Inverse association between dietary and serum conjugated linoleic acid andrisk of breast cancer in postmenopausal women

Conjugated linoleic acid (CLA) is anticarcinogenic in experimental animal s tudies. We studied dietary and serum CLA in Finnish patients with breast ca ncer in 1992-1995. Participants were consecutive women with breast cancer ( 68 premenopausal and 127 postmenopausal) and population-based control women (75 premenopausal and 133 postmenopausal), matched for age and area of res idence. Diet was assessed by a validated food frequency questionnaire and t he fatty acid composition of serum by gas-liquid chromatography. In postmen opausal women, dietary CLA, serum CLA, myristic acid, and trans-vaccenic ac id were significantly lower in cases than in controls. The odds ratio for b reast cancer in the highest quintile vs. the lowest was 0.4 [95% confidence interval (CI) = 0.2-0.9] for CLA, 0.3 (95% CI = 0.1-0.7) for myristic acid , and 0.3 (95% CI = 0.1-0.7) for trans-vaccenic acid in serum. The odds rat ios remained similar after adjustment for known risk factors of breast canc er. A diet composed of CLA-rich foods, particularly cheese, may protect aga inst breast cancer in postmenopausal women, but it is impossible to assess the independent effects of CLA in this study. The findings may be of releva nce for food production, inasmuch as it is possible to increase CLA and its precursor trans-vaccenic acid in foods by modifying the feeding of ruminan ts.