4-5 hours is adequate for many people. Myself being one of them. I don't take any uppers besides coffee and find 4-5 is ideal and 6-7 makes me groggy if I can even accomplish that. Usually after 5 hours of sleep I wake up with no alarm clock wide awake.

Do you also run 8-12 miles every day at a sub 8 minute pace, run a fledgling technology company, and have a new born child?

Well, even if you don't, you're still damn lucky to have that kind of energy.

no, but I am a co-founder of a fitness startup, and try to get a lot of exercise! 8-12 miles is more than I do, and I do not have a kid.

I'm pretty intrigued by anyone who can honestly perform on 4-5 hours of sleep, night after night after night.

To what do you attribute this ability? Have you always been a short-sleeper? Is it something you've worked toward? Is age a factor? Diet?

I'm not sure if ability is the right word but maybe?

I know several people like this, my gut tells me it's not super uncommon.

It was not always like this , but the older I get the less sleep I seem to need. In my 20s would feel groggy on 5 hours of sleep, but in my 30s ( current age ) I feel groggy if I get more than 5 hours sleep.

I haven't been able to "sleep in" since I was probably 15 or 16.

Some people probably call this being a morning person, to over simplify it heavily.

Edit: if you do some light googling there is a substantial anoint of data on the internet that claims 8 hours of sleep is too much and 6 is closer to ideal for full grown adults. So getting 4-5 and a healthy dose of exercise does not seem in the realm of supernatural to me. Give it a shot! ( don't leave out the exercise either )

Well, I would describe your inability to sleep in, as definitely qualifying for being a morning person.

On the other end of the spectrum, you have individuals like myself. From my teens into my early twenties, my ideal sleep cycle was 4am to 1:00pm. Probably still would be my ideal sleep cycle, if that fit into civilization.

It's hilarious to think I could maybe survive on 5 hours. Go to sleep at 4, wake up at 9? Hah, ya right.

4-5 hours of sleep as a typical habit isn't that rare, unfortunately.

I guess I don't understand how that's sustainable. I can do it for a couple of days, maybe a week. Beyond that, and my performance both physically and mentally takes a large hit. I guess it's possible that some people are blessed with super-human energy levels. It's more likely that they're on something.

The real question though is whether this affects their memory, reflexes and immune system. Former is reasonably simple to test, latter requires a longer study. The problem is placebo control, which of impossible, and required monitoring to detect microsleeps and oversleeping.

You would need a control group, group with day, forced 8h sleep both biphasic and monophasic, and a group on this fancy multiphasic schedule.

Expensive to run.

Well, peoples' need for sleep does vary, but I do suspect it affects them, whether they know it or not. Caffeine is a hell of a drug too.