Category Archives: Annual theme

Early to bed and early to rise… makes a teen healthy, wealthy and wise? (Part 2)

By Gaby Illingworth, Rachel Sharman & Russell Foster; @OxTeensleep, @gabyillingwort1, @DrRachelSharman, @OxSCNi

To the possible dismay of parents hoping to start the family day bright and early, teenagers hit the hay and wake up at increasingly later times during adolescence – a delay of between one and three hours compared to pre-pubertal children.

Teenagers struggle to fall asleep early but still need to wake up for lessons during the school week, which contributes to a reduction in time spent asleep. At the weekend, the morning hours may well be spent snoozing to “catch-up” on lost Zzz’s.

In 2015, the National Sleep Foundation recommended that teenagers, aged 14 to 17 years, should be getting eight to ten hours of sleep a night. However, across the globe, teenagers are routinely not getting enough sleep, with older adolescents more likely to have insufficient weekday sleep than early adolescents. One of the consequences of insufficient sleep is that sleepiness during the day is common in this age group.

Sleep researchers have suggested some mechanisms behind this change in teenagers’ sleep timing.

How teenagers become owls: slower clocks, increased light sensitivity, or decreased sleep pressure

Although we don’t know why adolescent sleep changes, we do know that changes occur in the two processes which govern sleep – the circadian rhythm and sleep/wake homeostat. (Catch up on these two concepts in our previous post.)

The teenage biological clock has been proposed to run more slowly at this age, driving their sleep timing later, meaning their chronotype becomes more owl-like.

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From DIVA007 on Flickr

Another suggestion is that their biological clock might be more sensitive to light in the evening (delaying sleep) and less sensitive in the morning (making them wake up later).

Adolescent sleep pressure is also thought to accumulate more slowly during the day, making them less tired when they reach the evening.

Jetlag without leaving the country

We know what jetlag feels like when we travel across time zones. Our internal time takes a while to adjust to the new external time.

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Teenagers experience something similar with ‘social jetlag’: when their internal time (chronotype) is misaligned with social time (school commitments). At the weekend, they are more likely to be able to sleep according to their chronotype than during the school week. This misalignment of sleep/wake timing has been shown to associate with poorer cognitive functioning.

To blame the bright screens or not?

Teenagers’ lack of sleep is not all down to physiology. They, just like adults, may be engaging in behaviour that isn’t conducive to sleeping well.

The effect of light exposure on sleep has received increasing attention with the proliferation of electronic device use in recent years. However, the results are mixed.

One study on young adults asked individuals to read an e-book at maximum intensity under dim room light for around 4 hours (18:00–22:00) before bedtime on five consecutive evenings, whilst the control group read a printed book.

While the study concluded that those that read the e-book took longer to fall asleep, had lower morning alertness, and a delay of the circadian clock compared to reading a printed book, the effects were relatively small. Those participants who read e-books took only 10 minutes longer to fall asleep (Chang et al., 2015).

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As a result, some caution needs to be exercised when the press reports that reading an e-book before bed has unintended biological consequences that may negatively affect performance, health, and safety.

Nevertheless, the impact of using electronic devices prior to sleep does seem to be important. In a large US survey, adolescents were shown to have increased the time spent using electronic media devices from 2009 to 2015.

This was correlated with a decline in sleep duration (Twenge et al., 2017), and light from such devices has been blamed. Such studies have encouraged the use of in-built or downloadable applications that can dim the brightness of screens and/or reduce the light emitted.

Light interventions are now being considered as a tool for adolescents experiencing difficulties with sleep, including reducing their exposure to evening light and increasing morning light to advance the clock to a time more suited for school.

Unfortunately, the evidence showing that such interventions can be helpful is lacking. Furthermore, it is important to stress that game use, social media, and watching TV are all likely to be cognitively arousing so teens may simply feel like staying up when they use electronic media devices.

As a result, disentangling the light effects versus the alerting effects of devices is complex and awaits good experimental studies.

Highly caffeinated

 

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From Austin Kirk on Flickr

Caffeine is a stimulant with a half-life of approximately six hours in healthy adults (meaning that half of it is broken down in our bodies in six hours). It works by preventing the molecule adenosine, which promotes sleep, from having its effect in the brain, thus promoting wakefulness.

