People suffering from OCD (obsessive compulsive disorder)—a mental disorder where the sufferer constantly checks something or carries out the same routine—seem to share similar sleep problems, and this tends to happen more to people living in the northern hemisphere.
This is because people living in these regions get less sunlight, which makes syncing with their internal biological clock more difficult, say researchers at Binghamton University.
The researchers noted that OCD sufferers have difficulty getting to sleep and then being unable to get up on time in the morning. "People who live in areas with less sunlight may have fewer opportunities to synchronize their circadian clock, leading to increased OCD symptoms," said lead researcher Meredith Coles.
Getting up late each morning also means that people are getting less sunlight anyway, and this can become a vicious circle, leading to more eccentric sleep patterns.
(Source: Journal of Obsessive-Compulsive and Related Disorders, 2018; 18: 25)