Rhythmicity is a part and parcel of the human life. We have daily rhythms (eat, sleep), monthly rhythms (menstrual cycle every 28 days generally) or even annual rhythms (annual migrations in prehistoric humans). These are generally driven by the earth’s daily rotation at 23.5 degrees, the seasons and the annual orbit around the sun. The circadian (circa – about and dia – a day) rhythms is the natural 24-hour cycle that governs our physiological, mental and behavioral aspects like sleepy ness and wakeful ness. It is governed by a small area of the brain above the optic chiasm. That’s why circadian rhythm is majorly influenced by light and dark as they signal from the eyes and sends out signals to the rest of the body so that all systems run on a uniform schedule. It can also be influenced by stress, behavior and environmental factors.
The study of body clocks goes back to the 1720s when a French scientist, De Mairan showed that the Mimosa Pudica or the sensitive plant which folded and unfolded its leaves in response to a 24-hour pattern even when kept in compete darkness. About 250 years later, Nathaniel Kleitman, one of the pioneers of sleep research, showed the same behavior in humans.
According to Prof. Putnam, Professor of Neurology and Neuroscience at Harvard Medical School, “Circadian rhythms penetrate every aspect of life”. It influences heart rate, blood pressure, body temperature, hormone levels and urine production. Its disruption has been linked to obesity, cancer and depression (Harvard Medical School, 2018).
An important yet unknown till recently was the fact that there is just not one clock in the human body. Yes, the “master clock” does reside in the brain in the hypothalamus region, but there are numerous such clocks in liver, pancreas, adipose tissue and muscles. Damage to the master clock does disorganize the synchronicity of all these cellular peripheral clocks but these clocks tick away nevertheless at their own rhythm (Albrecht, 2012).
What does it all mean for us? Well, at one level, it means that proper and regular sleep keeps our circadian rhythm uniform with its attendant advantages for physical and mental health. As a corollary, any changes to our sleep patterns, stress or other physical factors disorients the master clocks and gives rise among other things to sleep disorders. The main circadian rhythm related sleep disorders are
1. Jet Lag – this is the most common and happens when one travels across time zones and finds it difficult to adjust to the new sleep wake schedules. This could cause insomnia, daytime sleepiness, indigestion among other things. Sometimes its is advised to take melatonin to bring the body lock back to sync but according to Prof. Russell Foster, exposing oneself to the morning or afternoon light (depending whether we have travelled east or west) helps the body adjust faster (Foster, 2023)
2. Shift Work: Night shift workers have their circadian rhythms misaligned to the sleep wake cycles. The resulting sleep disorder has been linked to obesity, type 2 diabetes and even cancer (Costa, 2010).
3. Delayed sleep phase disorder (DSP): People with DSP generally sleep later and wake up later (Night owls). This is more common in adolescents and can interfere with school or work life and cause mental stress.
4. Advanced sleep phase disorder (ASP): While more common in older adults, this disorder can also interfere with daily plans and also might decrease the sleep duration due to earlier than usual wake times.
Circadian Rhythm Sleep Disorders happen due to a lot of reasons and sometimes it’s a part of growing up or growing old. But, if certain underlying conditions are suspected, professional help should be sought and certain therapies like bright light exposure in the evening can help push the sleep phase to later in ASP and sometimes melatonin supplement under the guidance of an expert can be sought.
References:
Albrecht U. Timing to perfection: the biology of central and peripheral circadian clocks. Neuron. 2012 Apr 26;74(2):246-60. doi: 10.1016/j.neuron.2012.04.006. PMID: 22542179.
Foster, R: (2023). Life Time. Penguin
Costa G. Shift work and health: current problems and preventive actions. Saf Health Work. 2010 Dec;1(2):112-23. doi: 10.5491/SHAW.2010.1.2.112. Epub 2010 Dec 30. PMID: 22953171; PMCID: PMC3430894.
Circadian Rhythms and the Brain (Harvard Medical School, 2018)