Stress: From Saviour to Killer
Stress is everywhere. We have stressful jobs, get involved in stressful situations and people stress us out. You might have stressful days or stressful weeks. Indeed, many people report feeling stressed constantly. Unless you shut yourself off from all media (and more of that in Chapters 6 and 9) you cannot escape the fact that ‘stress’ in various guises is making us ill and it is becoming increasingly obvious that our lifestyles are to blame. But how can our comfortable and safe modern lives possibly be more stressful than those our ancestors faced? I haven’t wrestled any bears or survived any famines lately and in all likelihood neither have you. Why then does the comfortable, technologically enhanced modern world that we have so assiduously created to make life more bearable and luxurious cause us ‘stress’?
The word stress is used in all sorts of scenarios when we feel under pressure, rushed or otherwise frazzled by the demands of modern life. However, the true meaning of the term, and its medical implications, is far more subtle than the headlines would have us believe. By examining what stress actually is, as opposed to what click-bait headlines might have us believe it is, we can start to understand stress, how it’s affecting our health, how and why it evolved and how our modern lives interact with this evolutionary heritage in such negative ways.
The implications of stress in the modern world go far beyond intellectual curiosity over evolutionary mismatches. Stress is a killer. It is possible for acute stress to cause heart attacks, as shown by a rather elegant if morbid ‘natural experiment’ in Athens following a large earthquake in 1981. Researchers examined records of deaths in the days following the quake on 24 February 1981 with records of deaths that occurred in a similar period in the year before (1980) and the year after (1982). They found more cardiac-related deaths than expected in the days after the earthquake but no effect on deaths related to cancer, and little if any increase in deaths from other causes. The ‘excess mortality’ identified in 1981 was more evident in people with underlying heart disease and the clear conclusion was that stress caused by the earthquake had triggered heart attacks, especially in those with conditions that left them vulnerable.1 Sudden death from cardiovascular problems has been shown in the aftermath of other quakes in Australia and California, underpinning one simple fact: acute stress can be fatal.
Acute stress and heart attacks are at one end of the stress spectrum, and the fact that you could die at times of acute stress perhaps comes as no surprise. The increase in the cardiovascular diseases that often underlie such stress-triggered mortality are caused by our modern diets combined with a lack of exercise playing against a background of genetic susceptibility to such diseases in many people. This is a theme becoming familiar from earlier chapters and it shows an obvious mismatch between our evolved physiological responses to sudden, potentially dangerous events and the problems that a modern lifestyle causes for our cardiovascular health. It is, however, the medical effects of long-term, chronic stress that are especially worrying from a public health perspective and that are most affected by our recent lifestyle shift interacting with our evolutionary heritage. A constant drip-feed of relatively low-level physiological stress in response to pervasive ‘micro-stressors’ (a groaning email inbox, a missed bus, financial worries, children, relationship problems, an empty fridge, interest rates, climate change, Instagram, the laundry…) causes, as we shall see, the release of a range of chemicals within the body that collectively and cumulatively cause problems over the long term. Common physical effects of stress include headaches, muscle tension and pain, chest pain, fatigue, loss of libido, upset stomach and problems sleeping. Each of these physical effects cascades through to our mood and our behaviour and that in turn can create more stressors in an immensely harmful feedback cycle. Stress-induced headaches make us anxious, anxiety can trigger eating disorders, and pain causes restlessness, mood swings and self-medication through drug and alcohol abuse. Meanwhile, fatigue and sleep problems cause further anxiety and a sense of being overwhelmed that can lead to social withdrawal and yet more self-medication via the off-licence (Chapter 8). These spiralling stress symptoms have less immediately noticeable effects but they have been implicated in causing diseases like depression, Alzheimer’s and even, at least according to some headlines, cancer (but read on to see why those headlines can probably be ignored). As we shall see though, disentangling the potential connections between modern lifestyles, micro-stressors, disease and human evolution is far from simple. Before we get to that we must first answer a very important question – what is stress?
… But it keeps us alive
Animals, including us, like to operate in a state of constancy. We don’t generally like change and we especially don’t like major change that happens rapidly. The process by which a steady, favourable state is maintained in our bodies is called homeostasis and most of the time we can easily keep everything ticking over exactly as it should. Think of it like a thermostat turning the boiler on and off to regulate the temperature in your house. We don’t have to think about it and most of the time everything works smoothly.
Physiologically, stress is our response to an environmental challenge that pushes us outside of our normal, stress-free regulation; perhaps we fall into icy cold water or a tiger suddenly appears from behind a bush. When the environment changes suddenly, and for the worse, we must do something about it and do something quickly. Our normal processes simply aren’t going to work any more, and sitting back and hoping that things will magically return to normal is not going to fix the immediate and serious problem. We need to make things happen and the way we do this is by ‘stressing’. Stress is, at its most basic level, an evolved biochemical response to danger. And it’s very useful.
Fight or flight
We have a wonderful response to scary and life-threatening situations that operates entirely outside of our conscious control. It can cause us to wet ourselves, go pale and start shaking but, despite these unpleasant side effects, it can also save our lives. It is called the acute stress response, or more commonly ‘fight-or-flight’. In essence, our bodies get pumped up and ready to fight or flee. However, the details are more complicated than ‘we get pumped up’ and they are worth exploring because the more we understand how the fight-or-flight response works, the more we can start to appreciate the medical problems related to our stress response in the modern world.
