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Comment by randallsquared | Hacker News Reader

By the age of 30 you should definitely be able to know what your needs are.

Well, except that it was around 30 that my needs started changing. Until then I often needed 8-9 hours a day of sleep, but sometime after 30 I noticed that I wasn't sleeping as long (and I'd long been out of the habit of using an alarm clock until last year, because I worked for myself and never scheduled anything in the early morning). Now my average is more like 7 hours a day, and it's not uncommon for me to wake up after 5 or 6 hours feeling just as rested as I used to after 9.

Talking about sleep schedules with my father led to the interesting revelation that this happened to him about my age, and it continued decreasing right along, so that now, in his 80s, he's only sleeping about 4 hours a night, and doesn't feel that he needs more. So, I guess I've got that to look forward to. :)

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You are absolutely right that sleep pattern (and in fact sleep architecture as well) changes with age. Sleep needs tends to decrease with age.

30y is pretty much the time when you enter into your "adult phase" that will last for the next 30 years or so.

Do you have any insight on the role that sleep plays in the aging process?

If we're able to get less good sleep as we age, and sleep is essential for mental acuity (forming memories, etc) and for physical health (growth hormone, etc), i've long wondered if the two are related.

The truth is that we still have no whatsoever idea of what sleep is for, to start with. There are hypothesis out there but none of them is even close to be considered scientifically plausible.

Some of them say sleep has something to do with maintaining a plausible number of neuronal connections (synapses) in your brain: the more you learn and do during the day, the more synapses you build, the more sleep you need to clean up for the next day. As you age, your brain plasticity decreases, i.e. the ability for your brain to change the number of synapses is not as good. This is why you might need less sleep than when you were a young kid.

If you are interested in the topic, I'd suggest to have a look here: http://thesciencenetwork.org/programs/waking-up-to-sleep Some of the talks can be of interest to the general reader. The Science Network is a very good source of good-quality easy to access scientific material.

I'm 17, so that's not only less than thirty but also less than what most people consider 'adult' at all.

Is screwing with my sleep cycle a bad idea at this age? Or is age irrelevant? Biphasic sleep especially sounds attractive to me, but I do not know whether it would be healthy to try.

Given that you are a sleep researcher, I was hoping perhaps you could provide some insight?

Well, I wouldn't recommend it. A bad sleep hygiene in pre- and adolescent kids (especially pre-) is known to associate with obesity, hypertension and diabetes - there is quite a great deal of literature on that.

At your age your sleep pattern is already pretty much messed up by itself (you may already find yourself working late at night and having big sleep inertia in the morning) and I wouldn't complicate things any further.

There was a kid exactly your age who in 1964 decided to establish the world record for sleep deprivation. http://en.wikipedia.org/wiki/Randy_Gardner_(record_holder) He went on for 11 days and he was supported by a physician all the time. This was back in the days when we still didn't know sleep deprivation was lethal in rats.

no whatsoever idea of what sleep is for

I thought it was clear from looking at other animals that a large part of the value of sleep relates to saving energy. Animals that do something like sleep while staying awake burn more energy but don't drown / get eaten as much which makes up for that. Granted, there is other things that happen as part of sleep, but saying we have no idea when some things are fairly well known seems to be over the top.

The "saving energy" idea was out in the 80's, mainly put forward by Rechtschaffen and colleagues but it was abandoned the moment people realized that a sleeping brain does not consume much less energy than the awake brain. In fact the energy consumption during REM is identical to during wakefulness (REM sleep is called also paradoxical sleep because the EEG looks very very similar to a fully working brain), and energy consumption during NREM is about 10% less than awake - absolutely not enough to justify evolutionary the need for sleep. The amount of energy that you save with one night of sleep is estimated to be bit less than one frankfurter bun.

After centuries of interest we still don't know why we sleep. We have no idea, really. We know rats die if you sleep deprive them for long enough (between 10-30 days) but we don't know what they die of. I work with fruitflies myself and investigating sleep function is what I am trying to do.

I did not mean to suggest that the only reason for sleep was saving energy. But, the duration of sleep relates to the option to sleep that long while getting enough food, and not being eaten.

The human body saves a lot more energy than one frankfurter bun though sleep by simply not moving all that much. Clearly the brain and body are doing something useful while you sleep, but if it needs to do that stuff and walk around / be awake at the same time it would use even more energy.

Bats, sleep 18-20 hours per day vs. giraffes which sleep 3-4 hours per day etc.

PS: REM sleep is another issue, but the differences in human sleep cycles suggest that sleeping less is not the only goal.

The human body saves a lot more energy than one frankfurter bun though sleep by simply not moving all that much [...] Bats, sleep 18-20 hours per day vs. giraffes which sleep 3-4 hours per day etc.

I see. I think what you are talking about is not even energy expenditure but what we call "the null hypothesis". Basically says that there might be no other active function than sleep other than resting as a mean to escape predators and not using energy. This is far from being the accepted hypothesis on sleep function: in fact there is basically only one guy who still talks about this (Jerome Siegel, UCLA); the rest of the community is pretty much convinced that this is not the case. I'd suggest you reading this on the matter: http://www.plosbiology.org/article/info:doi/10.1371/journal.... (it is open access).

I think we are talking past each other. I suspect sleep does a lot of useful things. Just as humans lost the ability to produce vitamin C we may have become dependent on sleep for things that are not required in theory. So there may be layers of dependence that show up over time. My suggestion is talking about what sleep does can be separated from the fact that sleep is so common and needed.

PS: Your liver does many things necessary for you to live. It also does many things that help you live a better life. Talking about what your liver or sleep does, without including the useful side effects is not the full story. Sleep deprivation hinders memory formation in humans and hinders reaction times. Are those related to the core function of sleep or just a codependence developed due to other useful features of sleep? I don’t think there is a clear separation between the two.

Edit: I can't read that link.

As an observer, I appreciate the debate, and I'll add that it doesn't seem to me like you're talking past each other. Giving the other gentlemen the benefit of the doubt that he's something of an expert on this subject, it seems he's very clearly understanding your point and offering his opinion to the contrary.

I, myself, have nothing much to add in the way of hard facts, but using logic, I think that sleep-as-an-energy-saver seems off. Sleep seems like a highly vulnerable state for early animals. If the only initial benefit of sleep was energy conservation, it seems like animals that simply chose to rest would have an edge upon those that slept. By resting, they'd conserve the same energy, but would stay alert and responsive.

And it interests me that animals that cannot rest (sharks, for example) still sleep.

If I am not mistaken, that's common for everybody.

Older people seem to need less sleep.

Then again, perhaps old age just means you can't get more then x hours of continuous sleep.

Maybe it's because metabolism slows down and so you don't need as much sleep to 'recover' from the day?

I think I've got the exact same sleep genetics as you do.

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