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Red light lowered glucose spikes
The glucose test
Glen Jeffery's lab fasted the volunteers, gave them a glucose drink, and tracked how fast blood sugar rose. With red light shining on their backs, the peak fell by more than 25% and the rise slowed. It worked on bare skin and through a T-shirt.
How the light travels
Long-wavelength light travels deep. Red penetrates about eight centimeters into the body, and infrared passes all the way through. Along the way it changes how mitochondria handle electrons, so they work more efficiently. The sun gives off all of it, and the warmth felt from sunshine is that infrared.
Melatonin and LEDs
Melatonin also sits inside most cells of the body, where it acts as an antioxidant instead of a sleep signal, and long-wavelength light is what frees it up. Evidence from Jeffery's lab and others suggests indoor LED light, heavy on short wavelengths, may damage mitochondria.
Why does red light travel so deep?
Blood and water absorb blue and green light strongly, so those colors stop within a fraction of a millimeter of the surface. Wavelengths from roughly 650 to 900 nanometers are absorbed far less, and researchers call that stretch the optical window of tissue. Hemoglobin in particular lets red and near-infrared light pass. That is why a flashlight pressed against a fingertip glows red on the other side.
Why would mitochondria respond to light?
An enzyme at the end of the mitochondrial electron transport chain, cytochrome c oxidase, absorbs red and near-infrared light. Researchers in the field called photobiomodulation consider it the leading candidate for how the light has any effect. The enzyme hands electrons to oxygen as the last step in making ATP. Its light absorption was first characterized in the 1970s.
Why are LEDs heavy on short wavelengths?
Most white LEDs pair a blue LED chip with a yellow phosphor coating, which gives a sharp spike of light around 450 nanometers. Incandescent bulbs glow broadly across the spectrum and give off large amounts of red and infrared. Fluorescent tubes concentrate their output in a few narrow bands. Sunlight spans the whole range from ultraviolet through infrared.
How does melatonin work inside cells?
The pineal gland releases melatonin into the blood at night, and that circulating pulse is the sleep-timing signal. Melatonin is also a strong antioxidant that neutralizes reactive oxygen molecules. Researchers including Russel Reiter have reported that mitochondria can make their own melatonin. The amount in the blood is only a small fraction of what cells hold in total.
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