Stress begins in the brain. Made up of a number of different discrete but interconnected physical structures, the brain is complex. It includes relatively well-known structures like the cerebellum, the hippocampus and the cortex as well as less well-known structures like the left and right amygdala (from the Greek word for almond, which they resemble) located deep in the brain. The amygdala are concentrations of nerve cells that are very closely linked to our emotions including happiness, sadness, anxiety and fear. It is here that sensory information, especially from our ears, eyes and sense of touch, is processed very rapidly and without our conscious input. If a threat is perceived, the amygdala begin an impressive and complicated set of reactions that cascade throughout the body. The reaction begins with a ‘we’re under attack!’ nervous signal sent to another part of the brain, the hypothalamus.
The hypothalamus doesn’t do much ‘thinking’ but instead acts as a link between our brain and the chemical messengers, hormones, which circulate in our bloodstream and control much of what goes on in our bodies. When we get scared, the hypothalamus kicks into overdrive and activates the sympathetic nervous system. Operating entirely unconsciously, the sympathetic nervous system’s primary job is to coordinate our fight-or-flight reaction. Once stimulated by the hypothalamus, it causes us to speed up, tense up and become more alert. These are great responses to an immediate danger. They prepare us to kick some ass or, as is usually the best plan, to run away.
As well as activating ‘superhero mode’, the hypothalamus sends out signals to turn off the muscles moving food through our digestive system (no need to waste energy on systems that won’t save our life) and to make blood vessels contract (hence we go pale). At the same time, nervous signals stimulate our adrenal glands, pyramid-shaped organs that lie on top of our kidneys. Once the adrenal glands are stimulated they start rapidly producing adrenaline and noradrenaline (and we are talking milliseconds here since we have no time to lose). This pair of ‘stress hormones’ causes, among other effects, our heart rate and blood pressure to increase rapidly. We tend to think of hormones as ‘slow’, perhaps because we commonly think of them in relation to things like puberty, sex drive and the menstrual cycle, and nervous signals as ‘fast’ and although that is technically true (nervous signals are conducted through the body far more rapidly than chemicals can be circulated) the endocrine system is far from sluggish when short distances are concerned.
Meanwhile, the hypothalamus is messaging the pituitary gland to release another hormone, adrenocorticotropic hormone (ACTH), that again passes rapidly through our bloodstream and stimulates the adrenal glands even further. This additional stimulation causes them to release a heady mix of yet more hormones, including one that will crop up quite frequently in this chapter, cortisol. All of this frantic activity serves but one purpose: to hype the body up into a state where we can get ourselves out of an immediately life-threatening situation. Make no mistake, seeing that tiger jump out from behind a bush causes profound changes to our body, and thanks to evolution we might just make it out alive. It is probably fair to say that this remarkable and complex interaction between the nervous and endocrine (hormone-producing) systems kept our ancestors alive long enough to have the offspring that form the chain all the way to us. That ‘stress-thankful’ chain could be very long indeed. Some kind of fight-or-flight response mediated by adrenaline and related hormones is found in a remarkably wide variety of animals, including reptiles and amphibians as well as invertebrate groups like molluscs and insects,2 neither of which form part of our lineage but you get the idea – stress responses are more or less ubiquitous.
The harmful effects of stress
Words that have a precise meaning scientifically or medically, but are also used in broadly similar ways in everyday life, are hugely problematic for scientists and non-scientists alike. A fine example of this is the seemingly innocuous word ‘theory’. In everyday language, ‘theory’ promotes a sense of unsureness, of speculation, or of some ivory-towered notion that is unlikely to translate to the real world. ‘It’s all theoretical’ is almost an insult, suggesting some naive and unworkable idea. In science on the other hand, theory means quite the opposite. A theory is a robust and evidenced framework to explain something that is based on a set of well-supported and interlinked principles. The use of this term in connection with evolution in particular causes huge problems. Those who seek to undermine the foundations of modern biology will often stand on the side-lines hurling in the phrase ‘but it’s only a theory’, as though that somehow negates the huge deluge of evidence that is contrary to their deeply held belief. Likewise, stress has multiple meanings that go beyond the biomedical neuro-hormonal response to danger. Initially, stress was used as a medical term because of clear analogies with the stress (and also ‘strain’, another word with medical and everyday meanings) undergone by materials like a bridge girder as forces are applied. Even before we had the pathways involved in the stress response nailed down though, and before stress had a precise defined biomedical definition, doctors were clearly aware that the pressures of life had some implications for health. In a wonderfully titled paper from 1919, ‘The influence of psychic acts on the progress of pulmonary tuberculosis’, a Japanese medical scientist called Tohru Ishigami concluded that anxiety (‘psychic acts’, or as we would now call it, stress) caused by an overtaxing education system was causing a high mortality among young people with tuberculosis. In other words, children with TB were dying not because of the TB but because of the additional burden that TB put on their systems as they attempted to navigate the stressful Japanese education system.3 This startling conclusion, a warning perhaps for those with interests in education policy, was no flight of fancy. Ishigami, in an integrative, cross-disciplinary study that was well before his time, linked together laboratory research on guinea pigs, rabbits and rats, and epidemiological data on tuberculosis in Japan with developing research by Walter Cannon. Cannon was the scientist who invented the term homeostasis and also coined the phrase ‘fight-or-flight’. By combining some of Cannon’s early work on the biochemistry of the stress response with his own findings, Ishigami was able to start to piece together and produce evidence for the influence of stress on our health. Ishigami started on a quest that has continued apace over the century that has followed.
