Researchers, by assessing the daily activity patterns of thousands of individuals living in different geographical locations, have found evidence that the human circadian// clock becomes coupled to so-called local sun time despite the fact that people live and work according to a common "social time" that is determined by time zones.
The work also indicated that city dwellers appear to experience a relatively decreased influence of local sun time relative to those living in more sparsely populated areas. The findings appear in the January 23rd issue of Current Biology and are reported by Till Roenneberg of Ludwig-Maximilians-Universit?t, Germany; C. Jairaj Kumar, of Kasturba Medical College, India; and Martha Merrow, of the University of Groningen, in The Netherlands.
Because our watches and clocks are set according to time zones, which are constant over multiple longitudes, rather than according to local sun time, which continuously changes across longitudes, there is often a discrepancy between the natural-light cues one receives as a result of local sun time and the "social" cues one receives as a result of clock time. The extent of such discrepancies depends on the time of year and one's location within a time zone, but can be substantial: In some cities, midnight (according to clock time) can fall well beyond an hour away from "mid-dark."
The relative influences of these two types of cues on circadian rhythms are not fully understood by scientists, and in the new work, researchers sought to address this issue by comparing the circadian behaviors of people experiencing these influences to different extents in their daily lives.
The measure used to assess patterns of daily activity is the so-called chronotype, which is determined by answers to questionnaires that assess patterns of habitual activity and rest during work days and free time.
In the present study, the authors compared the chronotypes of oPage: 1 2 Related medicine news :1
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