Researchers from the University of Chicago and the University of Louisville disrupted the sleep of a group of mice and found the mice developed larger, more aggressive tumors than a group of well-rested mice. The researchers theorized that fragmented sleep changes how the immune system deals with cancer in a way that makes the disease more aggressive.

The researchers also reported that the immune systems of the sleep-disrupted mice were less effective at fighting the early stages of cancer than the immune systems of the well-rested mice.