The harmful aspects of the stress response can be divided into acute and chronic. We’ve already seen the effects of acute stress in the Athens earthquake study. The sudden deluge of stress hormones triggered by emotional or physical stress causes increased heart rate and blood pressure, and in those with a healthy heart these increases enhance our ability to fight or flee. A good thing in many people, of course, but in those people with underlying conditions affecting the heart, such as coronary heart disease (where the blood flow supplying the heart muscle is restricted), the sudden increase in demand placed on the heart by stressful situations can prove fatal. For this reason, in addition to the usual ‘sensible quartet’ of not smoking, eating a healthy diet, drinking alcohol in moderation and exercising, medical advice now acknowledges the problem of stress and makes suggestions that even 10 years ago would have felt slightly more Glastonbury than Harley Street. As well as the rather obvious advice of ‘Avoid situations that you know will cause stress’ comes, for example, recommendations that ‘Quiet time, meditation, prayer, reading, yoga, and relaxation techniques can help in stress management’.
To appreciate the role that chronic stress plays in many of our lives we need to consider a ‘typical’ modern life. In particular, we need to examine closely those aspects of our lives that can be categorised as ‘modern’ and consider whether these aspects are resulting in a mismatch between our twenty-first-century lifestyle and our past evolutionary environment.
Defining a typical modern life isn’t going to be easy because we all live different lives. If we take a broad-brush approach though, it is possible to assemble some of the components common to many people’s lives and thereby come up with a typical day that includes at least some of the stressors present now that would not have been an issue to even our reasonably recent ancestors. Given we cannot go back in time, we are faced with a slight problem because we need a suitable group with which to compare our typical modern life. It is tempting (indeed, I have already been tempted in Chapters 2 and 3) to take extant hunter-gatherer tribes as our comparison group. Although this is a sound approach in some respects, it would be a mistake to assume that somehow these groups represent modern humans ‘minus 12,000 years or so’. The Sān people of Namibia, for example, are very much modern humans and although their lifestyle is more representative of a ‘simpler’, pre-modern lifestyle that does not mean that the people themselves represent some pre-modern human. It is possible to tie yourself up in knots over this type of comparison, and many have, but as we’ll see my analysis of a modern lifestyle gives a rather easy escape from an argument that can start down a path no one wants to tread. That get-out-of-jail-free card is provided by the simple fact that many of our modern micro-stressors are either a direct or an indirect consequence of technology that wasn’t (and isn’t) a part of a pre-modern lifestyle, whether that is one lived now or 12,000 years ago.
For the purposes of determining some of the stresses of modern life, I am going to bundle together differences between men and women to create a single ‘human’ lifestyle. I know this is problematic but it is also worth saying that as well as sex, stressors will differ with age, where you live, your background, your job and many other factors; detailing everyone’s lives is going to be, well, too stressful. With these caveats and cautions in place, let’s begin to map a typical twenty-first-century ‘modern lifestyle’ day. If your day is different from this, and I sincerely hope that it is, then with any luck you will still recognise some of the themes that develop.
6.30 a.m. Wake up 30 minutes before the alarm goes off worried that the alarm won’t go off because your phone will have decided to update overnight and wipe your alarm settings when it restarts. Or the phone will have mysteriously consumed almost all of the 100 per cent battery charge you gave it yesterday evening. Ponder whether you should keep the phone plugged in all night despite the small fire risk and some complex information about battery ‘memory’ that you half-read yesterday. And if you have the sound turned down for notifications and calls does that affect the alarm? Drift quickly back into a far deeper sleep than you managed during the night.
7.00 Woken by an annoying and loud alarm from a dream involving being unable to dial a phone number correctly, the consequences of which are too ghastly for your now partly awake brain to formulate in any sensible way. ‘How much sleep did I have? Was it enough? Am I getting the seven to eight hours recommended by the latest Facebook post that I’ll be reading in approximately one minute…’
7.01 Turn on phone. Spend the next 15 minutes blearily ‘catching up’ on 78 WhatsApp messages from a group of friends arguing over which Star Wars film is best, social media notifications involving the birthdays of some people you don’t actually know and ‘BBC Most Read’ news items. Learn that there has been a hurricane that has killed hundreds of people in a place you have never heard of and that a family you’ve never met has died in a fire in a city that you’ve never visited. Find out that a celebrity you have never heard of who is famous for being in a ‘scripted reality show’ (seriously, a what?) you have never watched has split up with someone else you don’t know who is largely famous for having sex with someone in another reality show you didn’t watch. Despair at the state of the world and end up mistyping a tweet in which you mean to say that the ‘world is shallow and superficial’ but somehow end up typing that the ‘worm will swallow and is super special’. Copy the tweet to avoid retyping the rest of it, then delete the tweet and then repost the tweet correctly after three attempts. There is still a typo.
7.20 Children wake up. At this point, if you have children you will understand and if you don’t then you won’t. And of course society gives you plenty to stress about if you don’t have children because apparently that is now everyone else’s business. Why don’t you have children? Do you want children? Why don’t you want children? Are you trying hard enough to have children? Have you eaten enough zinc? Is your childless situation selfless or selfish? There’s really no let-up.
