Objective: To estimate the postmenopausal breast cancer risk associated with total fat intake, different types and relative proportions of dietary fat using a nested, matched case-control study within the Malmö Diet and Cancer (MDC) cohort, Sweden.
Methods: Among women 50 years or older at baseline (n = 12,803), incident breast cancer cases (n = 237) were matched to controls (n = 673) on age and screening date. Data were obtained by a "novel" diet history method, a structured questionnaire, and anthropometric measurements. Conditional logistic regression examined breast cancer risks associated with quintiles of fat intake residuals adjusted for energy and potential confounders.
Results: Saturated fat and the omega3-omega6 fatty acid ratio were not related to increased risks, but positive trends were seen for total (p = 0.031), monounsaturated (p = 0.002), and polyunsaturated fat (p = 0.0009), especially omega6 fatty acids and the polyunsaturated-saturated fat ratio (p = 0.004). With mutual adjustment for different types of fat, an elevated risk remained significant in the highest omega6 fatty acid quintile (RR= 2.08, 95% CI 1.08-4.01).
Conclusions: Postmenopausal breast cancer was positively associated with total, monounsaturated, and polyunsaturated fat. However, with mutual adjustment for other types of fat, specifically high intakes of omega6 fatty acids were associated with an increased risk.