tanaka (Saga University, Saga).
Conflict of interest statement
None declared.
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Acknowledgments |
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The authors gratefully acknowledge the assistance of Ms Izumi Suenaga and Mr Ryuta Abe. This work was supported by the Third Term Comprehensive 10-year Strategy for Cancer Control from the Ministry of Health, Labour and Welfare, Japan.
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References |
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