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Melanopsin = Melatonin = Sleep


Our obsession with sleep driving explosive growth in the melatonin market – $2.5 billion, growing at annual rate 14.5% – Melatonin Supplements Market Size.

Our investment in drugs that promise to help us to snooze seems reasonable given cost of poor sleep in financial and economic terms: 10.3% productivity loss, adding up to $136billion estimated cost to US economy in 2022 – Sleep & Workplace Productivity: The High Cost of Lost Sleep to the Workplace.
Improving sleep boosts quality of life on every measure, from pain to energy levels and mood – 
Improved Sleep Quality is Associated with Reductions in Depression and PTSD Arousal Symptoms and Increases in IGF-1 Concentrations.

Our faith in melatonin is driven by a belief in a simple three-stage chain reaction that links

Melanopic lux (response to light weighted to peak sensitivity of melanopsin in ipRGCs – sky blue 480nm)  Human-Centric Lighting: Foundational Considerations and a Five-Step Design Process.


Melatonin levels (dim light is a trigger for increased melatonin production, hence Dim Light Melatonin Onset)

And from there to…

Sleep – (various measures including sleep latency or how long it takes you to get to sleep, time in different stages of sleep, e.g. REM, and subjective measures such as how sleepy you feel, the Karolinska Sleepiness Scale)

But when you look more closely at the data, the 50-fold difference in melatonin response to light after dark between healthy adults – High sensitivity and interindividual variability in the response of the human circadian system to evening lightand other studies that show melatonin may be no more effective than placebo – Does Exogenous Melatonin Improve Day Sleep or Night Alertness in Emergency Physicians Working Night Shifts? suggests a more complex link that light and health professionals need to consider if we want to get a good nights’ sleep.

One obvious contributing factor to this range is age: older eyes become cloudy and yellow, filtering out many of those ‘wake-up’ blue wavelengths. While the melatonin response to all bright light is indeed much lower in older adults in the first 15 to 30 minutes of exposure, by the 60-minute mark, the short wavelength cones seem to kick in.  Over longer durations, the response to short wavelength (red) light (>500nm) similar in young and old – Aging of Non-Visual Spectral Sensitivity to Light in Humans: Compensatory Mechanisms?,  Aging, light sensitivity and circadian healthPerhaps that may help to explain why full spectrum light seems to improve the quality of sleep, – Effect of daylight LED on visual comfort, melatonin, mood, waking performance and sleep.

Another contributing factor may be the dynamic quality of the light itself. One study compared a windowless control room with a test room that combined daylight with dynamic lighting. Despite similar melanopic lux in both settings, the experimental setting ‘promoted earlier melatonin onset and peripheral heat loss prior to bedtime.’ – Optimized office lighting advances melatonin phase and peripheral heat loss prior bedtimeThis builds on earlier research that demonstrated that windows not only improved sleep, but increased physical activity too – Impact of Windows and Daylight Exposure on Overall Health and Sleep Quality of Office Workers: A Case-Control Pilot Study.

This points to the critical psychological dimension in circadian entrainment. One paper found that, although there was no significant correlation between illuminance level and dim light melatonin onset (DLM0), there was a clear link between between colour temperature of light and DLMO. The team concludes:  high color temperature light at home might be a cause of the delay of circadian phase in adults and children – The effects of light in children: A systematic review.

Even if popping a melatonin pill were the secret to a good nights’ sleep, there is currently no approved dose, with some physicians warning of significant side-effects of high doses or sustained use over time – Current Insights into the Risks of Using Melatonin as a Treatment for Sleep Disorders in Older AdultsThe same paper notes a shocking variation in the formulation of these over the counter drugs: measured content of −83% to +478% of the labeled melatonin dose.

Perhaps it’s time to take another look at the melanopsin-melatonin equation and spend our hard-earned cash on spaces that provide the rich, dynamic clock-setting cycle of light and darkness we need to drift off to the land of nod.


Melatonin in your earbuds with Dr. Christine Blume

The Sleep Research Society hosts an excellent podcast with interviews with brilliant scientists talking about their background and a recent paper – This one features Dr. Christine Blume talking about her brilliant work that challenges the link between melatonin and sleep – SRS PODCAST (#7): Melatonin suppression does not automatically alter sleepiness, vigilance, sensory processing, or sleep.


Melatonin and circadian swimming

While you and I are falling into a deep sleep, Invertebrates such as plankton and some fishes are swimming silently to the surface under cover of darkness, only to fall back to the dark depths during the day. This ancient cycle, known as diel vertical migration (or DVM) evolved to protect these delicate organisms against sun damage. This fascinating paper draws a direct link between this circadian swimming response and the mammalian sleep-wake cycle and explains how melatonin became the signal of darkness – Melatonin Signaling Controls Circadian Swimming Behavior in Marine Zooplankton.

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