Many of us have felt the damage stress can cause; but connecting the dots between chronic stress and disease is more difficult than you’d think.
This network of hormonal pullies and brain-based levers helped your forebears roaming the African savannah evade predators and stave off infection. But these days your stress response can be more enemy than ally.
Much of our stress response machinery is designed to respond to short-term, or acute stress. So swerving your bike away from a careering car, or knuckling down to meet a work deadline are the modern equivalents of leaping away from a lion’s swipe. Once the danger has been averted, your body sets about calming things down again.
But when an event or situation – otherwise called a stressor – lasts for months or even years, chronic stress is the result. Caring for a loved one with cancer, being under financial pressure, or not having significant social contact with others can all lead to chronic psychological stress.
But determining how much chronic stress impacts on your health is challenging, as every one of us responds differently to potentially stressful situations.
“Stress is when the demands of your environment exceed the coping resources that you believe that you have,” says Dr Mary-Frances O’Connor, psychologist and stress researcher at the University of Arizona. “So in all cases, there’s perception – perception of what the environment demands and perception of your own ability to cope with it.”
“Part of why stress research is difficult is that when you’re talking about human beings, there’s a subjective component,” says O’Connor. Even in bereavement, an area O’Connor has researched extensively, individuals have varied responses to the death of a loved one.
With no stressor able to be objectively classified as always stressful to all people, researchers must rely on personal accounts of feelings and experiences, and try to match them up with physical changes that occur.
Despite the challenges, clear patterns are emerging in how chronic stress affects our biology, and our health.
The cortisol connection
When you spring into action in response to an acute, fight-or-flight situation, your body prioritises a heightened sense of perception and increased blood flow to our muscles, over less critical functions like digestion and reproduction.
These rapid changes are primarily at the behest of the stress hormones cortisol and adrenalin, which are released from the adrenal glands in response to messages sent from your brain. While cortisol rallies energy, adrenalin works on nerve cells to increase blood pressure and heart rate and sharpen our senses.
“Cortisol’s job is to give you that energy in the right place at the right moment,” says O’Connor.
Cortisol is essential for highly charged situations, but also plays a role in the minor ebbs and flows of everyday stress. When you wake up in the morning, a spike of cortisol rallies your resources, helping you get up and face the day ahead.
“Even emotionally, what we are preparing for matters,” says O’Connor. “Peoples’ cortisol spike in the morning is higher on a work day than on a weekend.”
With chronic stress your cortisol response is tempered. The relentless buzz of stress in the background flattens out the daily highs and lows of cortisol.
“You’re both not mounting as good a response, and you’re also not relaxing as much as you could at the end of the day, and both are bad,” says O’Connor.
Chronic stress and the immune system
Cells throughout your body – including immune cells that fight illness – respond to cortisol’s call. When you are chronically stressed, these cells become weary of the constant bleating of the alarm signal and start ignoring its presence. The cortisol resistance that develops may make you more susceptible to infections when chronically stressed.
Cortisol “tends to damp down levels of inflammation,” says Dr Erica Sloan, a cancer biologist at Monash University. Cortisol’s anti-inflammatory properties usually help to lessen the impact of a cold or flu by tempering the immune system’s response to infection.
Researchers at Carnegie Mellon University in Pittsburgh, Pennsylvania, conducted a study in 2012 that found people who had recently been through a stressful period were more likely to show signs of cortisol resistance. When deliberately exposed to cold viruses these people were also more likely to develop colds, and those who were more resistant to cortisol had higher levels of immune messengers that promoted inflammation, which made their symptoms worse.
“Inflammation in the short term can be really good and it’s a normal part of our immune response to infection or to wounding that allows the wound to heal,” explains Sloan. “The problem comes when the inflammation is not controlled and it’s not resolved within a certain time.”
Chronic inflammation occurs when inflammatory signals remain switched on for weeks or months on end. This type of inflammation has been implicated in a number of serious diseases including cardiovascular disease, cancer, diabetes, arthritis, Alzheimer’s disease, and autoimmune disorders. Even depression has been described as an inflammatory illness for some people, and antidepressants that decrease inflammation alleviate symptoms.
Chronic stress and disease
Chronic stress has been indirectly linked to greater risks of developing depression, cardiovascular disease, diabetes, autoimmune diseases, upper respiratory infections, and poorer wound healing.
While a direct link between chronic stress and disease is yet to be confirmed, it’s known to accelerate the pace of disease for those already diagnosed.
In a mouse study, Sloan found that while growth of a primary breast cancer tumour was unaffected by stress, metastasis (spreading of the tumour to new locations in the body) increased 30-fold. Metastasis is an indicator of poorer survival for women with breast cancer. Another mouse model of leukaemia also found chronic stress hastened cancer progression.
People with HIV have also been found to progress faster to AIDS when chronically stressed.
According to O’Connor, longitudinal studies that recruit people prior to any chronic stress or illness will be crucial to making the link between the two. In one such study, known as the Whitehall study, thousands of British civil servants were recruited and their health outcomes have been tracked over many years.
One analysis of Whitehall study data found that people who had encountered the stress of poverty in early life were twice as likely to develop cardiovascular disease as adults, irrespective of whether they had been able to work their way out of poverty.
Another Whitehall study found being in a job with low job control contributes to the development of heart disease in both men and women, a connection further bolstered by a recent study showing people who report feeling stressed are twice as likely to suffer a heart attack.
Protecting ourselves from chronic stress
While stress researchers continue to pick apart the connections between chronic stress and disease, others focus on ways to alleviate stress. Many stress reduction techniques also prevent a range of diseases.
Exercise, for example, helps to prevent a raft of life-threatening conditions such as heart disease, obesity, type 2 diabetes, high blood pressure and cancer, and can also play a role in keeping mental health in check by preventing depression and anxiety.
Unfortunately, as Sloan notes, “the first thing to go out the window when you’re stressed is looking after yourself, eating right, exercising”.
But better understanding the mechanics of stress in the body, we might be able to avoid paying for periods of stress after they’ve passed.
This article first appeared on the ABC Health & Wellbeing on 5 September, 2013.