Background: Although the connection between diet, lifestyle and hormones suggests that nutritional and lifestyle factors may exert an influence in the etiology of breast cancer (BC), it is not clear whether these factors operate in the same way in women with BRCA1 and BRCA2 (BRCA) gene mutations who already have an elevated BC risk.
Methods: A case-control study was conducted within a cohort of 80 French-Canadian families with 250 members involving 89 carriers of mutated BRCA gene affected with BC and 48 non-affected carriers. A validated semi-quantitative food frequency questionnaire was used to ascertain dietary intake, and a lifestyle core questionnaire, to gather information on physical activity and other lifestyle risk factors. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated in unconditional logistic regression models.
Results: After adjustment for age, maximum lifetime body mass index (BMI) and physical activity, a positive association was found between total energy intake and BRCA-related BC risk. OR was 2.76 (95%CI: 1.10-7.02; p=0.026 for trend), when comparing the highest tertile of intake with the lowest. The intake of other nutrients and dietary components was not significantly associated with the risk of BC. Age at the time the subjects reached maximum BMI was significantly related to an elevated BC risk (OR=2.90; 95%CI: 1.01-8.36; p=0.046 for trend). In addition, a direct and significant relationship was noted between maximum weight gain since both age 18 and 30 years and BC risk. The ORs were 4.64 (95%CI: 1.52-14.12; p=0.011 for trend) for weight gain since age 18 years and 4.11 (95%CI: 1.46-11.56; p=0.013 for trend) for weight gain since age 30 years, respectively. No overall association was apparent between BRCA-related BC risk and BMI, smoking, and physical activity.
Conclusion: The results of this preliminary study suggest that weight control in adulthood through dietary energy intake restriction is an important factor for the prevention of BRCA-related BC risk.