Overview

The aim of this clinical trial is to investigate the effects of L-serine supplementation on cognitive decline and psychosocial functioning in older adults with late-life depression (LLD). The study will evaluate changes in depressive symptoms, neural and cognitive functioning, and will assess neurophysiological, metagenomic, and biochemical alterations associated with L-serine supplementation compared with placebo.

The main research questions are:

• Does L-serine supplementation affect cognitive function, depressive symptoms, and neural functioning in individuals with late-life depression?
• What biological mechanisms may underlie the effects of L-serine on cognitive decline? Participants will be randomly assigned to one of two study arms: an intervention group (total n = 42) receiving L-serine at a dose of 6 g/day for 48 weeks, and a placebo group (total n = 42) receiving 6 g/day of maltodextrin for the same duration.

All participants will be assessed at three time points: T0 (baseline, prior to trial initiation), T18 (after 18 weeks), and T48 (after 48 weeks, at the end of the trial).

At each assessment, participants will:

• complete clinical questionnaires and a neuropsychological assessment;
• provide blood, fecal, and urine samples;
• undergo electroencephalographic (EEG) recordings.

Eligibility

Inclusion Criteria:

• Age 65-85 years;
• Presence of depressive symptoms, defined as a score ≥ 5 on the Geriatric Depression Scale-15 items (GDS-15) or ≥ 5 on the Patient Health Questionnaire-9 (PHQ-9).

Exclusion Criteria:

• Diagnosis of dementia;
• Use of antibiotics or anti-inflammatory medications within the previous 8 weeks;
• Active gastrointestinal disease;
• Severe chronic medical conditions (e.g., advanced-stage cancer, severe cardiac or renal disorders, or other debilitating diseases);
• Renal dysfunction;
• Current alcohol or substance abuse;
• Major surgical procedures within the previous 6 months.