Teenagers are advised to consume no more than 100mg of caffeine per day, yet highly-caffeinated energy drinks are popular among teens. Many energy drinks contain higher caffeine levels than 100mg in a single can. Consuming caffeine later in the evening, or consuming it excessively throughout the day may be another contributory factor to delayed sleep.

Correspondingly, the National Sleep Foundation 2006 ‘Sleep in America’ poll found that adolescents who drank two or more caffeinated beverages each day were more likely to have insufficient sleep on school nights, and think they have a sleep problem, than those who drank one beverage or fewer.

We don’t need no early morning classes

School-based interventions are now underway that aim to improve teenage sleep. Sleep education programmes inform teenagers about the lifestyle factors that may be affecting their sleep and how they can improve sleep hygiene.

There is also a movement to delay school start times to better suit the adolescent clock by giving teenagers the opportunity to sleep at hours more aligned with their chronotype and reduce their social jetlag.

Given all the research, one could suggest that “early to bed, later to rise, may help the teen be healthy, wealthy and wise” would be a better amendment to the age-old quote for our average teenager.


References

Chang, A.M., Aeschbach, D., Duffy, J.F. and Czeisler, C.A., 2015. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences112(4), pp.1232-1237.

Twenge, J.M., Krizan, Z. and Hisler, G., 2017. Decreases in self-reported sleep duration among US adolescents 2009–2015 and association with new media screen time. Sleep medicine39, pp.47-53.

Early to bed and early to rise… makes a teen healthy, wealthy and wise? (Part 1)

By Gaby Illingworth, Rachel Sharman & Russell Foster; @OxTeensleep, @gabyillingwort1, @DrRachelSharman, @OxSCNi

Teenagers are well-known for routinely staying up late and then having a long lie-in. Sometimes this is put down to laziness or their transition from childhood into ‘Kevin the Teenager’.

However, there are biological reasons which help explain why teenagers are late to bed and late to rise, and why they might not actually be getting enough sleep to make them healthy, wealthy, and wise.

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Created by Matteo Farinella

Sleep matters. A wealth of evidence supports the importance of sleep for our physical, mental, and emotional functioning. Insufficient sleep has been linked to problems with attention, creativity, memory and academic performance, as well as increased impulsivity, and difficulties with mood regulation.

Sleep: a double-act

Sleep is driven by two processes working in tandem: the circadian rhythm and the drive for sleep (sleep homeostat).

The circadian rhythm is a roughly 24-hour cycle of changes in physiology and behaviour, generated inside our bodies. These rhythms come from certain genes being turned on and off (called clock genes) in almost all cells throughout the body. The master clock, (the suprachiasmatic nucleus in the brain), coordinates the rhythms within these cellular clocks.

The second system involves a balancing (homeostatic) process. Put simply, the longer you have been awake, the greater the need for sleep will become. The drive for sleep is thought to stem from a build-up of various chemicals (in the brain) while we are awake. For example, adenosine is a building block of our body’s energy currency (ATP), so it builds up as a consequence of energy use in the brain. Adenosine inhibits wake-promoting neurons and stimulates sleep-promoting neurons. As we sleep, adenosine is cleared and sleep pressure reduces.

Sometimes the two systems oppose each other. For example, we would feel very sleepy mid-afternoon due to increasing sleep pressure if it were not for the circadian drive for wakefulness.

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Sleep occurs when the circadian drive for wakefulness ends and the drive for sleep kicks in. Then when the ‘sleep debt’ you have accumulated during the day has been re-paid (and so sleep pressure is reduced), and the circadian drive for wakefulness is sufficiently strong, we wake up.

Why some people don’t like mornings

Some of us love to burn the midnight oil, while others schedule in regular morning runs. The technical term for your preferred sleep/wake timing is chronotype, what we colloquially refer to as being an owl or a lark. You are owl if your biological clock runs slower and a lark if it runs faster.

We don’t run on 24 hours

While our day runs on 24 hours, for most of us, our internal clocks don’t. Therefore, our internal clock needs to be adjusted daily by external time cues such as light intensity. The master biological clock receives light signals direct from cells in the retina, which are most sensitive to blue light.

