Assignment: Circadian Rhythms

Assignment: Circadian Rhythms

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Assignment: Circadian Rhythms

Most of us at one time or another have experienced a change in schedule that has contributed to both sleep deprivation and an upsetting of our circadian rhythms. In this discussion we will explore the effects of such changes. After watching the video Rhythm and Snooze – Circadian Genes located at http://www.youtube.com/v/17L5S7Kk7Cc?version=3, respond to the following:

1. How were you affected the last time you experienced multiple instances of having to get up unusually early, stay up much later than you are accustomed to or experienced some other change in sleeping patterns?

2.  Are you an “owl” or a “lark”?  Have you always been owl-ish or lark-ish or were you different in prior periods of your life?

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3.  How well does your owl-ness or lark-ness match the wake/sleep schedule you are currently experiencing, which can vary widely between individuals and be governed by a number of daily life demands, from non-optional work shifts, to being a new parent with an infant not concerned with your desire to sleep through the night, to your choice of leisure activities?  What do this week’s readings tell you about the potential positive or negative impacts of your particular matching or non-matching wake/sleep schedule?  How well do the impacts, for better or worse, suggested in the readings align with your actual experience (e.g. if you are a lark whose schedule requires you to work a late evening shift or an owl who has to rise very early to get children to school, do you find yourself running low on energy during times of the day or night when you normally don’t or having trouble concentrating)? Assignment: Circadian Rhythms

The most important rhythms are circadian and menstrual.
Circadian changes mean changes over the 24 hours of the day-night cycle and is best shown for the glucocorticoid cortisol axis. plasma cortisol levels measured over 24 hours-levels are highest in the early morning and lowest overnight. Additionally, cortisol release is pulsatile, following the pulsatility of pituitary ACTH. Thus ‘normal’ cortisol levels (stippled areas) vary during the day and great variations can be seen in samples take only 30 min apart. The circadian (lightdark) rhythm is seen in reverse with the pineal hormone, melatonin, which shows high levels during dark, though there is no clear clinical role for this.
The menstrual cycle is the best example of a longer (28-day) biological rhythm.

The Importance Of Circadian Rhythms In Shift Work Biology Essay

Our lives are structured around 3 different clocks; the social clock, the solar clock (light/dark cycle) and the endogenous biological clock (Roenneberg et al., 2003). The biological clock controls physiological functions at numerous levels from gene expression and body temperature to regulating mental and physical processes. These rhythms are generated over a period of between 24 and 25 hours (Klerman et al., 2001, Reilly et al., 2009). Chronobiology is the study of biological rhythms in living organisms. Exogenous rhythms e.g. the light/dark cycle play a vital part producing external environmental cues called zeitgebers. Circadian rhythms are not dependent on zeitgebers but can adjust and synchronise to them. This is called entrainment. (Borisenkov et al., 2011, Forbes-Robertson et al., 2012, Roenneberg et al., 2007, Waterhouse et al., 2002). Assignment: Circadian Rhythms

Research in this area is relatively new and much has been focussed on the basic biology in animals and humans. There is relatively little that addresses how this impacts significant human behaviour and performance. There are some difficulties in doing this research because of the inter-connectedness of so many factors – especially current lifestyle/environmental factors (including social, dietary, seasonal etc.) interacting with basic biological pre-dispositions.

Some research into circadian rhythms suggests that, not only is it highly important but also that it is highly individual. This means that individuals have different rhythms depending on their circadian preference and will need to address their shifts and preparation differently. However, understanding these individual differences have, so far, been much neglected. A thorough analysis and history of each individual is essential for the evaluation of any sleep problems, performance maxima and minima and feeding patterns. Individual clocks entrain to environmental cues differently and this is called a person’s chronotype (early, intermediate or late) (Allebrandt & Roenneberg, 2008). Establishing an individual’s chronotype is crucial to understand specific effects and nature of rhythmicity in an individual. Differences between chronotype can be displayed by different sleep/wake cycles, timing of cortisol and melatonin release, core body temperature patterns and autonomic nerve reactions (Urbán et al., 2011).

The few studies that did identify the chronotype of individuals failed to include all 3 chronotypes (early, intermediate and late) and used small sample sizes causing a generalisation of optimal performance times. Most studies concluded that afternoon/late evening was the best time to achieve peak performance, which is not a true representative of the results as it may just be the case for the population tests (Intermediate types). Roenneberg et al., (2003) suggested that the peak performance time for Intermediate/Late types is in the late afternoon or early evening because they are suffering from sleep inertia (impaired alertness) for most of the morning during the working week when required to follow an early schedule. There is about a 4hr discrepancy between time of high activity in early and late types (shown in figure 1).

Figure1: A diagram to show that there is about a 4hr discrepancy between the onset of high activity in late and early types. It may therefore be suggested that their peak mental performance should take place in this time slot when they are most physically and mentally alert.

There are several factors that make the examination of rhythms problematic.

