The Living Thing / Notebooks :

Sleep; pathologies and hacks

Things about 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).