An irregular circadian rhythm can have a negative effect on a person’s ability to sleep and function properly, and can result in a number of health problems, including mood disorders such as depression and anxiety.
A recent study suggested that the night-owl type might have a greater predisposition to psychological disturbances. The authors found that the different circadian types were likely to have different coping styles to emotional stressors, and the ones adopted by the morning larks seemed to result in better outcomes and fewer psychological problems. This was a correlational study, so the reason for adopting different styles wasn’t explained, but this study emphasizes the great impact circadian rhythms have on health and functioning.
Most of the evidence on the relationship between mood problems and circadian rhythm comes from studies of shift workers, whose sleep periods are out of sync with their circadian rhythm. Multiple studies show an increased prevalence of depression in night-shift workers. One meta-analysis showed that night-shift workers are 40% more likely to develop depression than daytime workers. Conversely, circadian rhythm disturbances are common in people with depression, who often have changes in the pattern of their sleep, their hormone rhythms, and body temperature rhythms.