Reproductive history and dietary habits and breast cancer risk in Greenlandic Inuit: a case control study.

ABSTRACT

BACKGROUND: The incidence of breast cancer in Greenland has increased considerably since 1970. It has been suggested that the previous low incidence is associated with the traditional lifestyle and marine food diet, and that the increase in breast cancer risk may be due to changes to a more westernized diet and lifestyle. OBJECTIVE: To investigate the relation between food intake, reproductive factors and the risk of breast cancer in Greenlandic Inuit women. DESIGN: A case control study with participants from all regions of Greenland. The sampling was carried out at Dronning Ingrids Hospital in Nuuk, Greenland where all breast cancer cases are treated. The reproductive factors and dietary intake were assessed using a questionnaire completed at enrolment. Student t-test was used to compare group differences for continuous data. Fisher's exact test and Pearson's Chi-square were used to compare distribution frequency of data between groups. Odd ratios (ORs) were obtained using logistic regression. Estimates with a P-value ≤0.05 were considered significant. RESULTS: Information on reproductive factors and dietary intake was available for 116 participants, 60 breast cancer cases and 56 controls. We found that the risk of having breast cancer was significantly reduced (OR 0.24 [95% CI 0.09; 0.66]) for the group with ≥3 full-term pregnancies and breastfeeding duration of ≥6 months compared to the group with ≤2 full-term pregnancies and breastfeeding duration of <6 months. We found that intake of fruit and vegetables when analyzed together, significantly reduced breast cancer risk (OR 0.22 [95% CI 0.05; 0.98]). CONCLUSIONS: Higher parity, longer breastfeeding duration and intake of fruit and vegetables were protective factors for breast cancer risk. No clear associations between breast cancer and traditional or other imported food were seen.