Is the observed age-related trend caused by a decrease in sleep capcity?
It is not easy to answer...
Soma authors did not found any response or even a delay.
I think that there are two posible main reasons if we assume the phase advance:
1. Maybe because their exposure is only in the morning and their afternoon and evening are really dark.
2. Perhaps because the tau is shorter in elderly.
But, authors that described those changes used cosinor analysis. Which have a problem because the assumption of a sinusoid. Now, I am working on data from elderly people and I think that they have and advance during daytime due to the light exposure that I mentioned in 1 but not during nightime (maybe because of TV).
At least it is my impression from Spanish elderly people
"Soma authors did not found any response or even a delay."
Phase of sleep episode always tend to advance with advancing age.
"1. Maybe because their exposure is only in the morning and their afternoon and evening are really dark."
Any evidence? Light exposure can be controled. Imagine that someone lived all his life in the same house and under the same level and pattern of illumination. How about his phase of sleep episode? Does it exhibit an advance with advancing age?
"2. Perhaps because the tau is shorter in elderly."
I m also wondering about this.
About your first sentence, I have some non-published data against the phase advance of sleep phase in elderly. I found an advance in the activity phase but not in the sleep phase for sleep or activity.
Regarding your second sentece, there are few papers about lught exposure and even less in elderly people (I do not remember anyone). But you have papers about actigraphy and you can see that they are more active during mornings and it could be because they go shopping or for a walk and then during afternoons or evenings they are more inactive. But I am working now in these data about elderly and they have more light exposure during mornings. If you want I can send you the paper when it will be published (If I get it).
Tau is always the first posibility, but if tau changes and they are exposed to bright light during late afternoon they could be phase stable.
Thank you for your response
" I have some non-published against the phase advance of sleep phase in elderly. I found an advance in the activity phase but not in the sleep phase for sleep or activity. " You must publish it, since this is something definitely new: Older people are shifted toward morningness this means they have advanced sleep episode.
"they are more active during mornings and it could be because they go shopping or for a walk and then during afternoons or evenings they are more inactive." The question is: why they are more active during monings.
Yes, you are right. The question is that, but I do not know the complete answer. Maybe in another experiment.
Thank you for your response
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