From 20 to 22 June 2024, an international chronobiology conference took place in Prague for the first time: SLTBR 35th Annual Meeting – Society for Light Treatment and Biological Rhythms, which brought more than 100 experts from around the world in the fields of chronobiology and circadian rhythms together to present the results of their latest research.
The regular alternation of light and dark has been an extraordinarily reliable major variable in our environment for millions of years. However, today we spend more than 90% of our time indoors, exposed to electric light of a much lower intensity and often a completely different spectral composition than 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. According to the latest research, the change in our behaviour due to modern technology has contributed to an increased incidence of civilisational diseases such as metabolic syndrome, cardiovascular and neurological diseases, increased prevalence of prostate and breast cancer, as well as impaired cognitive function, performance and mental health (depression, anxiety, burnout).
Light and obesity
The speakers presented results that confirmed the aforementioned correlations. Professor M. Zeman presented findings that exposure to as little as 2 lx of light at night causes disruption of circadian control of the hormonal system and loss of rhythmicity of the Per1 and Per2 clock genes in male rats, and that disrupted rhythmicity of clock genes has also been observed in other parts of the brain that transmit signals from the central clock (suprachiasmatic nuclei, SCN) to hormonal and behavioural rhythms. R. Taniguchi confirmed the link between obesity in people with bipolar personality disorder and exposure to light at night. The risk of obesity was much higher in people who were exposed to a light of illumination >3 lx; in addition, these people had a significantly higher weight.
The link between daylight and diabetes
Dr J.-F. Harmsen presented the effects of daylight during working hours on people with type 2 diabetes. He found that exposure to daylight caused glucose levels to optimise to normal for prolonged periods of time compared to subjects in the control group who were exposed to lighting with a spectral course of a standard 300 lx LED bulb. Among other things, the results suggest a shift in metabolism in favour of fat burning. Natural daylighting or, hypothetically, lighting similar to the spectral pattern of the sun with sufficient intensity could support the treatment and prevention of metabolic disorders such as type 2 diabetes. Glucose levels and circadian rhythms were also studied by Dr L. Kervezee, who compared differences in nutritional support administered on an ongoing basis or only during the day in intensive care unit patients since the interaction between circadian rhythm and metabolism is bidirectional.
Can light affect prostate diseases?
Dr G. Brainard presented the results of his two in vitro studies, within which he investigated the links 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 tumour growth and metabolism in humans.
The effect of phototherapy on health and psyche
A large portion of the lectures focused on bright light therapy(BLT) as an effective chronotherapeutic procedure in the treatment of mental and neurological diseases. D. Wescott, a Ph.D. candidate, threw a presentation on improved sleep quality, prolonged sleep and reduced depressive states in adolescents with depression thanks to using BLT after waking. Dr R. Cox studied the effects of light therapy on people with the obsessive-compulsive disorder (OCD) and saw improvement in symptoms after three weeks of therapy. Dr P. Cheng presented the results of personalised light therapy for night shift workers. Dr L. Maier and Dr J. Kopřivová compared the spectral differences of phototherapeutic devices using melanopic variables such as mEDI and mDER, which, from the point of view of the state-of-the-art, are much more important in relation to the non-imageforming (NIF) effects of light on the physiology and behaviour of the organism. Current advice and methodologies in light therapy fail to take into account the influence of the spectral composition of the light source, which is crucial for the results.
The same was confirmed by Professor M. Spitschan, who presented a checklist for measuring, characterising 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 essential in characterising light, as it allows the calculation of many other metrics and is, therefore, the easiest way to make comparisons and support the reproducibility of results of studies. It should be noted that light not only has visual effects but also NIF effects mediated by the intrinsically photosensitive retinal ganglion cells (ipRGCs), which are sensitive to the cyan spectral components of light, thus bringing about the need to replace the existing photopic variables with melanopic variables such as mEDI and mDER.
Sleep hygiene
Most of us associate the darkness hormone melatonin with the circadian rhythm; this was also given considerable attention during the lectures. Dr R. Lazar’s research produced results supporting the words of Associate Professor Z. Bendová, who said 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 can take longer, so regular and prolonged proper light and sleep hygiene is recommended to achieve the desired results.
Light is the most important timer for our circadian rhythm, but regular timing of exercise (Dr A. Hughes) and timed eating (Dr Satchin Panda) are other factors we can focus on as circadian health goes hand in hand with our overall health.
Mgr. Tereza Ulrichová, Spectrasol
