Things about sleep.
Do we sleep enough?
The photogenic researcher who keeps on making pronouncements about the pathologies of modern work schedules, and whose name I can never remember is Till Roenneberg. He is attached to the EUCLOCK project, and the MPG and LMU etc. I’m not convinced, BTW, by the Munich Chronotype Questionaire due to him and Martha Merrow; the questions make almost no sense for my own personal routine, so I wonder who else they cover poorly? However, the strident lifestyle advice that these folks give out rests on more data than that particular survey, as far as I can tell.
If you take one thing away from this entire essay, remember this: as long as you feel good, sleeping anywhere between 5 and 8 hours a night seems basically fine for your health (see Section 1), regardless of whatever Big Sleep wants you to believe.
All of the evidence we have about sleep and long-term health is in the form of those essentially meaningless correlational studies, but if you’re going to use bad science to guide your sleep habits, at least use accurate bad science.
Why do we sleep?
We have known for quite awhile now that light is the most powerful cue for shifting the phase or resetting the time of the circadian clock. We also know that melatonin is present at low levels during the day, begins being released a few hours before bedtime and peaks in the middle of the night. Past studies have shown that light suppresses melatonin, such that light in the early evening causes a circadian delay, or resets the clock to a later schedule; and light in the early morning causes a circadian advancement, or resets the clock to an earlier schedule. […] we found that humans display a peak sensitivity to light in the blue wavelength region of the spectrum. Rods and cones […] could not account for this differential regulation of melatonin production, so we postulated another type of photoreceptor was responsible for mediating such physiological responses. These wavelength-sensitive photoreceptors were identified soon after and are known as melanopsin-containing ganglion cells
The 2005 meta-analysis Brzezinski et al concluded that, over all (mostly healthy) adult participants, melatonin improved on placebo to the extent that it [statistically-]significantly reduced sleep onset latency by 4.0 min (95% CI 2.5-5.4) [The normal limits for latency to sleep are considered to be 15-20 min.]; increased sleep efficiency by 2.2% (95% CI 0.2-4.2) [The normal sleep efficiency is about 90-95%.], and increased total sleep duration by 12.8 min (95% CI 2.9-22.8). […] One might object that they do not wish to tamper with their natural sleep, even if melatonin is a normally-secreted hormone. Sad to say, I would point out to such readers that they are already profoundly tampering with their natural sleep cycle, and indeed, all of Western civilization is tampering with it; most of my readers do not even sleep multiple times during the day, as Nature intends and as humans have usually slept through history […]
So if you want to go to sleep (and wake up) earlier, you want to take melatonin early in the day. How early? Van Geijlswijk et al sums up the research as saying it is most effective “5 hours prior to both the traditionally determined [dim light melatonin onset] (circadian time 9)”. If you don’t know your own melatonin cycle, your best bet is to take it 9 hours after you wake up (which is presumably about seven hours before you go to sleep).