Researchers at the Federal University of Rio de Janeiro, working in mice and with donated human brain tissue, studied irisin, a hormone muscle releases during exercise, to see whether it reaches the brain and does anything once it gets there.
In the peer-reviewed study, irisin levels were lower in the hippocampus of people who had died with Alzheimer's disease than in those who had not, and in mice engineered to develop the disease, raising brain irisin restored normal memory performance and protected the connections between neurons, while blocking it weakened the protective effects of exercise.
The pattern suggested irisin is one of the molecules carrying exercise's protective effect from muscle to brain, and that losing it may be part of why Alzheimer's disease progresses. The human data came from brain tissue donated after death, which can show association but not cause, and the memory rescue was shown only in mice, so a drug based on irisin for people remains unproven.
Read the original study
Lourenco et al., Nature Medicine, 2019 · doi.org/10.1038/s41591-018-0275-4
A muscle hormone, reaching all the way to memory.
Source
- Lourenco, M. V., Frozza, R. L., de Freitas, G. B., Zhang, H., Kincheski, G. C., Ribeiro, F. C., Gonçalves, R. A., Clarke, J. R., Beckman, D., Staniszewski, A., Berman, H., Guerra, L. A., Forny-Germano, L., Meier, S., Wilcock, D. M., de Souza, J. M., Alves-Leon, S., Prado, V. F., Prado, M. A. M., . . . De Felice, F. G. (2019). Exercise-linked FNDC5/irisin rescues synaptic plasticity and memory defects in Alzheimer's models. Nature Medicine, 25(1), 165–175. https://doi.org/10.1038/s41591-018-0275-4