CSFrom 20 to 22 June 2024, the international chronobiology conference SLTBR 35th Annual Meeting – Society for Light Treatment and Biological Rhythms took place in Prague for the first time, bringing together more than 100 experts from all over the world in the field of chronobiology and circadian rhythms to present the results of their current research.
The regular alternation of light and dark has been an extremely reliable major variable in our environment for millions of years. Today, however, we spend more than 90% of our time indoors, where we are exposed to electric light of much lower intensity and often of a spectral composition quite different from that of natural daylight. In the evenings and before going to bed, we often still work in the light or spend time on our mobile phones or in front of a screen. The change in our behaviour due to modern technology has contributed, according to current research, to an increased incidence of diseases of civilisation such as metabolic syndrome, cardiovascular or neurological diseases, increased prevalence of prostate and breast cancer, as well as impaired cognitive function, performance and poor mental health (depression, anxiety, burnout).
Light and obesity
The speakers presented results that confirmed the above mentioned connections. Professor M. Zeman presented the findings that even exposure to 2 lx of light at night causes in male rats a disruption of circadian control of the hormonal system and loss of rhythmicity of the clock genes Per1 and Per2; disrupted rhythmicity of clock genes was also observed in other parts of the brain that transmit signals from the central clock (suprachiasmatic nuclei, SCN) to hormonal and behavioural rhythms. R. Taniguchi, in turn, confirmed the link between obesity in persons with bipolar personality disorder and exposure to light at night. The risk of obesity was much higher in persons who were exposed to light with illuminance >3 lx; these persons also had significantly higher weight.
The link between daylight and diabetes
Dr. J.-F. Harmsen presented the effect of daylight during working hours on people with type 2 diabetes. He found that exposure to daylight caused glucose levels to optimize to normal for a longer period of time compared to subjects in a control group who were exposed to lighting with a spectral course of a standard 300 lx LED bulb. Among other things, a metabolic shift in favour of fat burning is predicted from the results. Natural daylight illumination or, hypothetically, illumination similar to the spectral waveform of the sun with sufficient intensity could support the treatment and prevention of metabolic disorders such as type 2 diabetes. Glucose levels and circadian rhythm were also addressed by Dr L. Kervezee, who compared differences in nutritional support given continuously or only during the day in intensive care unit patients, as the interaction between circadian rhythm and metabolism is bidirectional.
Can light affect prostate disease?
Dr. G. Brainard presented results from his two in vitro studies in which he investigated the association between the progression of prostate cancer metabolism and low levels of melatonin in the blood. The results suggest that light that suppresses melatonin (daylight, blue monochromatic light, and fluorescent light as opposed to red light) may stimulate prostate cancer growth and metabolism in humans.
The effect of phototherapy on health and psyche
A large part of the lectures focused on bright light therapy (BLT) as an effective chronotherapeutic intervention in the treatment of mental and neurological diseases. Dr. D. Wescott presented on improving sleep quality and prolonging sleep and reducing depressive states in adolescents with depression using BLT after waking. Dr. R. Cox looked at the effects of light therapy in individuals with obsessive compulsive disorder (OCD) and noted improvement in symptoms after a 3-week treatment. Dr. P. Cheng presented the results of personalized light therapy for night shift workers. Dr. L. Maier and Dr. J. Kopřivová compared spectral differences of phototherapy devices using melanopic variables such as mEDI and mDER, which are far more important in terms of current science in relation to non-image forming (NIF) effects of light on the physiology and behavior of the organism. Current recommendations and methodologies in light therapy do not take into account the effect of the spectral composition of the light source, which are quite crucial in terms of outcomes.
The same was confirmed by Professor M. Spitschan, who presented a checklist for measuring, characterizing and describing light sources used in studies and clinical trials, in which 73% of the 60 scientists surveyed agreed that the spectral waveform of a light source is absolutely critical in characterizing light because it allows the calculation of many other metrics and is thus the easiest way to compare and support that studies have reproducible results. Indeed, it is important to remember that light does not only have visual effects but also NIF effects mediated by intrinsically sensitive retinal ganglion cells (ipRGCs) that are sensitive to the azure spectral components of light, and therefore it is necessary to replace the existing photopic quantities with melanopic quantities such as mEDI and mDER.
Sleep hygiene
Most of us associate the darkness hormone melatonin with circadian rhythms, which also received considerable attention during the lectures. Dr. R. Lazar’s research has produced results supporting the words of Associate Professor Z. Benda, who said that increased illumination and ample daylight can reduce the negative effects of light in the early evening and at night. R. Lazar concluded that increased exposure to bright light the previous day (>1000 lx) can effectively reduce the effects of evening light, which can cause night waking, and increase melatonin levels in the following days. Adaptation of circadian sensitivity to light may take longer, so regular and long-term proper light and sleep hygiene is recommended to achieve the desired results.
Light is the most important zeitgeber for our circadian rhythm, but regular timing of exercise (Dr. A. Hughes) and timed eating (Dr. Satchin Panda) is another factor we can focus on, as circadian health goes hand in hand with our overall health.
Mgr. Tereza Ulrichová, Spectrasol
