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- 📉 Why humans are now producing 50% less sleep hormone
📉 Why humans are now producing 50% less sleep hormone
Kevin
February 10, 2024
This week on the Sleepstack Newsletter:
• 🌅 Why leaving behind our ancestral past has disrupted our sleep
• 🧬 Breaking down the giant drop in our sleep hormones
• 🧪 Why light bulbs are really just a big health experiment
🕰️ Disrupted sleep starts with mixed up circadian signals
This 2020 report was one of the top 25 neuroscience papers published in Nature (one of the world’s leading scientific journals) that year. It summarises the main effect of artificial light on healthy adults: melatonin suppression.
Your circadian rhythm is the 24-hour cycle that is responsible for multiple processes throughout the body. It is programmed into nearly every cell, tissue and organ in the body. The paper highlights what happens to our sleep when we interfere with it:
“The most important environmental time cue for the circadian system is light, with the effects mediated primarily by the photopigment melanopsin. In our ancestral past, the circadian system received strong on/off signals, with bright days and dark nights. The availability of electric lighting, coupled with our modern indoor lifestyle, has profoundly changed how humans interact with light. Exposure to light at night suppresses production of the sleep-promoting hormone melatonin and causes circadian disruption, which is associated with a range of poor health outcomes, including disrupted sleep.”
🌑 Where did all the melatonin go?
Most of the effects of evening light-exposure start with melatonin, “the sleep hormone”. Here’s how much melatonin-affecting light (melanopic illuminance) there is in an average home, compared to sunset:
(Cain, S.W., McGlashan, E.M., Vidafar, P.et al. Evening home lighting adversely impacts the circadian system and sleep . Sci Rep 10, 19110 (2020). https://doi.org/10.1038/s41598-020-75622-4)
For most of history there was no blue line on this diagram; after sunset the amount of melatonin-affecting light would have been zero. Night-time lighting creates an artificially-extended twilight.
The result? A dramatic drop in sleep hormone levels, almost halving melatonin production in the average person! Yep, you read that right - halving your sleep hormones:
“Although melanopic illuminance in homes varied greatly, we found that the most sensitive individuals would be highly impacted (> 50% melatonin suppression) by even the dimmest homes. The average home would suppress melatonin by nearly 50% in the average person.”
đź“Š The great light bulb experiment has started producing results
For millennia, our ancestors have fallen asleep to the backdrop of stars. What most people forget is that the light bulb has barely been around for 200 years. In the grand scheme of things, artificial lighting is an incredibly recent experiment.
A huge body of research is now emerging, linking decreasing sleep quality from light exposure at unnatural hours to an diverse range of health implications that include obesity, heart disease and worsening mental health.
Some things are better left in the dark - your sleep is one of them.
Note that fire, which humanity has coexisted alongside for thousands of years, doesn’t seem to trigger any of these effects at all. Fire is part of our “ancestral past”, but the intensity and high-energy wavelengths of artificial light are radically different to anything our ancestors have ever witnessed on a lazy Tuesday evening.
⚡️ Recommendation zone
Actionable insight: invest in blackout curtains, or try a sleep mask
The human eye can detect a single photon of light in a dark room. It’s that sensitive.
Investing in a nice set of blackout curtains can be a game-changer for deep sleep. But I’ve found that a simple sleep mask works wonders for a fraction of the price.
This silk sleep mask is my favourite at the moment.
(I find that the material stays cooler than other variants and doesn’t bother me during the night.)
That’s all for this week!
We’ll be back in your inbox on Saturday,
Kevin
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