A multistrain probiotic lowered a tau blood marker and preserved drawing skills in a 24-week Korean trial; global cognition didn't differ.

A 24-week, double-blind, placebo-controlled trial in 87 older adults with early cognitive impairment found that a multistrain probiotic shifted a blood marker tied to Alzheimer's pathology and preserved drawing-and-copying skills the placebo group lost. Global cognition, verbal memory, and executive function were unchanged between arms.

The trial drew from South Korea's Gwangju Alzheimer's Disease and Related Dementias (GARD) cohort: 40 participants on a multistrain probiotic, 47 on placebo. Plasma pTau181, a protein tracking tau tangle burden, fell more in the probiotic arm (between-group p < 0.001, PubMed 42663491). Plasma GFAP and NfL, inflammation and nerve-injury markers, stayed flat on probiotics; in placebo, both rose (within-group p = 0.014 and p = 0.041).

The clinical dementia rating memory subscore improved on probiotics versus placebo (p = 0.010). Visuospatial tasks followed: Constructional Praxis improved (p = 0.036), Rey-Osterrieth copy improved (p = 0.027), and delayed figure recall was preserved on probiotics; the placebo arm declined (p = 0.025).

The authors call this a gut-brain axis signal and a non-pharmacological adjunct candidate, not a treatment. The pattern is one site, six months, 87 people; durability, mechanism, and broader replication remain open. Readers worried about memory should bring the study to a clinician rather than start a supplement on this single trial.