7.20–8.30 A terrible blur of breakfast during which you can worry that the cereal you are pouring is too sugary and lacks nutrition, that the milk you bought at a rock-bottom price is destroying farmers’ lives, that the bread you are eating has come from an agricultural system that is crippling the environment and contributing to the sixth great extinction, or that the one beacon of hope in your morning, a cup of freshly brewed coffee, is going to give you cancer. You decide to check the latest findings on the whole coffee-cancer thing on your phone and wish you hadn’t. You brush children’s hair, a terrible experience for both brushed and brusher. About to leave, late, you realise teeth haven’t been brushed. Cue a massive rush to brush teeth so that tooth decay doesn’t set in and ruin your children’s smile for ever.
8.35 Run to car. It’s low on fuel (that is causing climate change of course) but, hey, there’s got to be enough in there for a few miles, right? There’s a weird rattle… turn up the radio to block it out, and of course you can hear more about that hurricane destroying thousands of lives. Great.
8.40 Be informed by all-knowing children in the back that it is World Sausage Day and that the school is having a ‘dress like a sausage’ fancy dress day, a fact apparently conveyed to all parents the week before via a message on some online forum that you are literally hearing about for the first time right now. Oh, and everyone needs pound coins for the charity donation that is required for fancy dress. Of course they do, because it’s not enough to pay taxes and give to charities you support, you also have to donate to charities you don’t necessarily agree with so that your children can take part in some activity that doesn’t in all honesty seem to enhance their education. You realise that what started as an inner monologue is now very much an outer monologue that is beginning to unnerve the children.
8.45 Somehow you improvise a serviceable fancy-dress outfit from the detritus that has collected in the boot of the car. A victory for untidiness. Likewise, you scrabble together enough change to fool the casual observer that it covers the donations required, when in fact it is 7p short, not including two foreign coins and a washer that may or may not be part of the seat-reclining system.
8.50 Drop off children at school, an operation that requires a mixture of precise but hugely aggressive driving and split-second door-opening accuracy. It is not for the faint-hearted…
8.55 Fuel light now on. Pull in to petrol station. Ignore signs and check email on phone while gesturing to an attendant, who is achieving the impossible feat of simultaneously both looking and not looking at you, to reset the pump from the previous customer. Eventually fill up with fuel. Decline three increasingly desperate offers to upsell your petrol, including a chocolate bar the size of a table top and a multi-tool that will break on its first deployment.
9.00 Email alerts start tumbling in.
9.30 Arrive at work to spend an hour and a half doing little but answering emails in a futile attempt to achieve the mythical ‘zero inbox’. Steadily come to realise that email is a beast of its own making and that the only way to stop it is not to send any. Continue to send emails…
11.00 Sit in a meeting that you know from the start will achieve nothing. Minutes are taken; hours are wasted.
13.00 Meeting ends having achieved nothing. You go to the canteen and after examining the caloric value of all the sandwiches you opt for a simple ham and cheese. With a sinking heart you realise you are shelling out more than 20 times the actual value of the ingredients and you make yet another pledge to make your own lunch, a pledge you know will never be honoured.
13.30 Slink off to gardens next door to grab a quick image for your Instagram account which you largely curate to show dreamy images of flowers and trees. You aren’t sure why but you get a little zing every time someone ‘likes’ a post.
13.40 Upload a fabulous image #nofilter. Wander back to work with the notifications already pinging.
14.00 Get call from school. Child has vomited. Marvellous.
14.45 Arrive at school wishing child could have waited to vomit until after school thereby allowing you to circumvent the 48 hours of childcare during the day you are now going to have to find. You hang around in the car park with a child smelling faintly of vomit until the others emerge.
15.17 Second child vomits in car in response to the vomit smell. Third child vomits in response to the sound of the second child vomiting. You now have ‘a situation’ that will have to be dealt with, ideally using bleach and heavy gloves but the reality is that it is physically impossible to remove vomit chunks from within and beneath the rear seat of a car. It would be easier to recreate Jurassic Park in your garden.
16.00 Receive text message to inform you that the insurance payments you think are going out monthly have not been and you now have 24 hours to sort out your direct debit or you are driving uninsured.
16.30 Eventually get through to the insurance company to sort out direct debit. Hastily put together a shameful dinner of chicken nuggets and chips, with some peas providing a veneer of healthy eating and good parenting. Read some Facebook posts and argue with someone on Twitter while you cook. Answer three work-related emails and make arrangements to work from home for two days while dealing with low-level guilt about the extra work this will mean for someone else and fear about the implications for your weekend workload.
17.00 Your TV subscription has apparently expired. The new bank card you had to order when the old one got lost (later found) has a different number and so none of your automated payments now work. At least that only takes 90 minutes to sort out.
18.30 Commence ‘bedtime’. Like breakfast in reverse but with the added frisson of very tired children and hungry cranky adults. Phone constantly buzzing in pocket with notifications from Instagram, Twitter, Facebook and WhatsApp. Realise halfway through the process that you still haven’t made two phone calls you’ve been meaning to make for a week.
20.00 Too tired to cook dinner, you get in a takeaway, the enjoyment of which is ruined by a combination of financial and health-related guilt. Eat food in front of TV while reading internet pages relating to the TV programme you are watching: ‘He was in The Good Wife! I knew it.’ Fight a nagging sense that you really aren’t following the plot line as closely as the writer probably intended.
23.30 Go to bed, already destined not to get close to eight hours’ sleep. Forget to turn off ‘notifications’ on phone.
2.00 a.m. Woken by a series of notifications relating to a conversation you aren’t a part of, which is being had by a group of people who are in the same bar as each other but in a different time zone from you.
