¹Dongguk University Medical School, Psychiatry, Gyeongju, Korea, Republic of

Background: As population aging accelerates, cognitive decline in community-dwelling older adults with normal cognition and mild cognitive impairment has become a significant public health issue. Transcranial direct current stimulation (tDCS) is a safe, non-invasive intervention with potential cognitive benefits, but evidence on its long-term effects is limited.

Aims & Objectives: This study aimed to determine the long-term effects of transcranial direct current stimulation (tDCS) on cognitive function over a three-year period and to identify the optimal duration of cognitive intervention in community-dwelling elderly individuals with normal cognition (NC) and mild cognitive impairment (MCI).

Method: A total of 519 community-dwelling elderly participants aged over 65 years were divided into three groups according to cognitive status and duration of intervention. Demographic characteristics were analyzed. Cognitive function was assessed using the Cognitive Impairment Screening Test for Dementia Screening, the Global Deterioration Scale, and the Subjective Memory Complaint Questionnaire. Activities of daily living were evaluated using the Seoul-Instrumental Activities of Daily Living scale; quality of life using the Korean Quality of Life–Alzheimer’s Disease scale; and depression using the Short Korean Form of the Geriatric Depression Scale. The intervention program consisted of 30 sessions per year (once weekly) conducted annually from January to November. Data analyses were performed at four time points.

Results: Significant improvements in cognitive function and quality of life were observed in both the NC and MCI groups when comparing post-intervention periods with participation periods. Significant differences were found between one year and two to three years of participation (p < 0.001), whereas no significant differences were observed between two and three years. In the MCI group, changes in activities of daily living differed significantly between one year and two to three years of participation (p < 0.001). Emotional state and attitudes toward dementia did not vary according to the duration of participation.

Discussion & Conclusions: These findings suggest that transcranial direct current stimulation is effective in improving cognitive function, activities of daily living, depression, and quality of life regardless of intervention duration. However, a two-year intervention period may be optimal when considering the sustainability of public services, budget constraints, and efficient resource utilization.