New research has revealed that as mice age, the biological clock in their stem cells remains just as active but shifts focus onto other cell processes. It becomes less concerned with maintaining tissue and more involved in dealing with stress, carrying out such functions as repairing damaged DNA. The findings may explain why mice age at a slower pace when put on a low-calorie diet, say the researchers. They suggest that calorie restriction delays the changes in circadian functions that occur in cells during aging. The research team, including members from the Institute for Research in Biomedicine (IRB) Barcelona in Spain and the University of California, Irvine, reports the findings in two papers published in the journal Cell.