A low dose of the anti-ageing drug rapamycin improved blood flow to the brain in healthy middle-aged adults carrying the APOE4 gene — the strongest genetic risk factor for Alzheimer’s.

In the University of Missouri pilot trial, participants aged 45 to 65 took 1 mg of rapamycin daily for four weeks. Only APOE4 carriers showed improved cerebral blood flow; non-carriers saw no change.

The drug also reduced inflammatory markers, improved lipid metabolism and enriched gut bacteria linked to brain-healthy compounds in carriers.

APOE4 carriers often suffer reduced brain blood flow years before memory problems appear, making it an early warning sign of Alzheimer’s risk.

“If we can slow down aging in the brain for those most at risk, maybe we can reduce the risk of them developing Alzheimer’s,” said researcher Ai-Ling Lin. The paper appeared in the Journal of Cerebral Blood Flow & Metabolism.

Experts call the genotype-specific effect a promising step toward precision prevention — though larger trials are needed before any clinical use.