Statins and serum cholesterol's associations with incident dementia and mild cognitive impairment

BACKGROUND: Statin use and serum cholesterol reduction have been proposed as preventions for dementia and mild cognitive impairment (MCI). METHODS: 1604 and 1345 eligible participants from the Baltimore Longitudinal Study of Aging (BLSA) were followed after age 50 for a median time of around 25 years, to examine the incidence of dementia (n=259) and MCI (n=138), respectively. Statin use (ever-use and time-dependent use), total cholesterol levels (TC; first visit and time-dependent), TC change trajectory from first visit and high-density lipoprotein (HDL-C):TC ratio (first visit and time-dependent) were the main exposures of interest. Cox proportional hazards models were used. RESULTS: Participants with incident dementia had a higher first-visit TC compared with participants who remained free of dementia and MCI, while first-visit TC was higher among statin ever-users compared with never-users (age-unadjusted associations). Statin users had a two- to threefold lower risk of developing dementia (HR=0.41; 95% CI 0.18 to 0.92), but not MCI, when considering time-dependent 'statin use' with propensity score model adjustment. This association remained significant independently of serum cholesterol exposures. An elevated first-visit TC was associated with reduced MCI risk (upper quartile (Q(4)) vs Q(1): HR=0.51; 95% CI 0.29 to 0.90). Compared with the lowest quartile (Q(1): 0.00-0.19), HDL-C:TC (time-dependent) in (Q(2): 0.19-0.24) was associated with reduced MCI risk (HR=0.58; 95% CI 0.34 to 0.98). Among men only, TC decline from first visit was significantly associated with increased dementia risk (HR=4.21; 95% CI 1.28 to 13.85). CONCLUSIONS: Statins may have multifactorial effects on dementia but not MCI risk. Future interventions may be warranted, and research should focus on optimal serum TC, HDL-C:TC ratio and TC change trajectories.