Cortisol: more than just a stress hormone

Cortisol is often simply referred to as the stress hormone, but its function is much more wide ranging than that. It's linked to general health and wellbeing while dysfunction is thought to impair memory, contribute to depression and play a role in burnout. In healthy people, cortisol also follows a pretty regular daily routine, predictably rising and falling at certain times and after certain activities (such as eating and exercising). It's therefore vital to maintaining the human circadian rhythm, or 24-hour (or thereabouts) biological cycle that includes everything from sleeping and waking to blood pressure and body temperature. It's therefore easy to see how chronic stress can cause all sorts of problems.

The Cortisol Awaking Response (CAR)

When we wake, our cortisol levels increase significantly and rapidly. Indeed, there is a 50 per cent increase in cortisol levels within 20 to 30 minutes of us waking up. So important is this process that it even has a name: the Cortisol Awaking Response (CAR). Just like cortisol generally, the awaking response is vital for health and wellbeing, with an abnormal response being linked to type 2 diabetes, chronic fatigue syndrome, multiple sclerosis, burnout, amnesia, depression, eating disorders and PTSD. Functioning of the CAR has also been found to predict overall health and survival from cancer.

Psychophysiologist Angela Clow of the University of Westminster has discovered other links between CAR and stress, sleeping patterns, shift work and pain (Clow, Hucklebridge, Stalder, Evans & Thorn, 2010). In addition, Clow has found that our waking cortisol response is healthier when we rise early, are exposed to daylight, have regular routines and exercise. Mark Wetherell of the University of Northumbria found that a bigger morning peak in cortisol levels occurs when we have an exciting or demanding day ahead. Even more interesting, perhaps, Wetherell also found that these levels don't fall even when the planned event doesn't take place (Wetherell, Montgomery & Smith, 2015).

Cortisol is, therefore, important to our physical and psychological health and receiving that early morning boost can certainly make the day appear a little brighter. You might then assume that keeping these levels high is advantageous in some way, not least because we are kept in a state of anticipation and alertness. But prolonged elevated levels of cortisol is not a particularly good situation to find ourselves in for many reasons. One is that cortisol is involved in the control of our immune system and prolonged high levels can lower our ability to fight off infection, making us more susceptible to illness and other health problems, including diabetes, weight gain, cardiovascular disease and lowered fertility levels. Vivette Glover, professor of perinatal psychobiology at Imperial College London, found that mothers who were stressed during pregnancy were more likely to have children with emotional problems, ADD and delayed cognitive development (Glover, 2014). Of course, a number of other factors were also involved but Glover did discover a specific measurable effect of cortisol.

Stress can, therefore, have a devastating impact on the human brain and body. But the brains of young children are still developing, sometimes in the most curious ways. As a result, young people are at greater risk from higher levels of stress, so much so that we can actually identify the damage that stress has on the developing brain and cognitive function. Children who have experienced prolonged periods of stress score lower on tests of spatial working memory than their less stressed peers; they also have problems completing other short-term memory tests (Hanson et al., 2012). Some of these issues might relate to the impact anxiety has on the completion of such tests, but these young people also display physical brain abnormalities. Of course, we are talking here of extreme levels of on-going stress, rather than the daily stressors experienced by all individuals. But apart from helping us to escape that wild animal, are there any other positive benefits of being in stressful situations?

The positive side of stress

Back in 1908, psychologists Robert Yerkes and John Dillingham Dodson (Yerkes and Dodson, 1908) discovered that animals performed better on tasks when they were made moderately anxious beforehand. However, task performance became impaired when the animals experienced very high levels of anxiety. This concept is now referred to as the Yerkes-Dodson law. But the ability to deal with anxiety differs from person to person and is the result of both genetic predispositions and environmental factors. Of course, it's not just about anxiety but it is about arousal.

Arousal is a biological state that some people crave more than others. The adrenaline junkie craves stimulation, happy when ascending a rock face or hurtling to the ground with only a bungee separating life from death. The thrill seeker will get bored easily and needs to move on to something more exciting to that which previously stimulated. Others don't require such high levels of stimulation, our brains are aroused enough by the simpler things in life. We all, therefore, have significant differences in the optimal level of arousal; the thrill seeker feels happiest at the extreme end of the scale (his or her optimum level), a level that would cause high levels of damaging anxiety in people who require much lower levels of arousal. However, that doesn't mean that they don't experience fear (see Chapter 9).

The Yerkes-Dodson law seems intuitive, but might not live up to the hype (see, for example, Teigen, 1994). Arousal does make a difference, whether it be our desire to excite or inhibit it, but whether we can describe it as an all- encompassing law is a topic of debate (although not very heated). Generally, however, stimulate us and we move towards optimal functioning, push us over the optimum and we suffer, yet only we can know where that optimal level resides and even then, our judgments can often be way off.

Anxiety is, therefore, partly concerned with being pushed over our individual threshold, but it's also about what has come before. Anxiety is cumulative, in that seemingly innocuous daily hassles can build up until we reach that destructive final straw (as was discussed in Chapter 3).

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