From ScienceDaily: "A new paper from MIT biology professor Leonard Guarente strengthens the link between longevity proteins called sirtuins and the lifespan-extending effects of calorie restriction. ... Sirtuins bring about the effects of calorie restriction on a brain system, known as the somatotropic signaling axis, that controls growth and influences lifespan length. ... The researchers genetically engineered mice whose ability to produce the major mammalian sirtuin SIRT1 in the brain was greatly reduced. Those mice and normal mice were placed on a calorie-restricted diet. The normal mice showed much lower levels of circulating growth hormones, demonstrating that their somatotropic signaling system was impaired, but calorie restriction had no effect on hormone levels of mice that could not produce SIRT1. In future work, Guarente plans to investigate the mechanism by which sirtuins regulate the somatotropic axis. The work could also help researchers and companies in their search for small molecules that modulate sirtuins for maximum benefit." You might recall that lowered growth hormone levels is one of the demonstrated ways to extend life span in mice.