This study aims to analyze the probiotic's effect on neurocognitive function and markers of oxidative stress in Alzheimer's disease (AD) patients.

AD, being a progressive neurodegenerative disease, constitutes nearly 70% of all the cases related to dementia. Different oxidative stress reduction therapies are being discussed for AD including probiotics.

PubMed, Cochrane Central, and ScienceDirect were searched till September 2024. The cognitive outcome of interest was the Mini-Mental State Examination (MMSE) score while the metabolic and oxidative outcomes of interest were levels of glutathione (GSH), nitric oxide (NO), malondialdehyde (MAD), total antioxidant capacity (TAC), homeostatic model of assessment for insulin resistance (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), triglycerides (TAG) and total cholesterol. Statistical analysis was performed on Review Manager version 5.4.1 employing a random effects model. The Cochrane RoB 2.0 tool was used for quality assessment.

Five randomized clinical trials were included in the final analysis. The results depict that the MMSE score (MD = 2.49; 95% CI:[0.44,4.53] ; p = 0.02; I² = 85%) and GSH levels (MD = 17.78 µmol/L, 95% CI: [3.07,32.50]; p=0.02; I²=0%) were significantly higher in the probiotics group. Probiotics also resulted in reduced MAD (MD = -1.54 µmol/L, 95% CI;[-2.31,-0.78] ; p<0.0001; I² =95%), HOMA-IR (MD =-0.30, 95% CI:[-0.55,-0.05]; p=0.02; I² =0%) and an increase in QUICKI (MD =0.01, 95% CI:[0.00,0.01]; p=0.03; I² =0%) levels compared to placebo. Other outcomes like TAC (MD =-0.80 mmol/L, 95% CI:[-101.78,100.19]; p=0.99; I² =84%), NO (MD =-0.64 µmol/L, 95% CI:[-2.92,1.63]; p=0.58; I² =31%), TAG  (MD =-14.55 mg/dL, 95% CI:[-30.73,1.63]; p=0.08; I² =0%), total cholesterol  (MD =-3.98 mg/dL, 95% CI:[-15.68,7.71]; p=0.50; I² =0%) were comparable between two groups.

Probiotics improved neurocognitive function in AD patients. They also increased antioxidants like GSH, reduced inflammatory markers like MAD, and lowered insulin resistance.