Q1 individuals (O3I < 4.3%) showed slightly attenuated risk to AD and all cause dementia progression than Q5 individuals (O3I > 7.1%) Using O3I (or RBC EPA) as the exposure of interest resulted in weaker and non-significant associations than DHA alone an increase in RBC DHA from Q1 to Q5 provides 4.7 additional years free of AD (higher benefit in APOE-ε4 carriers). Here, APOE is linked to Alzheimer disease.