xxvii. Two Japanese studies

14 June 2006 at 13:31 | Posted in Circadian rhythm | 6 Comments
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Those of us who can, reset our body clocks daily. The primary cue from the environment is light. The vast majority of us need to advance our phase, that is, shorten our built-in day to match the light/dark cycle in nature. This is what normal people do so easily.  

By definition, people with Delayed Sleep-Phase Syndrome (DSPS) can adjust to a 24 hour day, even though they don’t fall asleep before 2-6 a.m. or even later. People with Non-24-hour Sleep-Wake Syndrome cannot of their own accord.  

M. Uchiyama et al in Japan have studied Non-24 and DSPS people, comparing both with normal controls and with each other. The following table is constructed from two of their reports, published in 2000 and 2002. No blind subjects were included in these two studies. 

* Both the Non-24 and the DSPS people slept longer than the normal ones.

* Non-24 people had a short interval from sleep onset to the melatonin midpoint.

* Both Non-24 and DSPS people had a long interval from the core body temperature trough (nadir) to wake-up.

* DSPS people had a longer interval between sleep onset and nadir than Non-24 people.

 We know that normal people are exposed to morning light about two hours after nadir, as that is their “hard-coded” wake-up time. Light exposure is less and less effective in resetting the body clock in the hours which follow. 

Core body temperature is one marker of an individual’s circadian period.

In the table above, which shows an approximation of the intervals reported, one can see that when DSPS and Non-24 people are allowed to awaken spontaneously, their earliest light exposure occurs much more than the normal two hours after nadir. 

The Japanese researchers conclude that the lack of light two hours after nadir hinders a normal adjustment of the circadian pacemaker. They also postulate that a delayed sleep onset relative to one’s own pacemaker allows for an accelerated light-induced phase-delay. As they put it, “We postulate these alterations in phase relation to be associated with phase changes of the circadian pacemaker via different illumination timings.” 

Non-24 patients have a significantly more faulty phase angle between sleep onset and the circadian pacemaker than DSPS patients have.

Uchiyama M, Okawa M, Shibui K, Kim K, Tagaya H, Kudo Y, Kamei Y, Hayakawa T, Urata J, Takahashi K. Altered phase relation between sleep timing and core body temperature rhythm in delayed sleep phase syndrome and non-24-hour sleep-wake syndrome in humans. Neurosci Lett. 2000 Nov 17;294(2):101-4.

Shibui K, Uchiyama M, Okawa M. Melatonin rhythms in delayed sleep phase syndrome. J Biol Rhythms. 1999 Feb;14(1):72-6.

Okawa M, Uchiyama M. Circadian rhythm sleep disorders: characteristics and entrainment pathology in delayed sleep phase and non-24-h sleep-wake syndrome. Sleep Med Rev. 2007 Dec;11(6):485-96. Epub 2007 Oct 25.

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Next:  xxviii. Some good news

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6 Comments »

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  1. Quote: “The Japanese researchers conclude that the lack of light two hours after nadir hinders a normal adjustment of the circadian pacemaker.”

    So what would happen if we would be able to determine our nadir and then automatically switch on our special lights 2 hours after this point while we are still sleeping? Did anyone experiment with this so far, just wondering whether this might be helpful?

  2. Yes, I do know of a teenager with Non-24 who was treated at Johns Hopkins and Kennedy Kreuger(sp?). He was well-studied and even so the use of morning light required some trial and error. IIRC, the timing which worked was from 15-30 minutes before wake-up. I’ll see if I can find an account of that online.

  3. Thanks for looking into this, fortunately I am not suffering from N24 so I am not sure whether this will help me much.
    .
    And about this Japanese study I have a problem with the following statements:
    .
    1. “We know that normal people are exposed to morning light about two hours after nadir, as that is their “hard-coded” wake-up time.”
    .
    This hard-coded wake-up time might be the cortisol production that kicks in which is around 2 hours before waking up which coincidentally is at the same moment of nadir. They also state that the time between nadir and wakeup in DSPS takes a lot longer for DSPS, so once again, maybe the cortisol production does not happen as it is supposed to with DSPS?
    .
    .
    2. “The Japanese researchers conclude that the lack of light two hours after nadir hinders a normal adjustment of the circadian pacemaker.”
    .
    I do not see why adjusting the circadian pacemaker for regular DSPS people wouldn’t work as they can retain a 24h schedule if they can sleep/wake up at their (own) preferred time. In addition, they will fall asleep/wake up around the same time every day, which suggests to me that they do in fact reset their circadian pacemaker on a daily basis otherwise sleep/wake times would drift as with N24 people.
    .
    And one last remark, cortisol production is also regulated by light, although it does respond to any type of light (daylight + any artificial type of light), while melatonin production only responds to daylight!

  4. Melatonin production does respond to artificial light as well as daylight. Else no one would use bright light therapy. Also many with DSPS work hard to avoid indoor light (with blue in it) the hours before bedtime.

  5. Thanks for correcting me on this… I came across an article about Cortisol where they made this statement. Now it seems that this is not correct. Is it correct to assume that Melatonin only responds to blue light? If so, then artificial light might also contain some blue light, also the reason why light boxes are recommended for the treatment of DSPS, correct? Now I start to wonder whether Cortisol also responds the same way (blue only) or to any type of lightning? Seems like I have to do dome additional research… Aside of this, I am still convinced that there is a connection between DSPS & Cortisol…

  6. It’s blue light and part of the green range which excites the light sensitive ganglion cells in the retina and banish melatonin production. The strongest effect is at about 480 nm (blue). It seems, intuitively, that the relationships between melatonin rhythm, body temperature rhythm and cortisol rhythm are important, but I know little about that.


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