Sunlight is known to increase the production of Vitamin D in the skin via frequencies in the ultraviolet (UV) spectrum. Some believe that the near-infrared (NIR) and infrared (IR) spectrums can increase melatonin production in mitochondria. Is this true?
The answer to this question is: it depends. Let me explain why.
We now know that the melatonin found circulating in the blood is produced only at night by the pineal gland. Any amount of light will suppress pineal production, day or night [1,2]; even intense red light at night can suppress melatonin production in animals [3,4]. However, more than 95% of melatonin in the human body is produced in mitochondria [5]. This production is not affected by the light/dark cycle, and is active 24/7.
So this raises a very interesting question: how does the NIR/IR spectrum increase melatonin in mitochondria, if at all?
In a well-written hypothetical review, Zimmerman and Reiter discussed the potential of increasing melatonin using NIR/IR frequencies. They proposed that the NIR portion of natural sunlight stimulates an excess of antioxidants including melatonin in order to enhance the body’s ability to rapidly and locally deal with changing conditions throughout the day [6]. The discussions did not include the mechanism by which NIR increases mitochondrial production, but several examples in literature were used to support their hypothesis. Lamentably, the primary example was a study that showed an increase in circulatory melatonin (produced by pineal glands) in female athletes using whole body exposure to 670 nm NIR at night and not sunlight during the daytime [7].
This means that there is currently no evidence from literature that shows that NIR/IR spectrum from sunlight exposure can conclusively increase melatonin production during the daytime in mitochondria.
Interestingly, there is evidence showing that blue light exposure during the daytime increases NIGHT TIME melatonin levels in animal models [8]. Rats kept in different colored cages have the same daytime levels of melatonin, but rats kept in blue cages have higher plasma melatonin at night compared to those kept in amber and clear cages [8].
