Serum oxytocin correlated with later logical memory in older Japanese women: A 7-year follow-up study

OBJECTIVES: This study aimed to investigate the longitudinal relationship between serum oxytocin and logical memory among older adults in rural Japan and clarify sex differences in this relationship. MEASUREMENTS: The first survey was conducted from October 2009 to March 2011 (Time 1) and the second from November 2016 to September 2017 (Time 2). The final analysis for Time 1 included 385 participants (median age 75 years, interquartile range [IQR] 70–81 years) and that for Time 2 included 76 participants (median age 80 years, IQR 76–83 years). We assessed cognition, logical memory, and living conditions, and measured serum oxytocin levels. Logical memory was evaluated using the Wechsler Memory Scale-Revised Logical Memory II delayed recall part A (LM II-DR). Serum oxytocin was measured using the enzyme immunoassay method. RESULTS: The median (IQR) oxytocin level among men (n = 20) was 34 (16–78) pg/mL at Time 1 and 53 (28–140) pg/mL at Time 2. The median (IQR) oxytocin level among women (n = 56) was 117 (35–412) pg/mL at Time 1 and 76 (32–145) pg/mL at Time 2. The median oxytocin level among women at Time 2 was significantly lower than that at Time 1 (p = 0.004). The multivariate analysis showed that for women, LM II-DR score at Time 2 was positively associated with oxytocin level at Time 1 (p = 0.042) and negatively associated with age (p = 0.02). CONCLUSIONS: Our study suggests that maintaining high oxytocin levels in older women may prevent age-related decline in logical memory.