When stress is good for you: straining to stave off cognitive decline

Exercising to the point where your body is under mild to moderate pressure can, among many benefits, help to stimulate DNA repair and add years to your life 

After 30, our total mass of muscle fibres gradually diminishes and is accelerated if we lead a mostly sedentary existence. Picture: iStock

We have long been told that being too stressed out can be seriously damaging, but a growing body of research is showing that we need a certain degree of mental and physical strain in our lives to stay healthy, especially as we get older.

One of the first experts to suggest that stress could offer positive benefits was American psychiatrist Firdaus Dhabhar, who now runs a research laboratory studying stress and resilience at the University of Miami. As Dhabhar explained in a 2009 TED talk, spikes of short-term stress were initially developed as a way of helping our ancestors fend off predators.

This mild to moderate stress can help to keep our body’s processes functioning sharply, from the immune system to the muscles and the brain. “Whether stress is detrimental or beneficial all comes down to the duration of stress,” Dhabhar says.

“Short-term stress lasting from minutes to hours has positive effects, while chronic stress persisting from months to years, can harm us.”

The need for regular bursts of short-term stress can be seen most acutely in our muscles, which require frequent stimulation in the form of exercise. After 30, our total mass of muscle fibres gradually diminishes for the remainder of our lives, and is accelerated if we lead a mostly sedentary existence.

Andy Philp, who heads the biology of ageing programme at the Centenary Institute in Sydney, says that from the age of 50 onwards, people who exercise regularly can limit their muscle loss to 0.1% per year, while those who do nothing at all may lose up to 2% a year.

“Everyone’s muscle will get smaller and weaker, that’s just part of the biological ageing process,” he says. “But if you think about that rate of loss, you can have quite manageable, healthy ageing versus severe, accelerated ageing.”

Exercise not only influences the amount of muscle we have, but it is also crucial for maintaining the connection between the muscles and the nervous system. This interaction becomes less efficient without regular use, making our reactions sluggish and increasing our vulnerability to falls.

Stress systems

Joanna Kacprzyk, a cell biologist at University College Dublin, explains that stressing the body’s systems through regular, moderate exercise has benefits which can be seen at a molecular level, increasing the levels of antioxidant enzymes, stimulating DNA repair mechanisms and reducing inflammation. This helps lower what scientists call our biological age, even though our chronological age is steadily increasing.

“There is a lot of evidence that over time, a sedentary lifestyle is linked with accelerated accumulation of cellular damage and makes us age faster,” says Kacprzyk. “Exercise activates protective mechanisms in our cells and consequently delays ageing.”

As we age, studies have repeatedly shown how it tends to be a case of use or lose it. Researchers from the Irish Longitudinal Study on Ageing found that over 50s experiencing difficulty walking 100 metres or finding it hard to lift 10 pounds (4.5kg) were at an increased risk of dying in the following four years.

Some forms of exercise are essential in providing the stimulation our body needs to keep going, most notably resistance or strength training, which can be done through lifting weights or activities such as cycling. A study funded by the Irish Research Council found that men and women over 65 who did aerobic exercise – such as moderate walking or swimming – and resistance training had improved fitness and muscle strength levels than those who did aerobic exercise alone.

Brendan Egan, an exercise physiologist at Dublin City University, who was involved in the study, says that some form of strength training is particularly crucial because so few of us partake in this form of exercise as we age. “It is consistently observed that middle to older age adults with the greatest amount of muscle size, the strongest leg, chest or grip strength, best balance, or best performance in tasks, like repeatedly rising from a chair or climbing stairs, are those that are best protected from disease and death in later life, and these abilities are all associated with the benefits of strength training,” he says.

The most famous example of how resistance training can help to lower biological age is the French cyclist Robert Marchant, a World War II veteran who lived to the age of 109 before passing away in May 2021. Marchant took up competitive cycling aged 68 and was still setting records at 105. Scientists who studied his physiology found he had comparable cardiovascular fitness to men aged 42 to 61.

Cognitive decline

Cognitive decline is not inevitable but just as various forms of exercise-induced stress can keep us from physically declining as we age, stress can also prevent us from losing our mental faculties. While most of us might complain about the stress of our jobs, this plays a significant role in keeping our brains sharp and active. Research suggests that people who continue to work at least part-time later in life are less vulnerable to cognitive decline.

One extensive study of nearly half a million self-employed workers in France found that delaying retirement significantly decreases the risk of developing dementia. This is thought to be because the regular bursts of stress resulting from work deadlines and interactions with colleagues stimulate stem cells in the brain to generate new neurons and strengthen the connections between existing brain cells.

Just as muscle mass shrinks with age, we also lose brain cells as we get older. From age 40 onwards, the brain slowly atrophies, with its size decreasing by approximately 5% per decade, a rate of decline which accelerates sharply after age 70. But there are still many ways for elderly adults to get the requisite brain stimulation to avoid atrophy. Volunteering or attempting to learn a new skill in your 80s and 90s can play a significant role in keeping your brain young.

Joyce Shaffer, a psychiatrist and behavioural scientist at the University of Washington in Seattle, highlights the power of listening or playing music. She says it offers a total brain workout, stimulating multiple different regions at the same time, including those responsible for memory, movement and mood.

“Individuals of any age listening to music learn things faster,” says Shaffer. “Studies have even found older individuals that start to take piano lessons for the first time when they’re already in their 80s, it can improve their brain function.”

Of course, stress can have negative impacts, especially those that do not go away. People who are chronically stressed due to their job, family life or financial situation experience a notable effect on their health. The resulting chronic inflammation increases their propensity to develop obesity, heart disease, diabetes, and depression.

Scientists are increasingly investigating the possible benefits of moderate stress across various aspects of medicine, particularly those connected to the immune system. A clinical trial conducted by Guy’s & St Thomas’ Charity in London found that mild exercise can make chemotherapy more effective in fighting tumours and minimising its damaging impact on the body’s healthy tissues. At the same time, research has shown that moderate stress could help boost the safety and effectiveness of vaccines.

“The human body is very responsive, or adaptable, to changes in activity of our muscles,” says Egan. “At a fundamental level, exercise is a transient stress that the body adapts to by becoming stronger or fitter when that stress is applied often and in the right manner. Without that stress, there is no adaptation and improvement in function or capacity.”