Abstract
OBJECTIVES: Previous studies have reported a relationship between low protein intake and cognitive decline and have suggested that this association may be related to specific amino acid intake. However, the effects of amino acid intake on the maintenance of cognitive function have yet to be clarified. We examined the longitudinal association between dietary amino acid intake and cognitive function in community-dwelling older adults. DESIGN: Longitudinal epidemiological study. SETTING: Community-based setting. PARTICIPANTS: This study comprised 427 study participants aged 60-82 years with no cognitive decline, defined as a Mini-Mental State Examination (MMSE) score of >27 at baseline, who also participated in a follow-up. The average and standard deviation of the follow-up period was 8.2 ± 0.3 years. MEASUREMENTS: Dietary intake was assessed using three-day dietary records at baseline. Participants were classified into quartiles (Q1-Q4) based on the intake of 19 amino acids for males and females. Next, we classified participants into Q1 and Q2-Q4 groups. Cognitive function was assessed using the MMSE both at baseline and at follow-up. Multivariable logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between the Q1 group and cognitive decline (MMSE ≤27), using the Q2-Q4 group as a reference group. Covariates were age, sex, body mass index, years of education, severity of depressive symptoms, history of lifestyle diseases (hypertension, dyslipidemia, diabetes mellitus, stroke, and ischemic heart disease), energy intake (kcal/d), protein intake (g/d), and MMSE score at baseline. RESULTS: Cognitive decline was present in 133 (31.1%) participants. After adjustment for covariates, including total protein intake, the ORs (95% CIs) for cognitive decline were 2.40 (1.21-4.75) for lysine, 2.05 (1.02-4.09) for phenylalanine, 2.18 (1.09-4.34) for threonine, and 2.10 (1.06-4.15) for alanine. CONCLUSION: The results suggest that lysine, phenylalanine, threonine, and alanine intake is important for the maintenance of cognitive function in older people, independent of total protein intake.