GENDER: Exploring the differences between female and male peak performance times may also be interesting as research into this appears to be lacking. Roenneberg, (2003) showed that using self-report questionnaires females advocate themselves as slightly earlier in circadian preference than men. Consequently there may be a difference in peak performance times.

LIFESTYLE AND SLEEP PATTERNS: Sleep has 2 important properties; timing and duration (Allebrandt et al., 2010). These factors don’t just depend on individual circadian preferences but environmental external factors and time spent awake. The literature suggests that less regular schedules i.e. shift work and life styles cause various problems with sleep/performance due to desynchronisation of external environmental factors and endogenous body clocks. Sleep deprivation studies have been used to demonstrate that fragmented sleep or lack of sleep can have a huge effect on cognition and mental performance (Benoit et al., 1996).

GENETICS: Mammalian molecular clock mechanisms are controlled by clock genes. Changes in these genes due to polymorphisms or mutations may be linked to differences in circadian preference. The literature suggests that clock genes can be associated with problems linked to sleep quality, dysfunctional rhythms and changes in mood (Allebrandt et al., 2010). Osland et al., 2011 proposed that genetic components contribute to differences in circadian preference by investigating variable number tandem repeat (VNTR) polymorphisms in the human period3 (per3) gene. Different groupings of alleles associated with per3 were reported to be linked with particular circadian preferences. Individuals that are homozygous for the 5 repeat allele Per3 (5/5) have been linked to show early type circadian preferences. The reason for this could be because this particular VNTR polymorphism causes a ‘phase advance’ in circadian rhythmicity by increasing slow wave activity (SWA) in non-rapid eye movement (REM) sleep and increasing theta/alpha activity during the day. This causes an increase in the susceptibility to sleep loss and also a higher deterioration of cognition when sleep deprived. The 4 repeat allele Per3 (4/4) has been connected with late type circadian preferences; initiating a ‘phase delay’. Finally per3 (4/5) is linked to intermediate type circadian preference (Dijk et al, 2010). More investigations are needed to substantiate the genetic elements involved in circadian preferences (chronotypes).

If this area was more researched and understood it could provide people with the information they need to minimise sleep deprivation, optimise shift work schedules, and maximise peak performance.

References –

ALLEBRANDT, K. V. & ROENNEBERG, T. 2008. The search for circadian clock components in humans: new perspectives for association studies. Braz J Med Biol Res, 41, 716-21.

ALLEBRANDT, K. V., TEDER-LAVING, M., AKYOL, M., PICHLER, I., MÜLLER-MYHSOK, B., PRAMSTALLER, P., MERROW, M., MEITINGER, T., METSPALU, A. & ROENNEBERG, T. 2010. CLOCK gene variants associate with sleep duration in two independent populations. Biol Psychiatry, 67, 1040-7.

BENOIT, O. 1996. [Sleep-wakefulness rhythm disorders]. Rev Prat, 46, 2442-7.

BORISENKOV, M. F. 2011. The pattern of entrainment of the human sleep-wake rhythm by the natural photoperiod in the north. Chronobiol Int, 28, 921-9.

DIJK, D. J. & ARCHER, S. N. 2010a. PERIOD3, circadian phenotypes, and sleep homeostasis. Sleep Med Rev, 14, 151-60.

FORBES-ROBERTSON, S., DUDLEY, E., VADGAMA, P., COOK, C., DRAWER, S. & KILDUFF, L. 2012. Circadian disruption and remedial interventions: effects and interventions for jet lag for athletic peak performance. Sports Med, 42, 185-208.

KLERMAN, E. B., ZEITZER, J. M., DUFFY, J. F., KHALSA, S. B. & CZEISLER, C. A. 2001. Absence of an increase in the duration of the circadian melatonin secretory episode in totally blind human subjects. J Clin Endocrinol Metab, 86, 3166-70.

OSLAND, T. M., BJORVATN, B. R., STEEN, V. M. & PALLESEN, S. 2011. Association study of a variable-number tandem repeat polymorphism in the clock gene PERIOD3 and chronotype in Norwegian university students. Chronobiol Int, 28, 764-70.

REILLY, T. & WATERHOUSE, J. 2009. Sports performance: is there evidence that the body clock plays a role? Eur J Appl Physiol, 106, 321-32.

ROENNEBERG, T. 2003. The day within. Chronobiol Int, 20, 525-8.

ROENNEBERG, T., WIRZ-JUSTICE, A. & MERROW, M. 2003b. Life between clocks: daily temporal patterns of human chronotypes. J Biol Rhythms, 18, 80-90.

URBÁN, R., MAGYARÓDI, T. & RIGÓ, A. 2011. Morningness-eveningness, chronotypes and health-impairing behaviors in adolescents. Chronobiol Int, 28, 238-47.

WATERHOUSE, J., EDWARDS, B., NEVILL, A., CARVALHO, S., ATKINSON, G., BUCKLEY, P., REILLY, T., GODFREY, R. & RAMSAY, R. 2002. Identifying some determinants of “jet lag” and its symptoms: a study of athletes and other travellers. Br J Sports Med, 36, 54-60.