Dark therapy, also called scototherapy, light restriction and darkness therapy, is a treatment which involves eliminating all light, or all blue light, in a subject's environment, for a period of several hours prior to bedtime. Dark therapy manipulates the 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.
Circadian rhythm disorders
Humans are diurnal, sleeping at night. Many physiological processes proceed in 24-hour cycles each day, coordinated by the environmental daylight/darkness cycle in nature. People with circadian rhythm disorders do not have the normal relationship to this daily cycle. Their bodily processes may, or sometimes may not, be well-synchronized with each other, but they are not correctly synchronized with the light/dark cycle. Examples are delayed sleep phase disorder, where sleep timing is delayed several hours, and non-24-hour sleep-wake disorder, where the circadian period is longer or, very rarely, shorter than the human average of 24.2 hours.
Sleep timing is regulated by the hormone melatonin, produced in the brain before sleepiness occurs and during the night. It is almost undetectable in the blood during daytime. Recommended treatments for circadian rhythm disorders are light therapy and dark therapy. For the disorders mentioned above, bright light to the eyes upon awakening to suppress melatonin and light restriction in the hours before bedtime to encourage production of the hormone are recommended. Darkness therapy does not require total darkness. Melatonin is suppressed by blue light, principally around 460 to 480 nm. Amber colored goggles eliminate blue light to the eye while allowing vision. The best timing of the two therapies must be individually determined.
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.
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, fibromyalgia and seasonal affective disorder (SAD).
Melatonin 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 glasses or goggles, 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."
- Wirz-Justice A (2005). "Chronobiological strategies for unmet needs in the treatment of depression" (PDF). Medicographia 27 (3): 223–7.
- Skene, D.J.; Arendt, J. (September 2006). "Human circadian rhythms: physiological and therapeutic relevance of light and melatonin". Ann. Clin. Biochem. 43 (Pt 5): 344–53. doi:10.1258/000456306778520142. PMID 17022876.
- Macchi, M.M.; Bruce, J.N. (2004). "Human pineal physiology and functional significance of melatonin". Front Neuroendocrinol 25 (3–4): 177–95. doi:10.1016/j.yfrne.2004.08.001. PMID 15589268.
- Silva, M.M.; Albuquerque, A.M.; Araujo, J.F. (September 2005). "Light-dark cycle synchronization of circadian rhythm in blind primates". J Circadian Rhythms 3 (1): 10. doi:10.1186/1740-3391-3-10. PMC 1208936. PMID 16144547.
- Brainard GC, Hanifin JP, Greeson JM, Byrne B, Glickman G, Gerner E, Rollag MD (August 2001). "Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor". J. Neurosci. 21 (16): 6405–12. PMID 11487664.
- Barbini, B.; Benedetti, F.; Colombo, C.; Dotoli, D.; Bernasconi, A.; Cigala-Fulgosi, M.; Florita, M.; Smeraldi, E. (February 2005). "Dark therapy for mania: a pilot study". Bipolar Disord 7 (1): 98–101. doi:10.1111/j.1399-5618.2004.00166.x. PMID 15654938.
- Biological Clocks and Bipolar Disorder
- Voderholzer, U.; Weske, G.; Ecker, S.; Riemann, D.; Gann, H.; Berger, M. (2002). "Neurobiological findings before and during successful lithium therapy of a patient with 48-hour rapid-cycling bipolar disorder". Neuropsychobiology 45 (Suppl 1): 13–9. doi:10.1159/000049256. PMID 11893872.
- Durlach, J.; Pagès, N.; Bac, P.; Bara, M.; Guiet-Bara, A. (March 2005). "Magnesium depletion with hypo- or hyper- function of the biological clock may be involved in chronopathological forms of asthma". Magnes Res 18 (1): 19–34. PMID 15945613.
- Witt-Enderby, P.A.; Radio, N.M.; Doctor, J.S.; Davis, V.L. (November 2006). "Therapeutic treatments potentially mediated by melatonin receptors: potential clinical uses in the prevention of osteoporosis, cancer and as an adjuvant therapy". J. Pineal Res. 41 (4): 297–305. doi:10.1111/j.1600-079X.2006.00369.x. PMID 17014686.
- Phelps, J. (2008). "Dark therapy for bipolar disorder using amber lenses for blue light blockade". Med. Hypotheses 70 (2): 224–9. doi:10.1016/j.mehy.2007.05.026. PMID 17637502.