Melatonin is fundamental to the lighting, display, and architectural industries as the primary biomarker used in circadian theory. Billions of dollars are being spent on research, product development, and marketing based on the impact of visible light on melatonin produced by the pineal gland. It has now been shown that the mitochondria produce melatonin in many cells in quantities which are orders of magnitude higher than that produced in the pineal gland. This subcellular melatonin does not necessarily fluctuate with our circadian clock or release into the circulation system, but instead has been proposed to be consumed locally in response to the free radical density within each cell, in particular in response to Near Infrared (NIR) exposure. The main point of this review hypothesizes that the subcellular melatonin is being produced in response to the NIR photons which make up the majority of natural sunlight. Given the number of cells and quantity of subcellular melatonin identified to date, it is reasonable to propose that the body produces and maintains a melatonin reservoir that is separate and apart from the circulatory melatonin generated by the pineal gland. To understand how sunlight may support or stimulate this antioxidant reservoir, it becomes necessary to quantify the free radical density in various parts of the human body. To do this, it is necessary to move away from two-dimensional empirical approaches and develop three-dimensional bio-optical models based on the underlying biological processes at play. Three-dimensional Mechanistic Bio-optical Models (MBM) of the skin, eye, and brain based on non-sequential optical ray tracing and Electron Spin Resonance (ESR) data clearly indicate that the NIR portion of natural sunlight provides the primary stimulus during the day to the majority of the cells in the human body, impacting over 60% of the cells in an adult body and 100% of the cells in the fetus and young children. It is also shown that optically, the human body, under the assumption of natural sunlight, has developed optical mechanisms to gather and localize NIR photons in the most sensitive areas of the human body: blood vessels, retina, brain, skin, and even the fetus. That assumption is no longer valid in modern societies where the majority of our time is spent exposed to visible only lighting and displays, which emit zero NIR photons. Based on an optical and biological review of the literature and the MBM results, it is proposed that the NIR portion of natural sunlight stimulates an excess of antioxidants in each of our healthy cells and that the cumulative effect of this antioxidant reservoir is to enhance the body’s ability to rapidly and locally deal with changing conditions throughout the day. In this approach the role of circulatory melatonin produced by the pineal gland is to provide an efficient method of delivering supplemental melatonin during periods of low cellular activity and solar stimulus to damaged or aging cells in both diurnal and nocturnal animals. While circulatory melatonin may be the “Hormone of Darkness”, subcellular melatonin may be the “Hormone of Daylight”.
The Integrative Five-Fluid Circulation System in the Human Body