Background: Despite the high saturated fat content of dairy products, no clear association between dairy product intake and risk of myocardial infarction (MI) has been observed. Dairy products are the main source of conjugated linoleic acid (CLA; 18:2n-7t), which is produced by the ruminal biohydrogenation of grasses eaten by cows. Pasture-grazing dairy cows have more CLA in their milk than do grain-fed cows. Some animal models have reported beneficial effects of CLA on atherosclerosis.
Objective: The objective was to determine the association between the 9c,11t-CLA isomer in adipose tissue and risk of MI.
Design: The studied population consisted of 1813 incident cases of a first nonfatal acute MI and 1813 population-based controls matched for age, sex, and area of residence. All subjects lived in Costa Rica-a country that uses traditional pasture-grazing for dairy cows. Conditional logistic regression was used to estimate multivariate odds ratios and 95% CIs.
Results: Adipose tissue 9c,11t-CLA was associated with a lower risk of MI in basic and multivariate models. Compared with the lowest quintile, odds ratios and 95% CIs were 0.80 (0.61, 1.04) for the second, 0.86 (0.64, 1.14) for the third, 0.62 (0.46, 0.84) for the fourth, and 0.51 (0.36, 0.71) for the fifth quintiles (P for trend <0.0001). Dairy intake was not associated with risk of MI, despite a strong risk associated with saturated fat intake.
Conclusion: 9c,11t-CLA, which is present in meaningful amounts in the milk of pasture-grazed cows, might offset the adverse effect of the saturated fat content of dairy products.