Dusk triggers the production of melatonin (the ‘vampire hormone’). Although not a sleep-inducing hormone, melatonin serves as a cue for rest in humans, with levels increasing as we approach sleep and remaining high during the course of the night.

In contrast, dawn light suppresses melatonin levels. The circadian clock responds differently to light depending on the timing of exposure, so that morning light advances the clock (making us get up earlier) and evening light delays the clock (making us get up later the next day).

As well as playing a role in sleep regulation via the circadian clock, light affects how alert you feel. You may have noticed that bright light increases your alertness, so relatively bright light before bedtime will increase the likelihood that you will feel sleepier later.

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Stay tuned for next week’s blog about how changes in these systems affect teenage sleep.

Exercise, stress and Star Wars: Best of 2017 roundup

Happy New Year! In 2018, we look forward to more physiology fun, and to giving you an insight into the exciting new developments in the Science of Life!

Physio-what, you ask? Take a look at our animation below introducing physiology! Scroll down to find out more about a centuries-old shark patrolling the deep Arctic Ocean, how being active gives children’s hearts a head start for life, and why it’s time scientists took back control from exercise gurus, in our best of 2017 roundup!

1. Exercise scientists should fight the exercise gurus

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Exercise gurus build strong rapports with their audience to encourage commitment, but they will often simplify a large body of scientific evidence to back up their advice.

In this post, Gladys Onambele-Pearson and Kostas Tsintzas discuss the risks of letting exercise gurus disseminate exercise science to the public, and why it may be time for scientists to become the actual celebrities.

2. The Myth of a Sport Scientist

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There is a mismatch between the perceptions and reality of what a sport scientist is and what skills this career entails: just because exercise scientists use models of sport performance, exercise bouts or physical activity sessions, doesn’t mean that there aren’t complex scientific skills, theories, analytics and techniques behind the work.

Read more from sport scientist Hannah Moir in this post.

3. Shark Diary, Episode I: On the trails of the Greenland shark

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How do you keep lab chemicals cool when there’s no fridge in your room? Well, if you’re in chilly Denmark, you could just hang them outside your window.

Holly Shiels did just that in Copenhagen, on her way to Greenland to join a team of physiologists on a shark research mission. Their aim was to gather data on the physiology of the Greenland shark. Clarifying how these animals reach hundreds of years of age without developing diseases associated with human ageing, like cancer and heart disease, could lead to new therapies down the line, and understanding shark physiology is also important for their conservation.

Read more about the mission in this post, and check out watch below to see the researchers braving the icy waters of the North Atlantic and releasing a tagged Greenland shark.

4. Breath of the Sith: a case study on respiratory failure in a galaxy far, far away

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Have you always wondered what actually is going on behind the mask? Darth Vader’s acute respiratory failure appears to be the consequence of a number of factors, including direct thermal injury to the airways, chemical damage to the lung parenchyma caused by inhalation of smoke and volcanic dust particles, carbon monoxide poisoning, as well as secondary effects to his severe third degree burns, which seems to cover ~100 % of his total body surface area.

Read on as Ronan Berg and Ronni Plovsing make a tongue-in-cheek diagnosis of the numerous respiratory ailments of everyone’s favourite Sith Lord.

5. Exercise now, thank yourself later

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Exercise is good for the heart, but the benefits fade soon after we stop training… or so we thought. Studies so far have focused on adults, but research published last November in The Journal of Physiology reveals that exercise in early life could have lifelong benefits for heart health.

This is because young hearts are able to create new heart muscle cells in response to exercise, an ability that is mostly lost in adulthood. Glenn Wadley, Associate Professor at Deakin University and author of the study, explains the findings in this post, and makes the case for children to get active!

As if that wasn’t enough reason to exercise, being active is one of three tips that can help relieve the stress we feel for instance at the approach of exams. Watch our animation below to find out more about what stress does to our bodies, and start making good on those New Year resolutions!

Stress and the gut – it’s not all in your mind (Part 2)

By Kim E. Barrett, Division of Gastroenterology, Department of Medicine, University of California, San Diego, USA, @Jphysiol_eic.

This article originally appeared in our magazine, Physiology News.

