Breast Cancer and nutrition in the Kilimanjaro Region of Northern Tanzania: a case-control study
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Breast cancer is the leading cause of death among women worldwide and the second most common cancer among women in the Kilimanjaro Region of Tanzania. Studies in industrialised countries identified age at menarche, age at first full-term pregnancy, and lactation as determining factors in the aetiology of breast cancer. Apart for alcohol, no scientific agreement could be found on whether specific nutrients or dietary patterns have an impact on breast cancer risk. At first, a food frequency questionnaire was validated. Secondly, a case-control study was conducted with a focus on dietary patterns and breast cancer. This was done based on the hypotheses that nutrients are ingested within diets rather than as single nutrients. In addition it was assumed that in a community with a low risk lifestyle and reproductive behaviour like in Tanzania it is more likely to detect linkages between dietary intake and breast cancer than in communities of high income countries.The FFQ was validated between July 2005 and February 2006. In absence of a gold standard the 24h-recall method was chosen as validation tool. The 24h-recall is known for being less sensitive for recall bias but has a high day to day variability. Two data assessments were conducted in different agricultural seasons. In the case-control study 115 female breast cancer patients (cases) and 230 age- and district-matched women clinically free from breast cancer (controls) were interviewed about their reproductive history and socioeconomic condition. Semi-structured interviews including anthropometric measurements were conducted by trained enumerators. The validated semi-quantitative Food Frequency Questionnaire was used to assess the dietary intake. A logistic regression was performed to estimate breast cancer risk. Dietary patterns were obtained using principal component analysis with Varimax rotation and added as additional predictors to the basic logistic model.The median age of the women in the case-control study was 50 years (min/max 26 to 85 years). Estimated median BMI at age 20 was 21kg/m² in both cases and controls. Median lifelong lactation of the mothers was 96 months (cases) and 108 months (controls). A high BMI at 20 years was associated with an increased breast cancer risk (OR 1.31 95 % CI 1.11-1.55, P <0.01). The odds ratio for lifelong lactation was slightly below one (OR 0.99 95 % CI 0.98-1.00, P < 0.01). There was no significant association in risk for BMI at interview (median 25 kg/m² of cases and 26 kg/m² of controls), age at menarche (median 16 years), and age at first full-term pregnancy (median 20 years). The association of increased risk with higher BMI at age 20 years remained significant after stratification for menopause (premenopausal: OR 1.41 95 % CI 1.10-1.81, P = 0.01; postmenopausal: OR 1.38 95 % CI 1.06-1.80, P = 0.02). Late age at menarche and prolonged lifelong lactation were associated with a risk reduction among premenopausal women (ORmenarche 0.74 95 % CI 0.56-1.00, P = 0.05; ORlactation 0.98 95 % CI 0.97-0.99, P <0.01). The adjusted logistic regression estimated an increased risk for a Fatty Diet , characterized by a higher consumption of milk, vegetable oils and fats, butter, lard, and red meat (OR = 1.42, 95 % CI 1.08 1.87; P = 0.01), and for a Fruity Diet characterized by a higher consumption of fish, mango, papaya, avocado, and watery fruits (OR = 1.61, 95 % CI 1.14-2.28; P = 0.01). Both diets showed an inverse association with the ratio between polyunsaturated and saturated fatty acids (P/S ratio). The risk estimations changed after splitting the study population into three BMI groups (<24 kg/m², 24 - 26 kg/m² and >26 kg/m²). In the lowest BMI group risk estimations showed large confidence intervals and indicated that the group might be too small for reliable estimations. In the BMI group 24-26 kg/m² all previously identified risk associations changed to no risk associations but menopausal status. The increased risk association for Fatty Diet remained significantly in the BMI group >26 kg/m² only.Long-standing lactation and reproductive behaviour are associated with a lower breast cancer risk in the region. As current changes in lifestyle affect age at menarche, reproductive behaviour, and nutritional status, an increased incidence of breast cancer is to be expected. Preventive efforts should include advice on reproductive and breastfeeding behaviour. A diet characterised by a low P/S ratio seems to be more important for the development of breast cancer than total fat intake.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Breast Cancer Research and Treatment Doi 10.1007/s10549-010-1255-7