The relationship between trajectories of serum lipids and cognitive impairment in middle aged and elderly: A 6-year prospective cohort study in Xi'an, China

Background: Hyperlipidemia has been linked to cognitive impairment (CogI) caused by Alzheimer's disease and vascular disease. Nevertheless the relationship between long-term trajectories of serum lipids and the risk of developing CogI is still lacking. Methods: Research enrolled participants aged 40 years or older in the suburbs of Xi'an, China and conducted follow-ups every two years from 2014 to 2020. Fasting serum lipid (including total cholesterol, TC; triglyceride, TG; high density lipoprotein, HDL-c; low density lipoprotein, LDL-c) levels were tested. Those with normal cognition at baseline and diagnosed with MCI or dementia during follow-up were defined as having new-onset CogI. We used group-based trajectory model for serum lipid trajectory classification, and multivariable logistic regression models to investigate the relationship between long-term serum lipids trajectories and CogI. Results: Our final sample included 1268 participants. There were 33 (2.6%) new-onset CogI of whom 20 met the criteria for MCI and 13 met the criteria for dementia during the follow-up. Trajectories of TC and LDL-c were divided into three categories (low, medium and high level) respectively; lgTG and HDL-c were divided into low and high level respectively. Univariate analysis showed that the incidence rate of CogI in low TC group (3.4%) or high TC group (4.3%) was higher than that in medium TC group (1.5%). Multivariable logistic regression analysis showed that compared to medium level, the risk of developing CogI was increased for both low TC level (OR = 2.679 [95% CI, 1.140–6.295]) and high TC level (OR = 2.828 [95% CI, 0.927–8.624]). Other lipid trajectory levels were not associated with the risk of developing CogI. Conclusions: Long-term low or high TC levels may be a predictive factor for the risk of CogI.