Human circadian clocks couple to local sun time
January 22, 2007By assessing the daily activity patterns of thousands of individuals living in different geographical locations, researchers 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-Universität, 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 over 21,000 individuals living in different geographical locations across Germany. Individuals were compared according to the town size in which they lived: The first group included those in areas with a population size of 300,000 or less, while other groups corresponded to individuals living in towns and cities of larger sizes.
The researchers found that within the first group--individuals in more lightly populated regions--chronotypes were tightly coupled to sun time, while within groups corresponding to more densely populated towns and cities, chronotypes showed a progressively weaker coupling to sun time.
City dwelling potentially impacts the influence of sunlight as a zeitgeber because urban dwellers are typically exposed to less natural light than individuals inhabiting less densely populated areas. The authors propose that the gradual uncoupling of the circadian clock of city dwellers from local sun time may reflect the relative strength of natural-light and social cues in influencing activity patterns. When natural-light cues are more abundant--as seems to be the case in more sparsely populated areas--human circadian rhythm entrains to local sun time.
Past work has indicated that as influences on the circadian clock--known as "zeitgebers"--become weaker, chronotypes tend to become later--that is, daily activity is shifted later in the day. And indeed, the present study found that chronotypes became later with increasing population size.
Source: Cell Press
-
When stars play planetary pinball
Feb 08, 2012 |
4 / 5 (1) |
0
-
STAR TRAK for February 2012
Feb 02, 2012 |
5 / 5 (1) |
0
-
Blue marble 2012: Amazing high definition image of Earth
Jan 26, 2012 |
4.4 / 5 (23) |
14
-
Solar storm sparks dazzling northern lights
Jan 25, 2012 |
5 / 5 (2) |
0
-
Flights rerouted as massive solar storm slams Earth
Jan 25, 2012 |
4.7 / 5 (3) |
0
-
Engineers build first sub-10-nm carbon nanotube transistor
Feb 01, 2012 |
4.9 / 5 (31) |
30
-
Something old, something new: Evolution and the structural divergence of duplicate genes
Jan 31, 2012 |
4.6 / 5 (7) |
1
-
The hidden nanoworld of ice crystals: Revealing the dynamic behavior of quasi-liquid layers
Jan 30, 2012 |
5 / 5 (3) |
1
-
Stock market network reveals investor clustering
Jan 27, 2012 |
3.9 / 5 (23) |
8
-
Of microchemistry and molecules: Electronic microfluidic device synthesizes biocompatible probes
Jan 26, 2012 |
5 / 5 (1) |
0
More news stories
Entire genome of extinct human decoded from fossil
(PhysOrg.com) -- In 2010, Svante Pääbo and his colleagues presented a draft version of the genome from a small fragment of a human finger bone discovered in Denisova Cave in southern Siberia. The ...
Feb 07, 2012 |
4.7 / 5 (58) |
44
|
Why are there so few fish in the Earth's oceans?
(PhysOrg.com) -- A Stony Brook University researcher has found that, contrary to popular belief, there are not plenty of fish in the sea.
Feb 08, 2012 |
4.3 / 5 (17) |
25
|
Miami battling invasion of giant African snails
No one knows how they got there. But an invasion of African giant snails has southern Florida in a panic over potential crop damage, disease and general yuckiness surrounding the slimy gastropods.
Feb 10, 2012 |
4.5 / 5 (2) |
5
The power of estrogen -- male snakes attract other males
A new study has shown that boosting the estrogen levels of male garter snakes causes them to secrete the same pheromones that females use to attract suitors, and turned the males into just about the sexiest ...
Feb 10, 2012 |
4.8 / 5 (6) |
2
|
Deciding to go left or right: Researchers use device to determine that lower animals can navigate too
For decades, scientists have associated binary decision making opting to go left or right with higher-ranking animals, including humans. A team of Harvard researchers, however, is rewriting that ...
Feb 09, 2012 |
4 / 5 (1) |
4
|
Walney offshore wind farm is world's biggest (for now)
(PhysOrg.com) -- The Walney wind farm on the Irish Sea--characterized by high tides, waves and windy weather--officially opened this week. The farm is treated in the press as a very big deal as the Walney ...
GPS court ruling leaves US phone tracking unclear
A US Supreme Court decision requiring a warrant to place a GPS device on the car of a criminal suspect leaves unresolved the bigger issue of police tracking using mobile phones, legal experts say.
Europeans protest controversial Internet pact
Tens of thousands of people marched in protests in more than a dozen European cities Saturday against a controversial anti-online piracy pact that critics say could curtail Internet freedom.
Europe stakes billion-dollar bet on new rocket
A pencil-slim rocket is scheduled to lift into space from South America on Monday, carrying a billion-dollar bet that Europe can grab a juicy slice of the market to place satellites in low orbit.
Study finds that anti-diabetic medication can prevent the long-term effects of maternal obesity
In a study to be presented today at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in Dallas, Texas, researchers will report findings that show that short therapy with the anti-diabetic medication ...
Netflix settlement trims 14 pct off 4Q earnings
(AP) -- Netflix pressed the rewind button on its fourth-quarter earnings after settling allegations that the video subscription service violated a consumer-privacy law.