Perhaps that typical day is slightly exaggerated, although in all honesty much of what I’ve outlined is semi-autobiographical and not too wide of the mark for many days I’ve had. It would be ridiculous though to suggest that our ancestors didn’t have some daily stresses that were more trivial than imminent death from a marauding predator or some natural disaster. The evolution of agriculture and the consolidation of populations into more concentrated urban centres would certainly have created and amplified a whole suite of potential stresses that begin to feel like ‘modern’ problems. Difficult relationships, family politics and social interactions are not recent inventions and would certainly have been exacerbated by centralised urban living. The ability to cope successfully with such potentially stressful social situations would certainly have been an advantage to our ancestors. Indeed, the evidence from primates shows that the ability to navigate social situations is a feature of some primate brains and arose long before the evolution of modern humans. Likewise, there is no reason to assume that what we might consider to be ‘modern’ feelings, like guilt, shame and anxiety (more of which shortly), or feeling the weight of others’ and your own expectations did not feature in the emotional palette of early humans and that these feelings were not enhanced or at least made more significant in our daily lives as we developed from a hunter-gatherer lifestyle into one more focused on city states, production and ‘civilisation’.
The signature of the modern world
What is so characteristic of the modern lifestyle for many of us is the presence of a daily series of almost continuous micro-stresses that have only come into existence very recently, arguably in some cases in the last five to ten years (for example, stress caused by social media or ‘phone addiction’). Physiological stress, as defined by the consequences of the hormonal and neuronal mechanisms we met earlier, evolved as a means to deal with situations that require ‘fight or flight’. A squirt of adrenaline and some raised blood pressure and heart rate is ideal if you lose your footing while out collecting berries or during the final stages of a hunt (these are after all potentially existential crises), but is clearly overkill in response to a ‘difficult’ email from your boss. Despite that, our basic biological set-up is largely unable to tell the difference and so, if we are prone to getting stressed, we can end up feeling stressed almost constantly. Technology has changed our environment far quicker than we can respond either socially (through established rules of engagement for example) or evolutionarily. The resulting mismatch between our physiology and the environment is great news for purveyors of relaxation courses and spa breaks, but it is bad news for our health.
The cumulative effects of chronic stress are well documented. Experiences of prolonged or recurrent stressful events in daily life, especially those which are seemingly (or actually) beyond our control, result in the activation of the stress response and the release of stress-related hormones. Producing these stress hormones in an active attempt to maintain homeostasis (and thereby prevent damage) in the body has been termed allostasis. The flip-side of this hormonal balance, the wear and tear that can be caused by prolonged periods of elevated levels of these hormones, has been called allostatic load. Our total allostatic load is the combined cumulative strain that chronic stress, exacerbated by a modern lifestyle, puts on various systems including cardiovascular, metabolism, immune, endocrine (hormonal) and nervous systems. Thus stress itself isn’t an illness but it can cause serious illness if it is allowed to continue. This is because the multi-system damage that is caused by the chronic presence of stress hormones makes us susceptible to health issues that include high blood pressure and subsequent heart damage, diabetes, rheumatoid arthritis, suppression of our immune system and mental health issues.
Stress and mental health
Decline in mental health marked by an increase in depression, anxiety and other disorders is undeniably one of the major medical trends in recent years.5 In the UK, the National Institute for Health and Care Excellence (NICE) lists as common mental health disorders depression, generalised anxiety disorder, social anxiety disorder, obsessive compulsive disorder and post-traumatic stress disorder (PTSD), and most of these show a sharp increase in the number and proportion of sufferers in recent years. For example, the proportion of people suffering from generalised anxiety disorder rose from 4.4 per cent in 2007 to 5.9 per cent by 2014, depression from 2.3 per cent to 3.3 per cent and OCD from 1.1 per cent to 1.3 per cent. Set against a UK population of around 65 million people, these disorders account for millions of people suffering from conditions that we know can be triggered by, and greatly exacerbated by, chronic stress.
Of course, apparent increases in certain disorders might be because of a greater recognition of those disorders, both by sufferers, who may be likely to seek help for symptoms that are linked to named and well-known disorders, and by medical professionals, who may be more likely to diagnose such disorders. The increase in prevalence of a disease or disorder because of an increased tendency to diagnose it might be expected to be especially great in mental health disorders in recent years. We have undergone something of a social epiphany lately in recognising the importance of mental health, and the public discourse on this topic is far more open and inclusive than it ever has been. That both Princes William and Harry, for example, feel able to speak openly of their emotions and feelings triggered by the death of their mother, and are able to place those experiences within the framework of mental health, shows how far we have come in recognising that the pressures and stresses of the lives we lead can cause serious problems. A similar background of celebrity-led awareness of mental health issues has been seen elsewhere with Ariana Grande, Justin Bieber and Lady Gaga all opening up publicly in the USA about mental health pressures.
