[4][8] However, despite lack of an official diagnosis of sundown syndrome in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), there is currently a wide range of reported prevalence.
[11] In humans, sunset triggers a biochemical cascade that involves a reduction of dopamine levels and a shift towards melatonin production as the body prepares for sleep.
Other causes or precipitating factors that may lead to sundown syndrome may include hormonal changes, disturbances in REM sleep, individual and/or caregiver fatigue, inappropriate medication use, or being predisposed to behavioral disorders from chronic neurological diseases.
A reduced number of staff in the evening can be attributed to more unmet needs and a lower threshold for agitation for individuals with sundown syndrome.
[14] People with established sundowning and no obvious medical illness may be suffering from impaired circadian regulation, or may be affected by nocturnal aspects of their institutional environment such as shift changes, increased noise, or reduced staffing (which leads to fewer opportunities for social interaction).
[12] Serotonin has also been observed to potentially have a key role in the regulation of circadian rhythm as research has shown that serotonergic agonism in the SCN results in "phase shifts" in portions of the light-dark cycle.