Interaction between lipoprotein (a) levels and body mass index in first incident acute myocardial infarction

Background Possible interaction between Lipoprotein (a) (Lp(a)) and body mass index (BMI) was investigated with regard to the risk of first incident acute myocardial infarction (AMI). Methods Cross-sectional study of 1522 cases with initial AMI and 1691 controls without coronary artery disease (CAD) were retrospectively analyzed using logistic regression model. Subjects were categorized based on Lp(a) and BMI and compared with regard to occurrence of AMI by calculating odds ratios (ORs) with 95% confidence intervals (CIs). A potential interaction between Lp(a) and BMI was evaluated by the measures of effect modification on both additive (Relative excess risk due to interaction, RERI) and multiplicative scales. Results Compared with reference group (BMI < 24 kg/m 2 and in the first quintile of Lp(a)), multivariable-adjusted analysis revealed that ORs(95%CI) of AMI were 2.27(1.46–3.52) for higher BMI alone; 1.79(1.11–2.90), 1.65(1.05–2.60), 1.96(1.20–3.20) and 2.34(1.47–3.71) for higher Lp(a) alone across its quintiles; and 2.86(1.85–4.40), 3.30(2.14–5.11), 4.43(2.76–7.09) and 5.98(3.72–9.60) for both higher BMI and higher Lp(a), greater than the sum of the both risks each. Prominent interaction was found between Lp(a) and BMI on additive scale (RERI = 2.45 (0.36–4.54) at the fifth quintile of Lp(a)) but not on multiplicative scale. Conclusions This study demonstrates that BMI and Lp(a) levels are important factors affecting the risk of AMI. Significant interaction is found between Lp(a) and BMI in initial AMI on additive scale, indicating that Lp(a) confers greater risk for initial AMI when BMI is elevated. For those whose BMIs are inadequately controlled, Lp(a) lowering may be an option. Trial registration This clinical study was not registered in a publicly available registry because this study was a retrospective study first started in 2015. Data are available via the correspondent.