Association between Dyslipidaemia and Cognitive Impairment: A Meta-Analysis of Cohort and Case-Control Studies

Background: This study explored the specific relationship between different lipid indicators and cognitive impairment and aimed to provide a reference for implementing targeted lipid regulation measures to prevent and alleviate cognitive impairment. Methods: We searched three databases (PubMed, Embase, and Web of Science) for literature related to hyperlipidaemia, lipid levels, and cognitive impairment, and used the Newcastle-Ottawa Scale to evaluate the quality of the identified literature. A meta-analysis was performed using RevMan 5.4, and the combined effect size ratio using a random-effects model (odds ratio [OR] and 95% confidence interval [CI]) was used to evaluate the association between dyslipidaemia and cognitive impairment. Results: Among initially identified 2247 papers, we ultimately included 18 studies involving a total of 758,074 patients. The results of the meta-analysis revealed that patients with hyperlipidaemia had a 1.23-fold higher risk of cognitive impairment than those with normal lipid levels (OR = 1.23, 95% CI: 1.04–1.47, p = 0.02). Further subgroup analysis showed that elevated total cholesterol (TC) levels increased the risk of cognitive impairment by 1.59-fold (OR = 1.59, 95% CI: 1.27–2.01, p < 0.0001) and were more significant in older or male patients. Moreover, elevated triglyceride levels were inversely correlated with cognitive disorders, whereas elevated low-density lipoprotein cholesterol levels were unrelated to cognitive impairment risk. Conclusions: Dyslipidaemia was strongly associated with cognitive impairment, and elevated TC levels were a risk factor for cognitive impairment. Furthermore, the damaging effects of elevated TC levels on cognition were more pronounced in older and male populations.