The numerous microbes living inside of us help break down nutrients and “educate” our immune system to fight infection, but how do they help us respond to stress?

The microbiota as a mediator of responses to stress

Gut microbes change when people have intestinal diseases, such as inflammatory bowel diseases and irritable bowel syndrome. Indeed, some of the characteristics of these diseases can be transferred to animals in the lab that lack microbes, using microbes from diseased mice or humans. It is also becoming increasingly clear that gut microbes and their products may have effects well beyond the confines of the intestine itself.

Perhaps the most intriguing aspects of this area of research is that which ties the composition of the gut microbiome to brain function and the brain’s response to stress. Further, the adverse effects of stressful situations on gut function depend on the presence of intestinal microbes. To date, research supports bi-directional communication between the gut and brain (pictured below) that influences the normal function of both bowel and brain alike. This may explain, for example, why some digestive and psychiatric disorders go hand-in-hand (Gareau, 2016).

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Bi-directional communication between the gut and brain.

Evidence in human patients largely shows correlation not causation so far. Still, it is intriguing to observe that derangements in the microbiome have been associated with many conditions, including depression, autism, schizophrenia and perhaps even Parkinson’s disease (Dinan & Cryan, 2017).

Therapeutic manipulation of the microbiota – from probiotics to transplants

So if both intestinal and neuropsychiatric conditions are potentially caused by changes in the gut microbes (at least in part), and if such alterations also mediate the impact of stress on the relevant organ systems, can we mitigate these outcomes by targeting the microbiota?

Several approaches have been posited to have either positive or negative effects on the make-up of the gut microbiota and its intestinal and extra-intestinal influences.  Perhaps the most obvious of these is the diet. While the gut microbiota was at one time felt to be relatively immutable in adulthood, improved  techniques indicate that its make-up, in fact, is profoundly influenced by the composition of the diet and even by the timing of meals. For example, Western diets, high in meat and fat, decrease the diversity of the microbiota (and may even promote the emergence of pathogenic properties in commensals), whereas diets rich in plant-based fibre increase it.

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Another approach to targeting the microbiota is the use of antibiotics, although for the reasons discussed in Part 1, these are likely to be mainly deleterious, particularly early in life. The composition of the microbiota can also be altered directly by the administration of probiotics, which are commensal microorganisms (the host benefits, while the microbes are unaffected) selected for their apparent health benefits that can be taken orally.  Studies in animal models demonstrate that probiotics can improve both gut and cognitive function in animals exposed to a variety of stressors, or can negate the cognitive dysfunction accompanying intestinal inflammation or infection.  However, not all probiotics are created equal, and much work remains to be done both to validate animal studies in human clinical trials, and to define characteristics of probiotic strains that predict efficacy in a given clinical setting.

Perhaps the approach to targeting the microbiota that has attracted the most recent public attention is the practice known as faecal microbial transplant (FMT), where faecal material is transferred from a healthy donor (often a relative) to someone suffering from a specific intestinal or extraintestinal disease.  Enthusiasm for FMT derived initially from its dramatic efficacy in some patients suffering from disabling and persistent diarrheal disease as well as other symptoms associated with treatment-resistant infections by C. diff (a harmful bacteria).  More recently, there have been encouraging data suggesting that FMT may be effective in producing remission in inflammatory bowel disease, although the long-term consequences are unknown, and larger, well-controlled studies are needed.  Exploratory reports even suggest beneficial effects of FMT on gastrointestinal and behavioural symptoms of autism, or in obesity and metabolic syndrome (a cluster of conditions that occur together and increase your risk of heart disease, stroke and other conditions), but much further work is needed to validate these preliminary data.  Ideally, FMT procedures should be conducted under carefully-controlled and physician-supervised conditions to screen for the potential presence of pathogens or toxins.  Nevertheless, despite the obvious “yuck” factor, “do-it-yourself” instructions can readily be found online (there are even Facebook groups), and some individuals are sufficiently distressed by their condition to give it a try.

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Yep, this is exactly what you think it is.

