Background: The protein digestibility-corrected amino acid score (PDCAAS) represents the degree of utilizable dietary protein, namely the protein quality. The PDCAAS of a diet is required to be evaluated on a meal-by-meal basis, as food digestion and absorption occur with each meal intake. Although a positive association between protein intake and cognitive function has been reported, no study has investigated the association between PDCAAS of a diet and cognitive function.
Objectives: To investigate the relationship between PDCAAS of a diet and cognitive impairment in older adults.
Design: Longitudinal epidemiological study.
Setting: Community-based setting.
Participants: We analyzed 541 community-dwellers who participated in both baseline and follow-up survey. They were 60-83 years of age without cognitive impairment at baseline.
Measurements: Cognitive impairment was defined as a Mini-Mental State Examination (MMSE) score ≤27. Individual PDCAASs were calculated for each of three regular meals from the 3-day dietary records at baseline. Participants were classified into two groups according to the sex-specific tertiles (T1-T3) of the PDCAAS for each meal (i.e., T1 as the low score group and T2-T3 as the medium and high score group). The dependent variable was cognitive impairment observed after 4 years, and the explanatory variables were the PDCAAS groups for each meal (the medium and high group as the reference) and covariates (sex, age, body mass index, education, depressive symptoms, medical history, protein intake at each meal, and the MMSE score at baseline). Multivariable logistic regression analysis was performed to evaluate the low PDCAAS group for cognitive impairment after 4 years.
Results: A significant association was observed only between a low PDCAAS of breakfast and the incidence of cognitive impairment (the adjusted odds ratios [95% confidence intervals] of low PDCAAS for cognitive impairment for breakfast, lunch, and dinner were 1.58 [1.00-2.50], 0.85 [0.54-1.34], and 1.08 [0.71-1.65], respectively).
Conclusion: A lower PDCAAS of breakfast, i.e., a diet with poor quality of protein, was associated with the incidence of cognitive impairment in older adults of the community.
Keywords: Protein quality; aging; cognition; dietary amino acid; three regular meals.