The hormone melatonin produced by the pineal gland is today regarded as the "supreme control authority" for the day/night rhythm, because it ensures a safe long life and quality of life. Melatonin regulates the biological clock of the body and regulates the release of all important hormone.
This is how melatonin controls the ageing process as a whole.
https://de.wikipedia.org/wiki/Melatonin (Wikipedia CC-by-sa-3.0)