Mitigating negative effects of stress

In conclusion, it is clear that our response to stress, whether manifested in our thought patterns or in our gut, is dramatically shaped by the microbiota that resides in the intestines.  Particularly in humans, studies conducted to date have largely been confined to cataloguing the key players in a given setting, but animal data are provocative, and studies focusing on microbes’ roles and functions in humans will doubtless follow.   No matter what, in the coming years, the explosive growth of studies aiming to target the microbiota for health benefits should give us a much better understanding of which approach, if any, is likely to be most beneficial for a given condition and even a given individual, since host factors clearly can also impact our microbial composition.  This work holds the promise of ameliorating negative effects of stress, and perhaps may offer new avenues for the therapy or even prevention of the myriad of stress-related disease states that are increasing in incidence in developed countries.


References

Dinan TG & Cryan JF. (2017). Gut instincts: microbiota as a key regulator of brain development, ageing and neurodegeneration. The Journal of physiology 595, 489-503.

Gareau MG. (2016). Cognitive function and the microbiome. International Review of Neurobiology 131, 227-246.

 

Stress and the gut – it’s not all in your mind (Part 1)

By Kim E. Barrett, Division of Gastroenterology, Department of Medicine, University of California, San Diego, USA, @Jphysiol_eic.

This article originally appeared in our magazine, Physiology News.

We all know that stress has an impact on the function of our digestive system. Whether it is the transient butterflies that accompany an exam or an interview, or the more toxic consequences of chronic stress, our experience of our world and its challenges can profoundly alter our digestion, absorption of nutrients, and excretion.

What has been less fully appreciated, until recently, is that communication between the brain and gut is bi-directional. Gut illnesses may be accompanied by brain disorders, such as anxiety, depression, and memory problems.  The brain and spinal cord are in constant communication with the gut, in part via the “little brain” – the nerves present in the gut that communicate with the brain.

While we humans like to think that we are masters of our own universe, in fact we, along with all other beings, are superorganisms. Our bodies consist not only of our own cells and genome, but also of distinctive populations of ‘friendly microbes’, along with their genes and ability to break down compounds. This so-called “microbiome” is made up mostly of bacteria, the best-studied populations, but also other microbes such as fungi and viruses (which are only now beginning to be examined).  Specialized groups of microbes inhabit various parts of our body, such as the intestines, mouth, skin, lungs, and genitals. The most extensively characterized of these microbiomes is the collection of bacteria in the gut, consisting of thousands of species in a typical healthy human adult. They reside throughout the intestines, but are most heavily concentrated in the colon. There are as many as 1014 of them throughout the gut. That’s ten times the number of human cells in the entire body (Sekirov et al., 2010). Recently, the 10:1 ratio has been disputed, with a claim that the numbers of human cells and gut bacteria are of the same order of magnitude (Sender et al., 2016). Even if this true, the microbes collectively have more genes than our cells do.

We are rapidly learning the ways in which these gut microbes may be important mediators of the cross-talk between the gut and brain. They are, in turn, influenced by environmental conditions, such as stress and diet, in ways that change their impact on both our thinking and digestion.

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Friendly microbes – what do they do for us?

Microbes, in the gut or elsewhere, are not essential for life, as illustrated by the ability to raise animals in a sterile environment in the lab. Nevertheless, the gut microbes in particular offer several advantages to the organism they inhabit. For us, they break down nutrients we can’t, such as dietary fibre, drugs, carcinogens, and compounds that break down into vitamins.  Similarly, the microbiota “educate” the immune system of organs such as our lungs and intestines to fight foreign substances but tolerate the proteins of broken-down food or other harmless microbes.

The organisms of the microbiome also defend against pathogens by crowding them out, producing substances that kill bacteria or keep them from reproducing, or causing the host to create those lethal compounds itself. For this reason, antibiotics that kill beneficial microbes can render patients susceptible to intestinal infections and overgrowth of harmful bacteria, such as Clostridium difficile (C. diff).

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3D cellular model of an intestine by Ben Mellows, PhD Student, University of Reading, UK

Gut microbes and birth

We think that gut microbes exist in the body immediately after birth, although some controversial data suggests the presence of microbes in the fetus before birth. Animals without microbes can be born via Caesarean section (C-section), implying that even if there are microbes in the womb, organisms don’t need them to survive (Perez-Munoz et al., 2017).

