Why do our bodies age at different rates? Why can some people run marathons at the age of 70, while others are forced to use a walker?

Genes are only part of the answer. A trio of scientists from the University of North Carolina argue in a new paper that more work needs to be done on "gerontogens"—factors, including substances in the environment, that can accelerate the aging process.

Possible gerontogens include arsenic in groundwater, benzene in industrial emissions, ultraviolet radiation in sunlight, and the cocktail of 4,000 toxic chemicals in tobacco smoke. Activities may also be included, like ingesting excessive calories, or suffering psychological stress.

Writing in Trends in Molecular Medicine, Jessica Sorrentino, Hanna Sanoff, and Norman Sharpless argue