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Do Circadian Rhythms effect Lifespans?

  1. Jun 4, 2004 #1
    a lot of research has been done in the field of Circadian Rhythms

    in some experiments human subjects lived for several days isolated from daylight
    with no clocks, and no photoperiodic or environmental clues to indicate time

    the subjects tended to fall into an activity/sleep cycle of 28 hours (100800 seconds) 17% longer than the 24 hour mean solar photoperiod

    strangely no similar test has been done on humans using artificial photoperiods

    rats have been tested under various photoperiods, and it was discovered that the rate of hormonal changes decreased proportionately to the increase in photoperiod


    is it possible that our biological clocks are calibrated to our circadian rhythms?

    could lifespans be extended by living an entire lifetime under an artificial photoperiod?

    if our bodies are programmed to last a given number of days
    creating a longer lifespan is just a matter of extending the day


    if this is the case, the human lifespan could be extended to 150 years
    just by moving society underground and adapting to an artificial photoperiod of 129600 seconds (36 hours) with 43200 seconds of sleep, and 86400 seconds of activity ( 24 hours)

    *it's important to note that lifecycles are set at birth, during the first photoperiod, and are not as easy to change afterward.. full benefits may only be expected in those born underground, but once set.. it should be possible to spend time on the surface without altering the programming

    the increase in productivity, education and progress would be proportional as well, with so much more time to work and study over a longer time

    it would take 30 years to turn 20,
    60 years to turn 40,
    and 90 years to turn 60

    resulting in a much longer period of youth (60 years or more)

    could such a simple change produce such a drastic improvement in human life?
     
    Last edited: Jun 4, 2004
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  3. Jun 5, 2004 #2

    Monique

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    Where did you get that information. Your following statement contradicts that fact :smile:
     
  4. Jun 7, 2004 #3
    at first glance it may seem contradictory

    experimental evidence has shown that the older the subject
    the less prone to lifecycle reprogramming

    there is a difference between circadian cycles and biochemical cycles
    ideally these should be in sync, but during the experiments the cycles diverged

    therefore the statement is not self contradictory

    i am suggesting that subjects living within an extended photoperiod from birth
    will have both cycles in sync, and in effect extend their lifespans
     
    Last edited: Jun 7, 2004
  5. Jun 9, 2004 #4

    Moonbear

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    This article suggests the opposite would be true:

    J Biol Rhythms. 2002 Jun;17(3):210-6.
    *
    Enhanced longevity in tau mutant Syrian hamsters, Mesocricetus auratus.
    Oklejewicz M, Daan S.
    Zoological Laboratory, University of Groningen, the Netherlands.
    The single-gene mutation tau in the Syrian hamster shortens the circadian period by about 20% in the homozygous mutant and simultaneously increases the mass-specific metabolic rate by about 20%. Both effects might be expected to lead to a change in longevity. To test such expectations, the life span of male and female hamsters from three genotypes (wild-type, heterozygous, and homozygous tau mutants, all derived from heterozygote crosses to randomize the genetic background) was recorded in constant darkness. Male hamsters lived significantly longer than females: the overall average life span was 96.9 weeks (SE = 2.5, n = 118) for males and 82.0 weeks (SE = 2.1, n = 99) for females. To our surprise, male and female homozygous mutant hamsters lived significantly longer rather than shorter compared to wild-types. For males, the difference between the two genotypes was on average 14%; for females, the difference was 16%. The mortality rate of wild-type males was significantly different from that of homozygous tau males but not different from that of heterozygotes. Overall, survival of wild-type females was statistically distinguishable from both heterozygous and homozygous mutant females. Male and female wild-type hamsters were heavier than homozygote mutants throughout the entire life span, and heterozygous mutants had intermediate weights. There was no correlation between body mass and life span, and the causes of the extended life span in tau mutant hamsters remain unresolved.

    However, I want to add the caveat I haven't read the full article, just the abstract, so can't verify the methodology for myself (our library doesn't have the electronic version of this journal, so I need to dig up a paper copy from a colleague's office).

    The Tau mutation studied in hamsters is also similar to a mutation present in humans with advanced sleep phase disorder. It also needs to be pointed out that unless you're looking at the actogram of an individual animal, you're usually talking about the population average for circadian rhythms. The endogenous rhythm (the rhythm expressed in the absense of any external cues) varies from individual to individual. It's a little bit "sloppy" because it then becomes entrained, or synchronized, with the external environment, primarily through light cues (but not entirely...in the absence of light cues, other signals can entrain rhythms such as meal times and rhythms of other individuals). This permits the animal to wake up and fall asleep (and hunt, and reproduce, and hide from predators) at the appropriate times of day for that species.

    Also, rhythms are re-entrained during one's lifetime. That's what happens when you get jet lag. You shift your rhythm to the sunrise and sunset of wherever you are. It takes a few days for this to happen (about a week, actually, for most people to fully return to "normal"). So, it's not accurate that your rhythms are set in your first year of life. The entrainment of these rhythms to light begins when the optic nerve reaches a part of the brain called the suprachiasmatic nucleus. In some animals this process is completed in utero, in others, postnatally, depending on how precocial or altricial they are when born.
     
  6. Jun 10, 2004 #5
    this study was not done on subjects born to an extended photo period

    the circadian rhythms of the subjects had already been set to 86400 s prior to the experiment

    it's important to conduct an experiment with subjects born to the test photoperiod and constantly isolated from any other photoperiod
     
  7. Jun 10, 2004 #6

    Monique

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    Ok, so how about people born near the north-/ south-pole circle during winter/summer periods? Those are different photoperiods, ofcourse the day still exists of 24 hours..
     
  8. Jun 10, 2004 #7

    Moonbear

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    Your circadian rhythm is endogenous, determined genetically, not by the environment. The environment only synchronizes that rhythm closer to 24 hours and according to sunrise and sunset, which is also important for seasonality.

    I'm also not sure where you got the information from that humans have a 28 hour free-running rhythm. That's not true. It's about 24.5 hours. If your rhythm was 28 hours, you'd have a serious sleep-disorder. Strange things start to happen when you house animals in photoperiods much different from a 24 hour day/night cycle. The most bizarre is in constant light where mice start to actually split their rhythms. The suprachiasmatic nucleus that controls rhythms is a bilateral nucleus in the brain (in other words, on both sides of the brain). In constant light, something really weird happens such that it appears each side of that nucleus winds up 12 hours out of phase with the other side. If you look at their activity patterns, you can see a splitting so they have two active periods and two resting periods during the day.
     
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