Circadian rhythms and their relevance to mental wellbeing
Circadian rhythms and their relevance to mental wellbeing
Some of us seem to suffer the blues each winter. This, it turns out, is a real, not an imagined phenomenon. The article below describes the physiological and mental states that are brought on by the light-dark cycle of daily life, seasons and climate.
Circadian rhythms (CR) are the daily rhythms influenced by light and darkness that help us to wake up or go to sleep. They make up, generally speaking, a 24-hour cycle which alters with daylight, seasonal-light and climate. The dimness of the winter light is said to affect our CR. Other conditions also affect CR – these include night shift work, jet lag, diet, poor sight, life in submarines, spaceflight, polar winters where there may be at certain times of the year an absence of any environmental light-dark cycles, and blindness. Human beings and other organisms are affected by changes in the amount of light in their lives to the extent that they may have trouble sleeping and suffer significant emotional and physical disruption. Depressive states are exacerbated by the reduction or total lack of a light source (Jones, 2015; Foster, 2015; Skene 2015).
Writing from an evolutionary point of view, when early humans evolved to live out of trees, on land and in groups, it was useful for them to be able to predict daylight to gather food and dark so they could rest. CR accords with this and our brains have adapted to these cycles. Light affects neural connections and alertness. Serotonin and anti-depressant drugs do the same thing, except they produce side effects too. CR aids the production of melatonin and cortisol, hormones secreted from the hypothalamus in the brain. During the daylight hours, cortisol is produced and when it starts to get dark, melatonin is produced.
Melatonin, which is involved in regulating sleep rhythms, is suppressed by exposure to light and cortisol regulates alertness. All of these reactions occur through the perceiving of light through the retinal cells in the eyes (Lockley et al., 2007).
Caves provide very dark environments. When researchers stayed in caves for a period of six months, they found that their CR drifted away. In another experiment, prisoners were kept in bright light with a similar result – disrupted CR and sleep disorders. Dr Steve Jones of University College, London states that light is the big factor, adding that because CR can be flexible, it can actually be set by switching on a light. (BBC Radio 4 In Our Time)
Circadian rhythms are often referred to as the body clock. This ‘body clock’ can also affect athletic performance. Evidence from studies carried out over 25 years of Monday Night Football in the USA have shown that alertness, reaction times and certain types of physical strength are all influenced by the body clock (Reilly & Percy, 1994). Football matches on the east coast of the USA often start at 21:00 local time and last for two hours. At the end of the two hours (23:00 local time) the players would start to become less alert. When they were playing teams from the west, where there was a time lag of three hours, east coast players were unfairly disadvantaged. Conversely, western teams were at their peak alertness and this was reflected in the scores, with the western teams winning more often and by larger margins (Korb, 2015).
How CR works
It is well established that light is the stimulus for the body clock – there is an interaction between light and the internal world of the body. The medium in human beings and other mammals is vision: light enters the body through the rods and cones, light sensitive cells in the retina. At the bottom of the retina is a layer of ganglion cells one percent of which are sensitive enough to transmit light energy signals from the eye to the optic nerve and further on to the hypothalamus in the brain. The hypothalamus comprises about 50,000 supra-charismatic nuclei (SCN), cells sensitive to light and dark. In mammals, SCN generate 24-hour oscillations. This means that one neurone (nerve fibre) will oscillate every 24 hours in accord with the light-cortisol or the dark-melatonin pattern. CR is, therefore, a “sub-cellular molecular-feedback loop”. (BBC Radio 4 In Our Time)
Previous work on genes and their behaviour has shown that CR are endogenous (generated within); between twelve and fourteen key genes in each body cell are affected by CR, so when it is light the organism wakes up and when it is dark it feels sleepy. Thus, to help them regulate patients’ sleep and waking times with drug use, it is useful for general practitioners (GPs) to know their patients’ light-dark rhythms. Even the blind regulate their body clocks but there are differences in human beings depending on their location; those who live closer to the equator, where there are 12-hour days, expect darkness at a regular time each day whereas in Europe, CR clocks are more labile and change with the conditions of light and dark.
