Dietary fats and the APOE-e4 risk allele in relation to cognitive decline: a longitudinal investigation in a biracial population sample

Background APOE-e4 is the strongest genetic risk factor for Alzheimer's disease. However, the influence of APOE-e4 on dietary fat intake and cognition has not been investigated. Objective We aim to examine the association of types of dietary fat and their association to cognitive decline among those with and without the APOE-e4 allele. Methods The study included 3,360 Chicago Health and Aging Project (CHAP) participants from four Southside Chicago communities. Global cognition was assessed using a composite score of episodic memory, perceptual speed, MMSE, and diet using a 144-item food frequency questionnaire. APOE genotype was assessed by the hME Sequenom mass-array platform. Longitudinal mixed-effect regression models were used to examine the association of dietary fat and the APOE-e4 allele with cognitive decline, adjusted for age, sex, education, smoking status, and calorie intake. Results The present study involved 3,360 participants with a mean age of 74 at baseline, 62% African Americans, 63% females, and a mean follow-up of 7.8 years. Among participants with the APOE-e4 risk allele, higher intakes of total and saturated fat (SFA) were associated with a faster decline in global cognition. Among individuals with the APOE-e4 risk allele, a 5% increase in calories from SFA was associated with a 21% faster decline (β = −0.0197, P = 0.0038). In contrast, a higher intake of long-chain n-3 polyunsaturated fatty acids (LC-n3 PUFA) was associated with a slower rate of decline in global cognition among APOE-e4 carriers. Specifically, for every 1% energy increment from LC-n3 PUFA, the annual rate of global cognitive decline was slower by 0.024 standardized unit (SD 0.010, P = 0.023), about 30.4% slower annual cognitive decline. Higher SFA or other types of dietary fat were not associated with cognitive decline among APOE-e4 non-carriers. Conclusions Our study found a significant association between SFA and faster cognitive decline, LC-n3 PUFA and slower cognitive decline among those with the APOE-e4 allele. Our findings suggested that higher intake of SFA might contribute faster cognitive decline in combination with APOE-e4 whereas LC-n3 PUFA might compensate the adverse effects of APOE-e4. The interaction between intakes of different types of dietary fat and APOE-e4 on cognitive function warrants further research.