U-shaped association between low-density lipoprotein cholesterol levels and risk of all-cause mortality mediated by post-stroke infection in acute ischemic stroke

During the acute stage of ischemic stroke, it remains unclear how to interpret the low low-density lipoprotein cholesterol (LDL-C) level. We aimed to evaluate the association between LDL-C levels, post-stroke infection, and all-cause mortality. 804,855 ischemic stroke patients were included. Associations between LDL-C levels, infection, and mortality risk were estimated by multivariate logistic regression models and displayed by restricted cubic spline curves. Mediation analysis was performed under counterfactual framework to elucidate the mediation effect of post-stroke infection. The association between LDL-C and mortality risk was U-shaped. The nadir in LDL-C level with the lowest mortality risk was 2.67 mmol/L. Compared with the group with LDL-C = 2.50-2.99 mmol/L, the multivariable-adjusted odds ratio for mortality was 2.22 (95% confidence intervals (CI): 1.77-2.79) for LDL-C <1.0 mmol/L and 1.22 (95% CI: 0.98-1.50) for LDL-C ≥5.0 mmol/L. The association between LDL-C and all-cause mortality was 38.20% (95% CI: 5.96-70.45, P = 0.020) mediated by infection. After stepwise excluding patients with increasing numbers of cardiovascular risk factors, the U-shaped association between LDL-C and all-cause mortality and the mediation effects of infection remained consistent with the primary analysis, but the LDL-C interval with the lowest mortality risk increased progressively. The mediation effects of infection were largely consistent with the primary analysis in subgroups of age ≥65 years, female, body mass index <25 kg/m², and National Institutes of Health Stroke Scale ≥16. During the acute stage of ischemic stroke, there is a U-shaped association between LDL-C level and all-cause mortality, where post-stroke infection is an important mediating mechanism.