Giving birth for many mammals can be a time of great vulnerability from predators. Many mammals give birth at night, often the most inactive time for the new mother and her group, who may be constantly on the move during the day. Nevertheless, some monkeys and apes give birth around the clock.
For women, there is a peak at around midnight and a trough at midday. Research carried out in Switzerland between 1926-1930 demonstrated that of more than 350,000 births, the highest number of births occurred between 02:00 and 05:00 and the lowest number between 13:00 and 19:00; when the onset of labour was taken into consideration, there was a clear peak at 02:00. This statistic was confirmed by Dr Alison Jolly (1972) but was later questioned by Dr Robert Martin who maintained that it is also vital to know “…whether birth hour is related to frequency of premature birth, incidence of postnatal depression or difficulties in initiating breastfeeding—all of which have been climbing for unknown reasons” (Martin, 2015).
Teenagers, owls and larks
Research has shown that changes to circadian rhythms occur during adolescence, when most teenagers experience a sleep phase delay; melatonin levels in teenagers’ blood rise naturally later at night than in most children and adults.
This could be an explanation for the discord in teenagers starting school as early as 08.30, when their cortisol secretions have not caught up with school timetabling, and for the fact that they are able to stay awake long past their parents’ natural bedtimes.
We all have friends who claim to be larks (morning people) or owls (night types). There is more to this idea than meets the eye. The cycle length of the endogenous period varies between 23.8 and 24.8 hours, a periodicity that occurs when proteins enter the SCN cells, turn off the clock and create morning and evening people. People also experience dips and rises in their circadian rhythms at different times of the day. For example, in adults, the strongest need to sleep generally occurs between 02:00-04:00 and between 13:00-15:00, when many who live in southern Europe take siestas.
Blind and Visually-impaired people
In a study of sighted humans who were instructed to avoid having large meals, to remain still and not to carry any timepieces with them, measurements of hormones, temperatures and performance were carried out in relation to changes in their CR. This was compared to a study with people who had visual impairments and others who could see no light at all. The results showed that in people who can see some light, CR remained in synchronisation with the daily light-dark cycle, but in totally blind people, CR were missing even though the body clock was present. The researchers also found that use of melatonin helped blind people sleep at night and experience less drowsiness during the day; with no light cues at all, the body clock will remain desynchronised and can only be turned on and off artificially.
Desynchronisation of CR
Desynchronisation is like jet lag – depending on how far away you are from your normal awake-sleep cycle, daytime can feel like the middle of the night and vice versa. Napping during these periods does not help to regulate circadian rhythms which are also affected by food, exercise and caffeine. Animals have very similar clock genes; rats tend to sleep in the middle of the day but if they are fed at that time, they start to desynchronise and change their patterns of sleep and feeding (BBC Radio 4 In Our Time).
Shift work can be a major difficulty for people who work shifts; while one or two nights do not desynchronise CR, it is questionable whether or not longer shifts – for example, three-week shifts – are healthy. Skene (2015) reports that there could be a connection between cancer or metabolic syndrome (obesity, raised blood pressure and high cholesterol) and shift work and Foster (2015) explains that shift workers don’t adapt well to bright light at night suggesting that this can alter the CR (BBC Radio 4 In Our Time) . “Other functions also become desynchronized under such conditions, for example, postprandial (after meals) metabolism. When meals are taken during the biological night, they cannot be metabolized as efficiently as when eaten during the day, and consequently postprandial levels of glucose, insulin, and fats are elevated. In the long term, the regular impairment of metabolism induced over years of shift work may lead to chronically elevated circulating levels of insulin and fat, and may increase the risk of developing insulin resistance, diabetes, or cardiovascular disease. Gastrointestinal discomfort is also a common complaint” (Lockley et al., 2007).