The social background of increased awareness and openness about mental health issues is a problem when it comes to interpreting trends. It is possible though to begin to tease out the different factors that might account for a rise by comparing different sectors of the population in carefully planned and conducted studies. An examination of the prevalence of depression in the USA and its possible link to substance abuse, for example, concluded that depression had more than doubled in the 10 years between 1992 and 2002, increasing from 3.3 per cent to 7.1 per cent. Their structured approach allowed them to show that there were significant increases across age ranges and the increases were irrespective of whether people were white, black or Hispanic. Their initial hypothesis, that depression increases could be linked to substance abuse, was only supported for black men aged between 18 and 29, but they did acknowledge that increased awareness of depression via media campaigns and the advertising of antidepressants may have played a role in the overall increase in prevalence. As they point out, ‘These campaigns began during the interval between the two surveys, and just such a general factor is consistent with the broad-based increases seen in this study.’ That point notwithstanding, their overall conclusion was still that depression had increased in prevalence and that this increase, if it continues, is likely to have profound effects on public health and on the economics of healthcare. Their overall conclusions are echoed by a great many studies on the epidemiology of depression and anxiety disorders; these disorders are increasing, and this is a problem. What is more, there seems to be good general agreement both in the scientific literature and in the webpages of reputable health advisory bodies like the NHS in the UK and the Mayo Clinic in the USA, that lifestyle stresses are a significant contributory factor.
That many authorities reach the same conclusions, both on the rise of mental health issues and the cause for that rise, still doesn’t remove the possibility that we are seeing the influence of an increased tendency to seek help for, and be diagnosed with, disorders like depression and anxiety. A tendency to rush into a diagnosis of ‘depression’ for what might otherwise be termed ‘normal feelings of sadness’ was explored in the book The Loss of Sadness: How Psychiatry Transformed Normal Sorrow into Depressive Disorder by Allan Horwitz and Jerome Wakefield.6 In it, they discuss the idea that the boundaries of depression, and thereby the diagnostic criteria that are used to diagnose it, have broadened considerably since 1980 when the American Psychiatric Association’s hugely influential Diagnostic and Statistical Manual changed from classifying mental health disorders based on potential causes to an approach based on symptoms. Horwitz and Wakefield argue that this resulted in a far more inclusive definition of depression that brought ‘normal sadness’ and short-lived unhappiness, which might be rightfully regarded as part of the normal human experience, into the fold of clinical depression. While this may well account for some of the increases in depression (and other disorders) observed around the world, the link between modern lifestyle, stress and subsequently impaired mental health is widely supported and it has become an important part of our understanding of mental health in recent years.7
The evolution of emotion
Understanding that stress can be a causal factor in mental health is one thing, but to piece together the evidence that this is somehow caused by an evolutionary mismatch requires us to put together an evolutionary argument. It is entirely appropriate that Charles Darwin can provide us with the beginnings of just such an argument. Darwin was the first to suggest that human emotions, and in particular the facial expressions associated with emotions, were evolved traits that adapted over time in response to selection. As is so often the case with Darwin, subsequent research has largely confirmed his thinking. We have already seen the importance of the developing agricultural environment in shaping our recent physical and physiological evolution when it comes to nutrition, and there is no reason to assume that it didn’t also play a role in shaping our stress responses, both physiologically and psychologically. One emerging theory on the evolution of guilt, shame and anxiety (more and more associated with the stress of a modern lifestyle) is that these emotions evolved as a response to the combination of cooperation and aggression that allowed us to become so dominant globally (more on the role of violence in our past and present lives in Chapter 7). The theory, advanced by Peter Breggin, supposes that the potent combination in our early evolution of close-knit social groups and a tendency for violence would make it extremely difficult to live together without destroying each other.8 The solution was the evolution of emotional restraints against ‘aggressive self-assertion within the family and other close relationships’. Thus guilt, anxiety and shame may have evolved as mechanisms to counter our violent tendencies. While undeniably useful, evolved emotional restraints against violence have now become constraints, with guilt, shame and especially anxiety becoming socially and emotionally crippling in the modern world. In many cases, the trigger for anxiety is stress, often chronic but also acute. Anxiety in particular has created a veritable ecosystem of different recognised disorders including generalised anxiety disorder, panic disorder, obsessive compulsive disorder (OCD) and post-traumatic stress disorder (PTSD).9
The link with stress is apparent quite clearly in the name of PTSD, but it is important to emphasise that not all anxiety (and not all depression for that matter) is a consequence of the sort of stress our modern lifestyle places on us. There are a wealth of reasons why a person might develop an anxiety disorder, and we are still at the start of understanding the complexities of depression, its causes (which, as discussed in Chapter 4, may even be associated with our gut bacteria) and its treatment. Nonetheless, we do know that chronic stress causes elevated levels of cortisol, the ‘stress hormone’, and reduced serotonin. Serotonin is sometimes called the ‘happy chemical’ and although it is closely linked to mood and anxiety, it also has a series of complex roles in aspects of our biology that are themselves linked to our mood, including appetite, eating behaviour and sexual behaviour. Thus, we can certainly make some very solid links between the biochemical products of stress and symptoms related to anxiety and depression, but we are still pinning down the precise connections.
Other brain-related problems that are increasingly linked to stress are Alzheimer’s disease and dementia. Studies of mice have shown that provoking modern life-like emotional and physical stresses on mice severely impaired memory and may exacerbate the sort of cognitive defects found in the very early stages of Alzheimer’s. If mice aren’t convincing enough for you (and as useful as they are in biomedical science, they shouldn’t be that convincing), a major review of the literature on stress and dementia risk in humans concluded that stress could indeed play a role in the risk of dementia but that it is part of an array of risk factors. It is not surprising perhaps that stress might play a part, since we know that the immune system takes an important role in the development of dementia, and we know that stress hormones affect the immune system. It is also not surprising that disentangling the connection between lifelong chronic stress and later-life dementia is far from straightforward, and it is very hard practically to investigate a lifetime of stress in any sort of robust scientific manner. However, studies are under way and given the increasing focus on dementia generally, and Alzheimer’s in particular, it seems likely that we will uncover both the scale of the risk and the underlying mechanisms in the near future.
