Stress pervades our lives. We become anxious when we hear of violence, chaos or discord. And, in our relatively secure world, the pace of life and its demands often lead us to feel that there is too much to do in too little time. This disrupts our natural biological rhythms and encourages unhealthy behaviours, such as eating too much of the wrong things, neglecting exercise and missing out on sleep.
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The psychologist Jerome Kagan at Harvard University recently complained that the word ‘stress’ has been used in so many ways as to be almost meaningless; he suggests it’s warranted only for the most extreme circumstances or damaging events. But my decades of experience suggest another approach. The insidious power of stress to ‘get under the skin’ was the focus of a MacArthur Foundation Research Network that I joined more than two decades ago, uniting me with social scientists, physicians and epidemiologists around a common problem: how to measure and evaluate stress from our social and physical environments. Our collaboration, continued under the auspices of the National Scientific Council on the Developing Child, has shown that stress acts on the body and brain, profoundly influencing health and disease.
Our findings are nuanced, starting with the fact that not all stress is the same. ‘Good stress’ involves taking a chance on something one wants, like interviewing for a job or school, or giving a talk before strangers, and feeling rewarded when successful. ‘Tolerable stress’ means that something bad happens, like losing a job or a loved one, but we have the personal resources and support systems to weather the storm. ‘Toxic stress’ is what Kagan refers to – something so bad that we don’t have the personal resources or support systems to navigate it, something that could plunge us into mental or physical ill health and throw us for a loop.
Now let us put these three forms of stress into a biological and behavioural context by invoking ‘homeostasis’ – the physiological state maintained by the body to keep us alive. It is through homeostasis that we maintain body temperature and pH (alkalinity and acidity) within a narrow range, keep our tissues perfused with oxygen and our cells fed. To maintain this steady state, our body secretes hormones such as adrenalin. Indeed, when we encounter an acute perceived threat – a large, menacing dog, for example – the hypothalamus, at the base of our brain, sets off an alarm system in our body, sending chemical signals to the pituitary gland. The pituitary, in turn, releases ACTH (Adrenocorticotropic hormone) that activates our adrenal glands, next to our kidneys, to release adrenalin and the primary stress hormone, cortisol. Adrenalin increases heart rate, blood pressure and energy supplies; cortisol increases glucose in the blood stream and has many beneficial effects on the immune system and brain, among other organs. In a fight-or-flight situation cortisol moderates immune-system responses, and suppresses the digestive system, the reproductive system and growth processes, as well as signalling brain regions that control cognitive function, mood, motivation and fear.
Biochemical mediators such as cortisol and adrenalin help us to adapt – as long as they are turned on in a balanced way when we need them, and then turned off again when the challenge is over. When that does not happen, these ‘hormones of stress’ can cause unhealthy changes in brain and body – for example, high or low blood pressure, or an accumulation of belly fat. When wear and tear on the body results from imbalance of the ‘mediators’, we use the term ‘allostatic load’. When wear and tear is strongest, we call it allostatic overload, and this is what occurs in toxic stress.
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Failure to turn on cortisol when needed is bad, leaving the door open for the body’s inflammatory response to compensate in an imperfect way. Too much inflammation can kill us as in septic shock. Failure to turn off cortisol after the stress is over produces negative effects too. Among the consequences are an increase of fat production, leading to obesity, diabetes, depression and eventual heart disease – all contributors to allostatic load.
Given our need for a robust cortisol response in the face of stress, the second misunderstanding about cortisol is the notion that it’s the ‘bad guy’. Rather, cortisol has a normal physiological role; it helps us adapt to stressors and coordinates our metabolism with daily activity and sleep patterns. We would not live very long or well without our cortisol! As my former student Firdaus Dhabhar, now a neuroimmunologist at the University of Miami, found, the early morning rise of cortisol, along with the stress response, activates immune function so that we can fight an infection or repair a wound. Likewise, the normal ‘morning awakening’ rise of cortisol that helps rouse us and makes us hungry for breakfast enhances the body’s response to immunisation if administered in the morning. The body’s response is like an orchestra involving many players working in harmony.
PG notes the holiday season can be an occasion for heightened stress.