Stress prematurely weakens the body’s immune system - putting people at greater risk of cancer, heart attacks and infections such as Covid, warns a new study.
Researchers found that traumatic events - such as the death of a loved one - as well as job strain and discrimination accelerate the ageing of the immune system, potentially increasing a person’s risk to a whole range of illnesses including cardiovascular disease.
The American team's findings, published in the Proceedings of the National Academy of Sciences (PNAS), could help explain disparities in age-related health, including the greater toll of the Covid-19 pandemic on the elderly.
Study lead author Doctor Eric Klopack, of the University of Southern California (USC), said: "As the world’s population of older adults increases, understanding disparities in age-related health is essential.
"Age-related changes in the immune system play a critical role in declining health. This study helps clarify mechanisms involved in accelerated immune ageing.”
As people age, the immune system naturally begins a dramatic downgrade, a condition called immunosenescence.
With advanced age, Dr Klopack explained that a person’s immune profile weakens, and includes too many worn-out white blood cells circulating and too few fresh, “naive” white blood cells ready to take on new invaders.
He said: "Immune ageing is associated not only with cancer but with cardiovascular disease, increased risk of pneumonia, reduced efficacy of vaccines and organ system ageing."
The USC researchers decided to see if they could find a connection between lifetime exposure to stress - a known contributor to poor health - and declining vigour in the immune system.
They queried and cross-referenced enormous data sets from University of Michigan’s Health and Retirement Study of the economic, well-being, marital, family status, and public and private support systems of older Americans.
To calculate exposure to various forms of social stress, the team analysed responses from a national sample of more than 5,700 adults over the age of 50.
The participants answered a questionnaire designed to assess respondents’ experiences with social stress, including stressful life events, chronic stress, everyday discrimination and lifetime discrimination.
Blood samples from the participants were then analysed through flow cytometry - a lab technique that counts and classifies blood cells as they pass one-by-one in a narrow stream in front of a laser.
As expected, people with higher stress scores had older-seeming immune profiles, with lower percentages of fresh disease fighters and higher percentages of worn-out white blood cells.
Dr Klopack said: "The association between stressful life events and fewer ready to respond, or naive, T cells remained strong even after controlling for education, smoking, drinking, BMI and race or ethnicity."
Some sources of stress may be impossible to control, but the researchers say there may be a workaround.
Dr Klopack said: "T-cells - a critical component of immunity - mature in a gland called the thymus, which sits just in front of and above the heart.
"As people age, the tissue in their thymus shrinks and is replaced by fatty tissue, resulting in reduced production of immune cells.
"Past research suggests that this process is accelerated by lifestyle factors like poor diet and low exercise, which are both associated with social stress."
He added: “In this study, after statistically controlling for poor diet and low exercise, the connection between stress and accelerated immune aging wasn’t as strong.
“What this means is people who experience more stress tend to have poorer diet and exercise habits, partly explaining why they have more accelerated immune aging.”
He said improving diet and exercise in older adults may help offset the immune ageing associated with stress.
Additionally, he says cytomegalovirus (CMV) may be a target for intervention.
Dr Klopack said: "CMV is a common, usually asymptomatic virus in humans and is known to have a strong effect accelerating immune ageing.
"Like shingles or cold sores, CMV is dormant most of the time but can flare up, especially when a person is experiencing high stress.
"In this study, statistically controlling for CMV positivity also reduced the connection between stress and accelerated immune ageing.
"Therefore, widespread CMV vaccination could be a relatively simple and potentially powerful intervention that could reduce the immune ageing effects of stress."
