Changes in salivary brain-derived neurotrophic factor following a standardized eating task in community-dwelling...

While mastication is suggested to influence cognitive function, evidence regarding its relationship with brain-derived neurotrophic factor (BDNF) in humans remains limited, particularly regarding the utility of salivary BDNF. This study investigated changes in salivary BDNF concentrations following a standardized eating task and examined their association with plasma BDNF levels in community-dwelling older adults. This cross-sectional study, nested within a cohort, included 116 older adults (median age, 76 years [interquartile range, 70-81]; 53 men and 63 women). Venous blood samples were collected before the eating task, and saliva samples were collected before and after a standardized rice-ball eating task. Mature BDNF concentrations were measured using ELISA. Changes in absolute and total protein-corrected salivary BDNF concentrations before and after the standardized eating task were assessed using the Wilcoxon signed-rank test. The association between plasma and baseline salivary BDNF concentrations was evaluated using Spearman's rank correlation coefficients (ρ). Salivary BDNF concentrations significantly decreased after the standardized eating task compared to baseline (median, 1.4 vs. 0.9 pg/mL; p < 0.001). Total protein-corrected salivary BDNF levels were also significantly lower (p = 0.001). No significant correlations were observed between plasma BDNF and baseline salivary BDNF concentrations (ρ = 0.034, p = 0.723) or protein-corrected salivary BDNF concentrations (ρ = 0.046, p = 0.634). Salivary BDNF levels significantly decreased after the standardized eating task and did not correlate with plasma BDNF levels. These findings suggest that salivary BDNF is influenced by local biological processes associated with food intake and mastication; therefore, it may not serve as a simple surrogate marker for systemic BDNF levels in older adults.