Man has always tried to become independent from the Sun, searching for new sources of light to extend their activity time. The goal has been achieved, and the modern world functions 24 hours a day, 7 days a week. This is, among other things, the effect of the industrial revolution in the 19th century, and especially the discovery of the incandescent lamp by Thomas A. Edison in 1879.
Many other light sources have appeared since then, and the Edison bulb, which emitted large amounts of heat energy, is now mainly replaced by LED lighting (light-emitting diode), based on semiconductor light-emitting diodes. Relatively recently invented energy-saving LEDs emit different colours of light. They are characterised by a long life and versatile applications. Japanese scientists Isamu Akasaki and Hiroshi Amano and Shuji Nakamura from the USA received the Nobel Prize in Physics for the discovery of the blue LED in 2014.
Adverse effects of artificial light at night
Dynamic urbanisation and the widespread use of artificial light sources inside and outside rooms have resulted in the phenomenon of the so-called light pollution in the 21st century. More and more research indicates that excessive artificial light at night (ALAN), which disrupts the natural darkness of the sky, can have negative consequences for various ecosystems and for humans. It is already known that exposure to artificial light, especially at the wrong time, i.e. at night, leads to disruption of the circadian rhythm and, as a result, to sleep disorders, mood disorders, type 2 diabetes, obesity, cancer, etc.
What is the biological clock?
The human body, like that of most living organisms, functions rhythmically. It has an internal clock, based on the cycle of sunrises and sunsets, closely related to the 24-hour rotation of the Earth around its axis. This biological clock, called the circadian rhythm, is organised in an extremely complex way. It works in every tissue, in every cell of the body and is directed by the master clock located in a part of the brain called the hypothalamus. It has recently been proven that the circadian rhythm also has a genetic basis. The discovery of the operation of so-called clock genes in rodents by Americans Jeffrey C. Hall, Michael Rosbash and Michael W. Young was awarded the 2017 Nobel Prize in Medicine and Physiology.
Blue light
The alternating phases of activity and sleep in humans are a consequence of the synchronisation of the human body with the times of sunlight emission. It is indicated that the mechanism of the negative effect of ALAN concerns the inhibition of melatonin synthesis and leads to the disruption of the clock genes.
HEV (high-energy visible light) blue light, emitted by external and internal LED lighting and televisions, smartphones, tablets, laptops and computers, is considered particularly harmful to humans. On the other hand, you should not be afraid of white or blue lighting emitted by LEDs if you use it during the day, because then it helps you work, study, concentrate well and achieve a positive mood. The problem raised by doctors and scientists is the aforementioned ALAN, i.e. exposure to artificial light at night.
At the same time, light of a specific intensity (measured in lux) and wavelength is commonly used in phototherapy, e.g. in the treatment of seasonal depression, skin diseases or in cases of jaundice in newborn babies
Too little and too much sun
The beneficial effects of natural light mean that humans, as “children of the sun”, should have frequent contact with it. Insufficient exposure to UVB radiation in sunlight causes vitamin D3 deficiency and related to it negative health consequences. They are commonly observed in residents living at higher latitudes (including Poland). Insufficient dose of sunlight can lead to the development of seasonal depression in months when there is short exposure to the sun. On the other hand, doctors and scientists warn that excess solar radiation in the summer, especially on days with a high UV radiation index and staying in the sun between 11:00 a.m. and 3:00 p.m., can lead to the development of skin cancers.
Scientific research on the biological clock
Regardless of age, chronotype, i.e. preference for early or late activity during the day, occupation (e.g. shift work, 24/7 continuous work, office work, remote work), modern people should pay attention to healthy contact with light. This is because we are witnessing a global exposure to light, the long-term consequences of which we are still not able to predict. Scientists in a very broad range of fields dealing with light exposure, clock genes, melatonin, chronobiology, chronomedicine, etc. ae trying to do it. Research aimed at finding the clinical application of the biological clock in the treatment of civilisation diseases is of key importance here. For we know that the circadian rhythm in response to external stimuli, mainly light, coordinates many physiological, cellular and biochemical processes.
Prof. Edyta Reszka
Faculty of Biology and Environmental Protection, University of Lodz
edyta.reszka@biol.uni.lodz.pl
Prof. Edyta Reszka has been conducting research aimed at using one of the clock genes as a therapeutic target in the treatment of bladder cancer. Studies on pharmacological modulation of clock genes may constitute a new and promising anti-cancer strategy. Her research is financed by the National Science Centre under the OPUS 2020/37/B/NZ5/01684 project.
Edit: Press Office, University of Lodz