Consistently going to bed and waking up at different times may affect our circadian rhythm, throwing our body’s various physiological processes out of sync and increasing the risk of dying in a given length of time. However, pre-existing medical conditions can also affect sleep. These inconsistent sleep habits may therefore correlate with, rather than cause, an increased risk of death over a given period.

Matthew Pase at Monash University in Melbourne, Australia, and his colleagues studied the …