Mutations are changes in the molecular “letters” that make up DNA, the genetic blueprint for cells. Mutations build up with age in every cell when DNA is damaged or when cells make mistakes in fixing or copying it. Most mutations are harmless, but when they disrupt genes, they can cause cancer and other diseases.

Past studies in animals have shown that a large reduction in the number of calories they consume, called caloric restriction, extends their lifespans and slows aspects of aging. But whether caloric restriction also slows the rate at which mutations occur with age had not been investigated across the genome, the complete set of genetic material present in every cell.