Long-Term Dietary Intake and Subjective Cognitive Decline

Abstract

Dementia is a neurodegenerative disease characterized by progressive decline of cognitive function and performance, leading to disability and functional dependence. In the rapidly aging world, dementia has become a leading public health concern due to the significant health-care costs and caregiver burden it contributes. However, there is still no effective treatment for dementia. To date, diet has been shown as one of the few modifiable risk factors for cognitive decline. Because current evidence on the associations between specific long-term dietary intakes and cognitive function remained inconclusive, we conducted the following research aiming to address this important issue. More than 20 years of long-term dietary intake was assessed by the semi-quantitative food frequency questionnaire (SFFQ). Subjective cognitive decline (SCD), a preclinical phase before dementia, was the outcome. The study population was two large prospective cohorts in the US, the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). In Chapter 1, we investigated the associations between long-term dietary intakes of total flavonoids, flavonoid subclass, and flavonoids-containing foods with SCD. The findings from this study provided strong evidence to further support the possible beneficial roles for flavonoids on subsequent cognitive function. To our knowledge, we were the first to report the dose-response relationship for each flavonoid subclass, which could provide important guidance for future interventional studies. In Chapter 2, the associations between total energy and dietary fat intake with SCD was examined. The results from this study showed positive associations between total energy intake and SCD, which was supported by numerous animal studies. The associations between specific fatty acid intakes and SCD were inconsistent during the follow-up period and across cohorts. Further research is needed to confirm these findings. In Chapter 3, the associations between intakes of specific protein sources, amino acids, and protein-containing foods with SCD were assessed. Higher intakes of protein, compared with total carbohydrates, were associated with lower odds of subsequent SCD. Plant-based protein was generally the superior source. Intakes of beans/legume, fish, and chicken without skin were associated with better SCD scores. These findings could have important public health implications.