Stress not only kills brain cells, stress kills people.
We learned that stress is a killer from an important study on civil servants carried out in the UK more than half a century ago. In this study, Michael Gideon Marmot, then with the University College London, and his colleagues designed the first of two studies that become known as the Whitehall Studies.
The original study started in 1967, following 18,000 male civil servants over 10 years. The results, confirmed in a second study in 1985, show a strong association between job grade levels of civil servant employment and mortality rates from a range of causes.
The number of men in the lowest grade (messengers, doorkeepers, etc.) who died was three times higher than that of men in the highest grade (administrators). Still, despite this association – that stressful jobs kill people – the mechanism of how stress causes lethal disease remained elusive.
Then in 2017, a new study highlighted some of the mechanisms involved. Ahmed Tawakol with Massachusetts General Hospital and Harvard Medical School and his colleagues followed 293 patients for just under four years.
During this time, 22 patients developed heart disease. The researchers found that excited brain activity – in a region called the amygdala – proved to result in heart disease. The authors suggest that this brain area signals to the bone marrow to produce extra white blood cells, which contributes to arteries developing plaques and become inflamed, which then can cause heart attack and stroke.
The brain, by protecting the body – building up defences against stress – is causing the damage.
Like a tree that does not get watered, the brain withers. With a withered brain you are more likely to experience dementia if the few remaining neurons are infected or damaged
Although we have no information on severe trauma from Malta, other than work stress, we do have data from the United States. In 2000 Ronald Kessler with Harvard Medical School reported that at least half of the US population had some kind of trauma in their life. One in five cases, the trauma is severe enough to result in posttraumatic stress disorder (PTSD).
PTSD is twice as common in women as in men, and affects just under one out of 10 Americans. For women, childhood sexual abuse is the most common trauma, while for men physical assault remains the most common form of trauma. There is a long history of studies showing that traumatic stress leads to a range of mental disorders, including PTSD, depression, alcoholism, dissociation, anxiety and borderline personality disorder. But does it contribute to dementia? The evidence is unclear.
We know that severe stress caused parts of the brain (hippocampus) directly involved in memory to shrink by eight per cent. Douglas Bremner wrote an excellent review of how stress shrinks the brain in 2012. And we have other historical evidence as well, where severe stress affects memory.
Danish survivors of World War II concentration camps complained of memory problems, as did American prisoners of war from the Korean War. Anyone who has been through a death of a loved one, a divorce or a sudden negative experience (health, jail, or money problems) can testify that you start to forget. Although some stress-related memory loss is temporary, the problem is that continued stress causes long-term problems. When we look at the history of someone’s stressful situations, then the picture changes.
Being traumatised as a child has long-lasting effects. Having a history of trauma in childhood makes you more likely (by four times as much) to get PTSD when exposed to a trauma as an adult. The implications are that early abuse may limit the capacity to grow new neurons in the brain, which leads to having less opportunity to deal with stress at later life.
Studies with rats show how stress reduces the growth of neurons and its branches. Like a tree that does not get watered, the brain withers. With a withered brain you are more likely to experience dementia if the few remaining neurons are infected or damaged. We can see how stress can cause dementia, but not all dementia is caused by stress.
The question as to why does the brain respond this way to trauma requires some speculation. Looking at the mechanics of how the damage is done does not explain the ‘why’. Perhaps the damage is random, a mistake. But the body is more complex and sophisticated than that.
Perhaps the brain, sensing that we are hurt, tries to diminish the sensory experience. If it cannot run away from the stress, or eliminate the cause of the hurt, then it can reduce the impact. The brain seems to be reducing how much we feel the pain.
By reducing neurons and limiting the strength of their signal, perhaps it’s the brain’s attempt at lowering pain. Sometimes the best intentions end up with unforeseen and long-term consequences in older age. Stress is definitely something to address from an early age.
Mario Garrett was born in Malta and is currently a professor of gerontology at San Diego State University in California, US.