Working night shift poses cancer risk.

• Position: Circadian Rhythms - Brief article

A handful of large studies of cancer risk factors have found that working the night shift--as nearly 15% of Americans do--boosts the chances of developing cancer. Pathologist Thales Papagiannakopoulos has discovered a link that may explain this heightened risk.

In humans and most other organisms, a circadian clock governed by light regulates the timing of key aspects of human physiology by controlling cellular activities, such as metabolism and division.

In a study, researchers found that two of the genes that control cells' circadian rhythms also function as tumor suppressors. Loss of these tumor suppressors, either through gene deletion or disruption of the normal light/dark cycle, allows tumors to become more aggressive. "It doesn't matter how you disrupt the clock--both ways, loss of it seems to drive tumorigenesis," says Papagiannakopoulos in Cell Metabolism.

In humans, the central circadian clock is located in the brain's suprachiasmatic nucleus (SCN), which receives information about light levels...