An exercise-induced hormone called irisin seems to restore memory in early experiments in mice, suggesting the small peptide might be one of the reasons why physical activity may stave off memory loss in people with Alzheimer’s disease (Nat. Med. 2019, DOI:10.1038/s41591-018-0275-4). In postmortem studies, neuroscientists led by Ottavio Arancio of Columbia University and Sergio Ferreira and Fernanda De Felice of the Federal University of Rio de Janeiro found lower levels of irisin in the brains of people with advanced Alzheimer’s disease than in healthy people or people with mild neurodegeneration. The team found that mice that can’t make the irisin precursor protein have a hard time remembering objects in a memory test. Dosing them with irisin’s precursor protein rescues that memory loss. They also put mice through a daily swimming protocol and found that they expressed higher levels of irisin than mice that didn’t exercise and were less likely to have memory problems induced by amyloid β, the protein that clumps up and kills neurons in Alzheimer’s disease. The researchers suggest that modulating irisin may be one way to promote brain health.