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Comment by slothtrop | Hacker News Reader

Add to the fact, adherence to a fixed advanced sleep/wake schedule can lead to significant circadian phase shifts in adults with DSPD -- https://www.sciencedirect.com/science/article/abs/pii/S13899...

People are downplaying the extent to which habits and preferences have an impact. Staying in bed late will shift forward your circadian rhythm. Blue-light emitting electronics will suppress melatonin at night and raise cortisol.

Before the industrial revolution few were staying up all night regularly unless they were on night shift. Bright light and multimedia available at night changed.

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People also used to wake up at 1, stay awake for a couple hours, and then go back to sleep.

https://www.sciencealert.com/humans-used-to-sleep-in-two-shi...

> Add to the fact, adherence to a fixed advanced sleep/wake schedule can lead to significant circadian phase shifts in adults with DSPD

This statement is not supported by your link:

> 25 adults...with late sleep schedules and subclinical features of delayed sleep phase disorder (DSPD).

The "subclinical features" part is important! I am not trying to step into the "habits versus nature" part for healthy night owls / morning larks, but actual clinical DPSD is a significant medical problem that is very clearly not related to habits or sleep hygiene. Which means comments like this:

> Before the industrial revolution few were staying up all night regularly unless they were on night shift. Bright light and multimedia available at night changed.

are truly irrelevant here, and inappropriately judgmental of people with a real illness.

Wasn't the whole blue light thing disproved about a year ago? IIRC more light late at night disrupts the cycle, but the color of it was irrelevant.

According to research I've found, red light will raise cortisol but not suppress melatonin production. Blue light does both. Don't remember which paper, but I found this one suggesting that blue light is worse than regular white light (which includes the blue spectrum) at suppressing melatonin: https://onlinelibrary.wiley.com/doi/abs/10.1034/j.1600-079X....

If I'm not mistaken, that was research in mice. Mice are nocturnal and do not likely have the same entrainment patterns with respect to blue (sky) light.

There are still valuable things that can be learned from that kind of research, but the popular coverage really missed the mark by directly extrapolating from research in mice to human circadian rhythms.

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