The relation between trans fatty acid levels and increased risk of myocardial infarction does not hold at lower levels of trans fatty acids in the Costa Rican food supply.

Data on the effects of recent industrial modifications that reduced the trans fatty acid (TFA) content in food supplies are scarce. In this study, incident cases (n = 1797) of a first nonfatal myocardial infarction (MI) were matched with population controls (n = 1797) for age, sex, and area of residence in Costa Rica. Odds ratio (OR) and 95% CI were calculated from conditional logistic regressions before and after a reduction of TFA in Costa Rican foods. Initially, the median quintiles of total adipose tissue TFA were 1.85, 2.47, 2.99, 3.58, and 4.40 g/100 g; total TFA was positively associated with increased MI risk after adjusting for established risk factors (OR by quintiles of total TFA: 1.00, 1.37, 1.91, 1.86, 3.28; P for trend < 0.001). This association was mostly due to 18:2 trans. In contrast, after industrial modification, median quintiles of total adipose tissue TFA were 1.84, 2.26, 2.57, 2.88, and 3.42 g/100 g; the association with MI was no longer significant (OR by quintiles of total TFA: 1.00, 0.78, 1.03, 0.88, and 1.03; P for trend = 0.65). Adipose tissue 18:1 trans fatty acids were not associated with risk of MI before or after the modification. Although to date there are no TFA regulations in Costa Rica, it appears that indirect international influence has led to a TFA reduction in the food supply and, consequently, to a reduction in the risk of nonfatal MI. The public health sector of Costa Rica should regulate food labeling and content to ensure very low levels of TFA intake.