Summary
This review challenges the traditional pineal-centric view of melatonin by identifying four distinct melatonin sources — pineal, extrapineal, microbiota, and dietary — each with different regulatory mechanisms, including stimulation by near-infrared light rather than suppression. For lighting designers and healthcare practitioners, this suggests that non-visible solar radiation (NIR) may have meaningful physiological effects on melatonin and cellular homeostasis that are not captured by current visible-light-focused lighting standards.
Key Findings
- At least four sources of melatonin exist in vertebrates: pineal gland, extrapineal tissues, microbiota (skin, gut, mouth, nose, vagina), and dietary melatonin.
- Unlike pineal melatonin (suppressed by visible light), extrapineal melatonin levels can increase during heavy exercise in daylight containing NIR radiation, elevating sweat and potentially plasma melatonin concentrations.
- Extrapineal melatonin production capacity is proposed to far exceed that of the pineal gland, serving rapid ROS-scavenging and intercellular homeostasis functions.
- High levels of melanopsin have been discovered in most fat (adipose) cells, suggesting light responsiveness extends well beyond retinal photoreceptors and challenges pineal-centric circadian theories.
- Near-infrared light is proposed as a regulator of extrapineal melatonin synthesis, with potential implications for therapeutic NIR light exposure strategies.
Categories
The Science of Light: Examines how near-infrared light (NIR) regulates extrapineal melatonin synthesis and the role of melanopsin in fat cells, expanding understanding of photoreceptor biology beyond retinal pathways.
Sleep & Circadian Health: Discusses the role of multiple melatonin sources in circadian and photoperiodic regulation, challenging the pineal-centric model of melatonin-driven light/dark cycles.
Author(s)
DX Tan, RJ Reiter, S Zimmerman, R Hardeland
Publication Year
2023
Number of Citations
17
Related Publications
The Science of Light
- Phototransduction by retinal ganglion cells that set the circadian clock
- Color appearance models
- The mammalian circadian timing system: organization and coordination of central and peripheral clocks
- Diminished pupillary light reflex at high irradiances in melanopsin-knockout mice
- Melanopsin is required for non-image-forming photic responses in blind mice
Sleep & Circadian Health
- Phototransduction by retinal ganglion cells that set the circadian clock
- The mammalian circadian timing system: organization and coordination of central and peripheral clocks
- The two‐process model of sleep regulation: a reappraisal
- Melanopsin is required for non-image-forming photic responses in blind mice
- Strange vision: ganglion cells as circadian photoreceptors