Another health implication of stress that is understandably concerning is the potential link with cancer. However good such a connection may be for headlines though, the science is not supportive. Cancer Research UK is candid in its appraisal of the evidence, stating plainly and unambiguously that ‘Most scientific studies have found that stress does not increase the risk of cancer.’10 Others have been plainer still, dismissing fears that stress causes cancer as a ‘myth’.11 While some small-scale studies have suggested links, for example with breast and gastrointestinal cancer, larger long-term studies and meta-analyses of multiple studies have consistently found no link between stress and the four most common cancers in the United Kingdom (bowel, lung, breast and prostate). Behaviours associated with stress, like drinking alcohol and smoking, poor diet and a lack of exercise (which may also help to promote stress) can and do lead to cancer, but in this case the connection with stress is indirect. The current lack of evidence for a direct link is in one sense reassuring but, if we consider what we already know about the mechanism of stress and the multiple systems that stress affects, it is also surprising. Long-term release of stress hormones can induce DNA damage and affect DNA repair as well as weaken and dysregulate the immune system, all of which are implicated in the development and progression of cancer. It does not then seem unreasonable to suggest such a link could exist and while we don’t yet have convincing evidence, I am certain that we will see much more research into the connection between stress and cancer (most likely mediated through our immune system) in the coming years. My money would be on Cancer Research UK having to change its website text at some point in the future, but for now we have to say that the evidence is lacking.
Further complicating the issue of chronic stress and our understanding of its effects is the fact that the accrual of damage across multiple systems that is caused by chronic stress increases as we age but actually plateaus at around 60. This sets up a situation whereby the damage caused by stress in early life is only manifested in much later life. Of course, from an evolutionary perspective this is not necessarily good news for our youthful well-being in the long-term. This is because negative consequences of behaviour that only occur after we have reproduced are more or less invisible to selection. However, although Alzheimer’s and heart disease brought on by chronic stress might only manifest in later life, there are many other symptoms of chronic stress that manifest far earlier and certainly do have a profoundly negative impact on our quality of life and, by inference, our reproduction. If you had a genetic tendency to be able to handle modern-life stress then some of the early manifested side effects, like a reduced sex drive, depression and insomnia, which would arguably reduce your ability to reproduce, would be avoided. Assuming that the all-important genetic basis for ‘stress immunity’ is present (without which evolution cannot proceed), then it is possible that if stress has a sufficiently large negative influence during our peak reproductive years we might see selection for physiologies that are better able to handle stress. Evidence suggests that this may well have already occurred.
We have seen that acute stress can exacerbate or trigger underlying conditions such as heart disease (as seen in the Athens earthquake study) that we know have a genetic component. However, there may be a more direct genetic link with our ability to handle, or not handle, stress. One key gene implicated in this link is the gene that codes for an enzyme called catechol-O-methyltransferase, known more conveniently as COMT. COMT catalyses the breakdown of catecholamines, a category of neurotransmitters. We have met catecholamines several times already because this family of compounds includes adrenaline and noradrenaline as well as dopamine. It is dopamine in the brain that is the primary target for COMT. The gene coding for COMT has a naturally occurring variant in its genetic code. The variant, when it is translated by our cellular machinery and used to assemble the COMT enzyme, substitutes the amino acid valine that should be in position 158 for methionine. Not such a big deal you might think, and in some cases the odd amino acid substitution in the chain of amino acids that make up a protein makes little difference to the functioning of that protein. In the case of the 158 substitution in COMT, the different properties of valine and methionine and the subsequent differences these amino acids confer on to the final enzyme make a very big difference. The valine version of COMT is more than four times more effective than the methionine version in breaking down dopamine.12
COMT is used preferentially in the prefrontal cortex of the brain, accounting for 60 per cent of dopamine breakdown occurring there.13 Located right at the front of the brain, the prefrontal cortex is involved with complex thought, planning, decision-making, moderating social behaviour and key aspects of personality. It is here that the different COMT variants show their effects. Under conditions where dopamine release may be high (for example stressful situations), individuals with the valine variant perform better and feel less pain. This variant may be particularly useful in threatening environments where peak performance is an advantage despite stressors like the imminent threat of death or pain. As a consequence, this variant has become known as the ‘warrior’ genotype. In contrast, the methionine version allows bearers to perform better in memory and attention tasks, making these people thinkers rather than fighters. Perhaps because of the pleasing rhyme and alliteration this variant has become known as the ‘worrier’ genotype.12 ‘Fighter’ and ‘thinker’ feel like less pejorative titles but ‘worrier’ links nicely to the idea that increased stress leads to anxiety and to further issues. The ‘worrier’ genotype seems to have evolved more recently. Its evolution is suggested to reflect selection in more complex environments where maximal performance on complex attentional and memory tasks may have been more important for survival and reproduction than a more straightforward ‘hit it and run’ strategy. The persistence of both variants (an example of a polymorphism) is likely a reflection that both forms have a selective advantage depending on the environmental circumstances; sometimes it is better to be a warrior and sometimes it is better to be a worrier.
