Melatonin can slow down the effects of aging, according to a team at laboratoire Arago in Banyuls sur Mer (CNRS / Université Pierre et Marie Curie) who say that a treatment based on melatonin can delay the first signs of aging in a small mammal.Better known as the ‘time-keeping' hormone, melatonin is naturally secreted by the body during the night. It is therefore a kind of biological signal for nightfall, allowing an organism to synchronize itself with the day/night rhythm.At Laboratoire Arago, Elodie Magnanou and her co-workers studied the long-term effects of melatonin on the Greater White-toothed shrew, small nocturnal insectivorous mammals they collected in the Banyuls-sur-Mer area (Pyrenées-Orientales, France) using non-baited pitfall traps. Under normal conditions, this animal shows the first signs of aging after reaching 12 months, mainly through the loss of circadian rhythm in its activities.By continuously administering melatonin via implants, starting a little before 12 months, the appearance of these first signs was delayed by at least 3 months, which is a considerable period in relation to the lifespan of this shrew.The Greater White-toothed shrew has a lifespan of 12 to 18 months in the wild and up to 30 months in captivity. Captivity does not change the time at which signs of aging appear, it simply lengthens life.Melatonin is now known to play several beneficial roles. These include being an antioxidant, an anti-depressant, and helping to remediate sleep problems. The next step will be to understand the mode of action of the hormone on aging, so we can perhaps envisage its use on humans.Citation: Magnanou E, Attia J, Fons R, Boeuf G, Falcon J (2009) The Timing of the Shrew: Continuous Melatonin Treatment Maintains Youthful Rhythmic Activity in Aging Crocidura russula. PLoS ONE 4(6): e5904. doi:10.1371/journal.pone.0005904