One of my favorite sites in the Cave is the Rafinesque Hall, where sleep studies were originally conducted by Nathaniel Kleitman and Bruce Richardson of the University of Chicago in 1938. The hall is named after Constantine Samuel Rafinesque( 1783-1840), a charismatic polymath who taught botany and philosophy at Transylvania University in Lexington, Kentucky’ s oldest university, founded in the year 1780.
Rafinesque explored the Cave, spending long hours studying some of the vast flora and the fauna. There are 120 species according to recent data, and one of the unique inhabitants, the bat with the strikingly big ears( Corynorhinus rafinesquii), was later named after him. Following the historic sleep study at Mammoth Cave, Nathaniel Kleitman continued sleep research with great passion and was the co-discoverer of REM sleep, gaining the distinction of being honored as the“ Father of Sleep Research.”
Our understanding of the physiology and the molecular basis of circadian rhythms and the biological clocks has been propelled by phenomenal advances in biotechnology. There is even a journal dedicated to publishing scientific papers related to circadian rhythms. Scientists have realized that circadian oscillators are ubiquitous in the body and the suprachiasmatic nucleus( SCN) in the hypothalamus functions as the central pacemaker. Photoentrainment of the SCN is achieved through input from melanopsin-containing retinal ganglion cells via the retinohypothalamic tract( RHT). The SCN controls production of melatonin by the pineal gland based on the amount of light received: inhibits during day and facilitates during night. The SCN, the master clock, coordinates the myriads of peripheral clocks through a complex system of neural and hormonal signals. 2017 was a major milestone for chronobiology with the Nobel Prize for Physiology or Medicine awarded jointly to Jeffrey C. Hall, Michael Rosbash and Michael W. Young. They were able to figure out how the biological clock works and explain how plants, animals and humans adapt their biological rhythm to synchronize with planet earth’ s rotation. By studying fruit flies, they identified the“ period” and its partner“ timeless” genes and the related proteins“ PER” and“ TIM.” They explained the generation of autonomous oscillation by a transcription-translation feedback loop( TTFL).
Let us get back to the question of the health hazards of disrupting the circadian rhythm, which can occur with several situations including the time change, travel through multiple time zones, shift work and space travel, to name a few. Circadian clocks play important roles in regulation of sleep, feeding behavior, hormone release, body temperature and blood pressure. Short term disruption of circadian rhythm leads to drowsiness and difficulty with focus and concentration resulting in potential errors and accidents. 1 Jet lag can also cause impaired judgement and slower reaction times leading to critical errors. Shift work may cause more lasting misalignment between endogenous circadian rhythm and the environmental day-night cycle. This misalignment may cause not only sleep-wake disturbances and impaired cognitive function, but also significant dysfunction resulting in metabolic syndrome, Type 2 diabetes mellitus and heart disease. 2 The American Academy of Sleep Medicine( AASM) opines,“ Daylight saving time is less aligned with human circadian biology, which due to the impacts of the delayed natural light / dark cycle on human activity, could result in circadian misalignment, which has been associated in some studies with increased cardiovascular disease risk, metabolic syndrome and other health risks. It is therefore, the position of the AASM that these seasonal time changes should be abolished in favor of a fixed, national, year-round standard time.” 3
While the debate on daylight saving time goes on, let us see what can be done to mitigate the deleterious effects of circadian misalignment resulting from the“ Fall back / Spring forward” ritual every year. The daylight-saving transition can be made less jarring by advancing the sleep-wake schedule gradually over a week to align with the new time; one can advance the sleep onset and wake up times by 15 minutes every two to three days prior to the night of the time change. Exposure to morning sun is an effective way of fine tuning the circadian clock to align with the new sleep wake schedule. Exposure to bright light( 10,000 lux with high blue spectrum) for 30 minutes is an alternative. Short term use of melatonin in low doses, about 30-60 minutes before the desired bedtime, has also been found to be useful.
Olivia Judson, the evolutionary biologist and science writer, predicted this in 2009.“ Therapy by the clock( chronotherapy) will be the next major healthcare development, with treatments and meals timed to our internal clocks.” 4 Her prediction has been validated by the tremendous advances in every aspect of applied chronobiology, especially chronotherapy and chrono pharmacology.
References:
1
Woods A N, Weast RA, Monfort SS. Daylight saving time and fatal crashes: The impact of changing light conditions. J Safety Res. 2025 93:200-2o5.
2
Boivin D, Bourdreau P, Kosmadopoulose A. Disturbance of circadian system in shift work and its health impact. J Biol Rhythms. 2021:37( 1): 3-28
3
Rishi MA et al. Daylight-saving time: an American Academy of Sleep Medicine position statement. J Clin Sleep Med. 2020; 16( 10): 1781-1784
4
Judson, O. Enter the Chronotherapists. The New York Times Opinionator. https:// opinionator. blogs. nytimes. com / 2009 / 12 / 22 / enter-the-chronotherapists /
Dr. Iyer practices at the Neurodiagnostic Center of Louisville and is a retired professor of neurology at the University of Louisville School of Medicine.
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