{'fraction_non_alphanumeric': 0.030476873431337398, 'fraction_numerical': 0.02832556471853711, 'mean_word_length': 5.21380846325167, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 1, 'xml': 0}, 'pii_count': 1, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 1, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Melatonin and the body clock

Melatonin and the body clock Josephine Arendt* and Benita Middleton Centre for Chronobiology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK (Received 10 March 2007; final version received 29 January 2008) The pineal hormone melatonin, via its secretion pattern during the hours of darkness, is the only solidly established humoral method of signalling time of day and time of year to other physiological systems. Melatonin is also of great importance for research on the physiology and pathology of the human biological clock. Its profile in plasma or saliva provides the best available measure of circadian timing, of response to changing daylength and of non-image forming responses to ocular light. Its primary metabolite, 6sulphatoxymelatonin, in urine allows long-term monitoring of human rhythms in ‘‘real life’’ situations where rhythms may be disturbed. Melatonin is not only a ‘‘hand of the clock’’: endogenous melatonin acts to reinforce the functioning of the human circadian system, probably in many ways. Most is known about its relationship to sleep and the decline in core body temperature at night. Current perspectives also include a possible influence on major disease risk, arising from circadian rhythm disruption. Treatment with melatonin induces sleepiness and lowers core body temperature during ‘‘biological day’’ (when endogenous melatonin is low) and the timing (phase) of human rhythms can be changed when treatment is appropriately timed. Melatonin is able to entrain free running rhythms and maintain entrainment in most blind and some sighted people. Used therapeutically it has proved a successful treatment for circadian rhythm disorder, particularly the non-24 h sleep–wake disorder of the blind and delayed sleep phase syndrome. Less consistent results have been found for the problems of shift work and jet lag. Correct timing of treatment relative to internal clock time is very important and often not appreciated. Variable individual responses to time zone change and shift work mean that correct timing of treatment is difficult. Numerous other clinical applications are under investigation. However areas of controversy and large gaps in knowledge mean that general conclusions cannot be drawn with regard to most situations. The future holds much promise for melatonin as a research tool and as a therapeutic treatment. Reproduced in part with permission from Arendt J. 2005. Melatonin: characteristics, concerns and prospects. J. Biol Rhythms. 20:291–303. *Corresponding author. Email: arendtjo@aol.com Biological Rhythm Research Vol. 40, No. 1, February 2009, 81 ISSN 0929-1016 print/ISSN 1744-4179 online 2009 Taylor & Francis DOI: 10.1080/09291010802067114 http://www.informaworld.com