For babies delivered vaginally, their gut microbes are initially very similar to the mother’s vaginal microbiota, whereas they differ substantially for babies delivered by C-section. An intriguing recent study partially restored “normal” microbes in the gut, mouth, and skin by exposing babies delivered via C-section to the mother’s vaginal fluids. The authors thought that this might reverse the known association between C-section deliveries and an increased risk for immune and metabolic disorders (Dominguez-Bello et al., 2016).

For the first year or two of life, the baby’s microbes are relatively simple and variable, but they gradually take on the characteristics of a mature, adult-like microbiome. These early years are also a critical period for maturation of the immune system, so it makes sense that disrupting the maturation of the infant’s microbes also predisposes them to autoimmune and allergic diseases. For example, the increasing tendency to protect babies from germs or an excessive early-life use of antibiotics may set them up for an increased later risk of asthma, metabolic disease or obesity. This is called the “hygiene hypothesis” (Schulfer & Blaser, 2015).

Stay tuned for the part 2 of the series next week to learn about how gut microbes respond to stress, and the efficacy of therapeutics, from probiotics to transplants.


References

Dominguez-Bello MG, De Jesus-Laboy KM, Shen N, Cox LM, Amir A, Gonzalez A, Bokulich NA, Song SJ, Hoashi M, Rivera-Vinas JI, Mendez K, Knight R & Clemente JC. (2016). Partial restoration of the microbiota of cesarean-born infants via vaginal microbial transfer. Nat Med 22, 250-253.

Perez-Munoz ME, Arrieta MC, Ramer-Tait AE & Walter J. (2017). A critical assessment of the “sterile womb” and “in utero colonization” hypotheses: implications for research on the pioneer infant microbiome. Microbiome 5, 48.

Schulfer A & Blaser MJ. (2015). Risks of antibiotic exposures early in life on the developing microbiome. PLoS Pathog 11, e1004903.

Sekirov I, Russell SL, Antunes LC & Finlay BB. (2010). Gut microbiota in health and disease. Physiological reviews 90, 859-904.

Stressing out the immune system

Excerpt from a Physiology News feature by Natalie Riddell, School of Biosciences and Medicine, University of Surrey, UK, @N_Riddell_Immun

Natalie Riddell LatitudeStress can get under our skin. It can influence each and every physiological system, and all of the major contemporary diseases in the UK, including cardiovascular disease, inflammatory disorders, metabolic syndrome, infectious diseases and cancer, have been associated with stress. Stress affects everyone, and levels of anxiety and mental health disorders are increasing with work-related stress now being the second most commonly reported illness in the UK workforce. Over the last four decades, research in the area of Psychoneuroimmunology (PNI) has identified stress induced immune alterations as a potential mediator between chronic stress and ill-health.

In the 1970s, Holmes and Rahe developed a scale to subjectively grade stress, [which inspired our recent survey of stress in modern Britain]. They ranked over 40 different types of life stressors, such as the death of someone close to you, changes in relationship status, work-related stress, even Christmas, and they assigned each stressor a score. The total tally of stress scores that a person had experienced in the last year could accurately predict the likeliness of future illness. This demonstrated that stress and illness were closely related. In the 1990’s, Cohen et al., eloquently demonstrated that psychological stress increased the rates of respiratory infections and clinical symptoms in participants inoculated with the common cold (Cohen, Tyrrell et al. 1993). Subsequent studies revealed that every organ, tissue and cell of the immune system could be altered by psychological stress. The involvement of immune alterations in stress induced diseases was recognised and the field of PNI was born.

Defining stress

Stress is highly subjective. Something that I may class as stressful (watching Arsenal this season), may not be stressful to other people (Tottenham supporters). So how can we define stress? In the 1960s, the psychologist Richard Lazarus introduced the concept that stress is a process consisting of three distinct steps. First, a stimulus (i.e., the stressor) has to be present and perceived. Second, the stimulus initiates a conscious or sub-conscious process whereby the stressor is evaluated in relation to available coping options. If the demands of the situation exceed the ability to cope, then the situation is perceived as stressful. Thirdly, this results in a stress response involving emotional (e.g., anxiety, embarrassment) and biological (e.g., autonomic-endocrine) adaptations. Put simply; stress is a situation or event that exceeds, or is perceived to exceed, the individual’s ability to cope, that then triggers an emotional and biological response.

