Stress is bad for our physical and mental health. It has been linked to several leading causes of death, including heart disease and mood disorders, such as depression.

Now new research suggests that the actual number of stressful experiences we encounter can have dramatic consequences for the health of our brains.

In all, 27 events were identified as being particularly detrimental. These include being expelled from school during adolescence and experiencing unemployment as an adult.

Each instance of stress was said to age the brain by an average of 1.5 years. So exposure to a handful could set you back a decade in terms of cognition.

The research identifying the 27 events was presented at the Alzheimer’s Association International Conference in London in July 2017. A group from the School of Medicine and Public Health at the University of Wisconsin-Madison asked 1,320 people to remember the stressful events that had occurred across their lifespans and then complete a number of tasks to assess their thinking skills. These included tests related to various aspects of memory – known to deteriorate with age – such as the ability to accurately recall details from a story.

Participants who had experienced a greater number of stressful events were found to score poorly at these tasks, indicating a loss of cognitive function.

Linking these findings to dementia could undoubtedly help identify those most susceptible to developing neurodegenerative conditions – and lead to potential risk reducing interventions, designed to modify the effects of stress.

But is the onset of something as complex as Alzheimer’s disease likely to come down to a simple numbers game, in which one too many stressful events mean it’s game over?

Stress and the ageing brain

Reductions in the efficiency of our memory and thinking skills are a natural part of ageing. As the years pass, we lose brain tissue and cannot support cognitive functions as readily as in our youth.

But exposure to stressful episodes could feasibly speed up this process, producing accelerated or more pronounced decline. Those who took part in the study were on average only 58 years of age, yet there was already noticeable variation in their cognition on the basis of different stress levels.

While anxiety, depression and poor cerebrovascular health have been identified as potential risk factors for dementia, declines in cognition can occur for a variety of reasons.

Prolonged exposure to stress, which would be expected from the loss of a parent or having a child involved in a serious accident, leads to long-term alterations in the body’s response to adverse events – involving the hormone cortisol.

Chronic over-production of cortisol has a negative effect on regulatory systems responsible for mood, blood pressure, and immune system function. It also inhibits memory formation and learning in key brain regions such as the hippocampus, which is particularly affected in Alzheimer’s.

Mediating factors

There is likely a complex interaction between biological factors and our experiences, encompassing not only stress but also how mentally active we are, our nutrition, and exercise habits.

Lifestyle factors may provide a buffer against resulting brain damage, and support how the brain adapts to the challenge of ageing. This concept, known as “cognitive reserve”, explains why some people are more or less susceptible to the effects of stress.

Cognitive reserve defines brain function as something we have some control over – to shape our life course and maintain our thinking skills. This is surely welcome news in a world where exposure to stress seems unavoidable.

On the other hand, those less able to adopt positive choices appear to be the hardest hit. The researchers who highlighted the 27 events also found that the effects of stress were more profound in the African American population, who experienced 60% more stressful life events than their Caucasian counterparts.

With each life event adding years to their cognitive ability, this highlights the need for support in managing the potentially devastating consequences of stress on the body and the brain – particularly among the most vulnerable.

Claire J. Hanley, Lecturer in Cognitive Neuroscience & Ageing, Swansea University

This article was originally published on The Conversation. Read the original article.

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