The drip-drip of modern stress might seem to favour the warrior genotype in terms of the health benefits of dealing with stress, but the complexities of modern life favour the worrier. Balancing the worrier-warrior seesaw feels like a uniquely human problem and indeed until recently it was thought that the COMT 158 polymorphism was only found in humans. Recent research though has revealed that the polymorphism exists in other primates.13 Assam macaques are monkeys that live in large groups with plenty of aggressive social interactions. Studies of their aggression, dominance hierarchies and genetics showed interesting and complex links between which variants of the COMT gene individuals possess and how they express aggression when they are dominant. It isn’t quite as simple as ‘warrior’ versus ‘worrier’ in macaques, and studies that link COMT to wider characteristics of aggression in humans have found much the same complexity. Differences in susceptibility to certain behaviours and conditions link with ongoing environmental conditions, past environments and genotype to create complex relationships between factors that are not always easy to disentangle from each other. The discovery of a primate with the same polymorphism and similar links to aggression and social stress provides a potential system to disentangle those connections in a much more controlled and experimental way than is currently possible with humans. Of course, the ethical dimensions of such studies are far from straightforward.
Can we ‘heal’ stress?
If long-term modern-world stress is bad and inherently biochemical in nature, then can we not simply block the biochemical pathways that result in, for example, the production of cortisol? The problem with such a direct approach, as tempting as it sounds, is that our hormonal system is so complex and interconnected that such an intervention would have a range of unwanted effects. Some indication of this is provided by the suite of symptoms associated with cortisol deficiency, which can occur if the adrenal glands stop functioning correctly (a deficiency known as Addison’s disease) or if the pituitary gland is unable to produce the hormones that tell the adrenal glands to produce cortisol. Although cortisol is one of the main mediators between chronic stress and disease, an inability to produce it does not result in better health; far from it. Cortisol deficiency results in fatigue, dizziness, weight loss, muscle loss and mood changes and without treatment in the form of cortisol supplementation it can be life-threatening.
The complexity of our endocrine system and its association (or not) with stress-related conditions does not lend itself to simple ‘turn it off’ interventions and, as might be expected, the general treatment advice for patients suffering from stress is not straightforward. The NHS in the UK takes a hands-on, problem-solving approach, which I think may be less than helpful if you are stressed. Heading up his ‘10 Stress Busting Suggestions’, Professor Cary Cooper, an occupational health expert from the University of Lancaster, is quoted as saying ‘In life, there’s always a solution to a problem. Not taking control of the situation and doing nothing will only make your problems worse.’ In other words, get a grip and sort out your problems; pull yourself together! I don’t disagree with the sentiment, but it also feels a little like shouting to someone dangling off a cliff edge to ‘hang on!’ It is undoubtedly very good advice, but not especially helpful in the situation. Likewise the top 10 stress busters all sound excellent (‘take control’, ‘help other people’, ‘try to be positive’, ‘work smarter not harder’, ‘be active’ and so on) but in reality may be difficult to manage if you are gripped by anxiety and unable to do anything, let alone ‘connect with people’ or ‘challenge yourself’. Other advice on the site includes some breathing exercises, time-management techniques and a recommendation to ‘take a holiday’. Having seen some people in the grips of an anxiety episode, advising them to book a holiday seems about as useful as suggesting they ‘plan the next Moon mission’ in terms of its achievability, at least in the near future. Overall, the advice from a range of sources is neatly summed up by ‘It’s important to tackle the causes of stress in your life if you can. Avoiding problems rather than facing them can make things worse. But it’s not always possible to change a stressful situation. You may need to accept there’s nothing you can do about it and refocus your energies elsewhere.’ Easier said than done for many, I would suggest.
There is ample evidence to say that our current way of life is bad for our health in a multitude of ways and that the stresses associated with life only seem to be getting worse. Despite the difficulties in disentangling the various different factors that contribute to any particular disease, the links between stress and that disease, and perhaps hardest of all, the different factors that contribute to stress, there is little out there to suggest that stress is getting better. This has likely been the case for some time now, possibly even millennia. The usual pattern is to view human history as a series of great accomplishments, each of which led to longer, safer, more productive lives and a greater measure of what we have come to recognise as ‘civilisation’. Thus, we look back at the rise of the modern human through the lens of technological aggrandisement; the Stone Age; the Bronze Age; the Iron Age; the development of agriculture; the industrial revolution; the rise of medicine; the internet and so on. I would argue that, perhaps with the exception of medicine, the same history could be viewed as an ever-increasing opportunity to introduce more stress into our lives. ‘Keeping up with the Jones’s’ probably started the second that we had neighbours and something meaningful to compare with them. I can see no reason to think that early flint knappers for example, pioneers at the very start of our technological progress, didn’t experience some sort of stress and anxiety when comparing their efforts with others. Likewise, the ability to accrue ‘wealth’ in whatever form would lead to stress, whether it be from a modern job or from being an early, successful farmer supplying the local city-state with produce. Where truly modern life excels though, is in the range of potential stresses, their pervasiveness and our inability to shut them down. Modern life is an equal-opportunities stress provider and few seem to escape its ravages in one way or another. Dealing with stress is clearly important but when the best advice available boils down to ‘try to refocus your energies’, it is clear we are quite a way behind the curve in dealing with the problem medically and socially.
Perhaps the most pivotal technological development in the development of human stress is the rise of the internet, together with the associated rise in mobile technology and resultant ‘always on’ culture. The evolution of a sharp intellect and well-tuned social skills dramatically intersect with the sudden global rise of the internet in ways that produce some of the most spectacular and damaging mismatches between our evolutionary legacy and the modern world. It is to this uniquely twenty-first-century problem that we now turn our attention.