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Image: Darryl Leja, NHGRI

The stress adaptation response and immunity

The biological adaptation to stress is activation of the sympathetic nervous system. The same biological response is induced whether the stressor is psychological, such as anxiety or embarrassment, or physical, for example, exercise, trauma or fever. In the case of psychological stress, the individual perceives an inability to cope and this results in the amygdala, a part of the brain that contributes to emotion processing, sending a distress signal to the nearby hypothalamus. The hypothalamus can communicate with the rest of the body via either of two arms of the involuntary nervous system: “rest and digest” (parasympathetic) or “fight or flight” (sympathetic). During stress, this “fight or flight” system is triggered and various physiological changes occur, including an increase in heart rate, respiration and energy production. This promotes survival of the individual by maximising physical capacity to cope with the stressor.

During stress, signalling from the “fight or flight” sympathetic nervous system causes the adrenal gland to secrete the two main stress hormones; adrenaline and cortisol. These hormones can spread and act throughout the body via the circulation. The sympathetic nervous system innervates all of the organs of the immune system, and individual immune cells can directly respond to changes in circulating levels of adrenaline and cortisol. Stress is therefore able to alter every process of immunity, from the initial development of stem cells into early immune cells in the bone marrow, through to the triggering of immune responses to specific antigens in the lymph nodes. Even when in the peripheral tissues, such as the skin or gut, where mature immune cells are most likely to encounter infections, the cells can be regulated by stress hormones. It is therefore unsurprising that the immune system is a modifiable target of stress.

Read Natalie’s full article in our magazine Physiology News to find out how acute stress changes the composition of the blood, and why our Stone Age brain can’t cope with the constant stress of modern life. Her feature takes a more detailed dive into the effects of stress on the immune system’s day-night (circadian) rhythm, and points to stress management as an easy and affordable way to make us healthier.

Reference

Cohen, S., D. A. Tyrrell and A. P. Smith (1993). Negative life events, perceived stress, negative affect, and susceptibility to the common cold. J Pers Soc Psychol 64(1): 131-140.

 

 

Getting stressed out at the Lancashire Science Festival

By Rachel Boardman, University of Nottingham, UK, @boardventures

Two weeks ago, I formed part of The Physiological Society’s team of enthusiastic volunteers in the Biology Big Top area of Lancashire Science Festival. Dressed to impress in our ‘I love physiology’ t-shirts, we were all set to engage our audience about the effects of stress on the body.

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After measuring a participant’s blood pressure and heart rate we would then expose them to either a mental or physical stress. The mental stress consisted of playing whack-a-mole – a version of the popular arcade game where you hit the mole when it lights up – while being asked maths questions. Evil, right?

I had a go, to errm test it out, and one of my fellow volunteers challenged me to count backwards from 100. Not so bad, I thought. She then added, “In 7s.”

“Oh errm.. 100, 93… errr…86. Yeah I’m out.”

A few of our participants were amazingly good at this (unlike me) while some heard the word maths and immediately opted for the physical stressor, the cold pressor test.IMG_2518

This involved sticking your hand in an ice-cold bucket of water for 1 minute (we toned it down to 30 seconds for the younger children because we’re not harsh). The shock on each participant’s face as they realised how cold the water actually was followed by the realisation that a whole 60 seconds doing this was far longer than they had realised. Most showed clear signs of discomfort, squirming and fidgeting in their seat, increasing their breathing rate and even providing a running commentary on just how they were feeling, but there were others that sat quite still with a wry smile on their face that said ‘this isn’t that cold’.

Once we had suitably stressed our victims participants out, we measured their blood pressure and heart rate again. What would you expect to happen?DEcsbysXUAAdU07.jpg

Well, if you know anything about science, then you will know that it doesn’t always go to plan. That is precisely what happened to us. The majority of people’s blood pressure and heart rate did increase. However, we also had participants who seemingly reacted to these stressors by relaxing, or for whom only blood pressure or heart rate changed. That’s science, guys!

Read Rachel’s full article on her blog, The Boardventures.