Dark therapy, also called scototherapy or light restriction, is a treatment which involves eliminating all light in a subject's environment, for a period of six to sixteen hours per day, in combination with a regular sleep schedule. Dark therapy manipulates circadian rhythms acting on hormones and neurotransmitters. It has been proposed recently (2005) to combine the chronobiological manipulations of light/dark and/or sleep/wake therapies with psychopharmacological medication for depression as well as for circadian rhythm sleep disorders. In the words of Anna Wirz-Justice:
Light therapy has undergone widespread controlled randomized clinical trials, and wake therapy has been so widely studied over decades that the efficacy data are strong. These nonpharmaceutical, biologically based therapies are not only powerful adjuvants, but also antidepressants in their own right... [P]ilot studies suggest that the simple measure of promoting long nights (more rest, more sleep, no light) can stop rapid cycling in bipolar patients, or diminish manic symptoms — intriguing findings that require replication. (page 223, 226)
Researchers hypothesize that benefits of being in the dark are due to melatonin production by the pineal gland, which occurs when the eyes are deprived of light, as shown during controlled light-dark cycles, even for some blind subjects, indicating that melanopsin is responsible for circadian entrainment in humans.
Bipolar disorder treatment
A single small-scale study done in Hospital San Raffaele of Milan, Italy, concluded that chronobiological interventions and control of environmental stimuli can be a useful add-on for the treatment of acute mania in a hospital setting. Further examinations were done on single patients, and are reported on the link regarding 24-hour biological clocks. A study regarding 48-hour cycles has also been reported.
Circadian rhythm disorders
The circadian rhythm disorders delayed sleep phase disorder and non-24-hour sleep-wake disorder are treated with light therapy upon awakening to suppress the nighttime hormone melatonin. In the hours before bedtime, light restriction and exogenous melatonin may also be used in the attempt to advance sleep phase.
Dark therapy has also been tried (in combination with bright light therapy, etc.) for other conditions where seasonal exacerbation of symptoms are notable, such as nocturnal asthma and associated depression, migraine, dyssomnia, chronic fatigue syndrome and fibromyalgia.
Melatonin secreted is preventative in cancer, and supportive of bone metabolism, immune function and detoxification. Melatonin has also been cited to reduce hypertension, produce better sleep for those with insomnia, and acts as an antioxidant.
By using amber lenses, researchers were able to block blue spectrum light, which affected the "physiology of human circadian rhythm ... suggesting a circadian effect." This effect was previously noted with "amber-tinted safety glasses" which "preserve normal nocturnal melatonin levels in a light environment which otherwise completely suppresses melatonin production."
When having dark hours at home or in a hospital, patients will often be exposed to fewer light-hours per day than in their usual environments, thus requiring a light tight environment. Light from most sources could disrupt dark therapy. Also, it is necessary to have dark therapy hours at specified times during each day in relation to the patient's circadian rhythm.