Background: Studies in animals and in vitro suggest that conjugated linoleic acids (CLAs), a group of fatty acids found mainly in dairy products and in the meat of ruminants, have protective effects against mammary carcinogenesis. However, findings from epidemiologic studies on CLA intake in relation to breast cancer risk are sparse and inconsistent.
Objective: The objective was to examine prospectively the association between CLA intake and the incidence of invasive breast cancer in the Swedish Mammography Cohort.
Design: In 1987-1990, 61,433 cancer-free women completed a food-frequency questionnaire from which we estimated each woman's CLA intake. Cox proportional hazards models were used to estimate relative risks, adjusted for breast cancer risk factors.
Results: During a mean follow-up of 17.4 y, 2952 incident cases of breast cancer were ascertained. In multivariate analyses, no significant association was observed between dietary CLA intake and risk of breast cancer, overall or by estrogen receptor (ER) and progesterone receptor (PR) status. The multivariate relative risks (95% CI) for the highest quintile of CLA intake (> or =155.7 mg/d) compared with the lowest quintile (<78.1 mg/d) were 1.04 (0.92, 1.17) for overall breast cancer, 1.09 (0.90, 1.31) for ER+/PR+ tumors, 1.09 (0.78, 1.53) for ER+/PR- tumors, and 0.84 (0.57, 1.24) for ER-/PR- tumors.
Conclusion: The results provide no evidence of a protective effect of CLA against breast cancer development in women.