It has been shown that shift work results in changes to sleep patterns and disrupts normal circadian rhythms, leading to “low mood or full major depression” (Cline, 2012) and a study of 200 NASA employees revealed lower than normal morning cortisol levels affected their CR (Caplan et al, 1979). It has also been shown that a change from a day-shift to a night-shift, or a 12-hour shift in time zone, is too rapid for the internal clock to bring about an effective adaptation; in some cases, adaptation to a new time zone or night shift can take up to two weeks during which time the quality of sleep is impaired. For people working during the night, daytime sleep can often not be long enough, resulting in impaired performance and possibly accounting for the higher incidence of work place injuries for shift workers.
It is worrying to read that, in the UK, people today leave the house one hour earlier than they did twenty years ago. Many spend their work and leisure time in front of blue-light emitting machines and it has been suggested (Jones, 2015) that this affects the CR clock and can cause depression. It is common for teenagers and others to sit in front of a screen long into the night at a time when it is dark and they should be sleeping. When humans sleep, they also dream. During this time, rapid eye movement (REM) occurs, perhaps only for minutes, but in this short time the memory is organised in the brain. Not only can a lack of sleep cause depression, but interruption of this useful sleep period can be detrimental to the functions of the memory. Moreover, from what we know already about sleep deprivation, it is widely accepted that torture practices, whereby sleep is withheld or constantly interrupted, lead to disorientation and confusion.
During the winter months when the sun is low in the sky and, in some countries, the sky is constantly grey, a potentially serious condition – Seasonal Affective Disorder (SAD) – can emerge and result in mood changes and depression. Kryver (2013) states that SAD can be so serious that some people can be led to suicidal ideation. These depressive episodes are due to the reduction of cortisol, which wakes us up and is associated with brighter light levels. Although the evidence is not conclusive, there are trials using light therapy to treat SAD and during debates about visual damage or blindness in human beings, Kryver has reported positive results to light therapy when light has been aimed at the ear canal. (ibid)
Treatment for desynchronised CR
Half a gramme of melatonin at the same time each night is recommended lifelong administration once the CR pattern has become irregular. There is a warning that should treatment cease, the irregularity will recur (Lockley et al, 2007; Jones, 2015). In the UK, melatonin does not have a safety and efficacy certificate and therefore cannot be bought in pharmacies, but it can be prescribed.
Artificially bright light will reduce jet lag and help to control the body clock for shift workers; bright light therapy has been suggested as a remedy for SAD. Interpersonal social rhythm therapy (learning to manage sleep and wake times, meal times, interpersonal relationships and the timing of social contact) has also been recommended to aid desynchronised CR and agomelatine (an antidepressant), can be used as a target for melatonergic receptors (receptors for melatonin) (Boyce et al, 2010).
Relevance to psychotherapy
The relevance and importance of circadian rhythms to psychotherapists is in knowing about the effects of sleep deprivation, sleep disorders and unhealthy sleeping patterns. While many clients may need some extra help from their GPs, sometimes antidepressants can be disruptive to sleep, further exacerbating depressive states and moods. Knowledge about circadian rhythms and sleep disorders can pinpoint some questions for clients, questions which can then be relayed to their GPs. For example, if sleep disruption is one cause of depression, can the GP address this? And if their medications are disrupting their daily rhythms, will the GP be able to look at alternatives or different dosages? And, in the event of the discovery that the hormones melatonin and cortisol are out of balance, could the GP offer some kind of solution to this? Acknowledgement of ‘winter blues’ (SAD) may also help the patient feel more normal.
But there are also cultural issues that are questionable, especially in the UK where the binge culture seems to have taken hold. Staying up drinking all night is not only a threat to physical health, it also disrupts CR; one night awake results in sleeping all day to recover, not only from the night without sleep but also from the hangover. Could this cultural phenomenon bring about a generation of serotonin-deprived beings later in life? Will a whole generation need compensation through antidepressants? And what of the Internet revolution? Will that result in a generation of people who cannot sleep, whose CR is regularly disrupted and desynchronised? Will the consequences of this mean that generations of working people will become dependent upon artificial aids to function? Only time will tell.