Nutritional and Lifestyle Risk Factors for Breast Cancer Among Malaysian Women: A Case-Control Study

Breast cancer is the most common incident cancer in women worldwide, accounting for 9% of all new cancers. While the exact causes of breast cancer are unknown, the risks are higher among older women (50 years and above) than those less than 35 years. Dietary factors that have been linked to breast cancer include saturated fat, meat, vegetables and fruits. Other factors that have been linked to breast cancer include age at menarche, age at first and last birth, smoking, use of oral contraceptives and body mass index. This case-control study was carried out to determine the nutritional and lifestyle risk factors of breast cancer among Malaysian women. A total of 162 pre- and post-menopausal women (81 cases and 81 controls) was included in the study, which was carried out between 1 January to 31 December, 2000. Cases were selected frorrf the Breast Cancer Clinics in Hospital Kuala Lumpur (HKL) and Universiti Malaya Medical Centre (UMMC). All cases were newly diagnosed and have not undergone any treatment or surgery. Controls were women staff and wives of staff of Universiti Putra Malaysia (UPM). They were matched by age (+ 5 years) and ethnicity with the cases. Additional Chinese controls (17 women) were selected from the Malaysian-Chinese Association (MCA) from Ampang Jaya by invitation to the group's leader. Data collection was carried out in four main parts: the interview (to obtain socio-demographic and lifestyle data); anthropometric measurements; dietary information, using semi-quantitative food frequency questionnaire; and biochemical data (to obtain serum lipid profile). Majority of the respondents were pre-menopausal women with the mean age of 46.63 in cases and 47.58 in controls. Half of the breast cancer patients were seen at UMMC while the other half in HKL, and most of them (43.1%) presented with a second stage of cancer. Smoking, exercise, breast-self examination and breastfeeding practices were not significantly different between the two study groups. However, there was a significant difference in the duration of exercise between cases and controls. Reproductive history like age at menarche, age at first marriage, age at first birth and parity. were also not significantly different between cases and controls. Anthropometric indicators like height, weight, waist and hip measurements, a s well a s body m ass i ndex a nd w aist-hip ratio d id n ot show any association with breast cancer, and neither were they significantly different between case and control subjects. Intakes of micronutrient were not significantly different between the two study groups with the exception of sodium. Blood lipid profiles also did not show any difference between groups. Preliminary data showed that women who 3 have four to five children were 1.32 times more at risk for breast cancer as compared to those who never had any children (95% CI=1.32-1.47). Multiple logistic regression model showed that menarche at higher age and increased BMI decreased breast cancer risk while higher age at last birth increased breast cancer risk. The relatively small sample size of this study could have resulted in this results. Furthermore, there could have been recall bias and under-reporting of energy intake among case subjects due to the occurrence of the disease. Larger cohort and interventional studies should be carried out to further explore this factors with relation to breast cancer.

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