As we age, our immune system begins a downgrade in performance, a condition called immuno-senescence.

This entails a progressive reluctance for older, worn-out white blood cells to retire from circulation, while there are “too few fresh, ‘naïve’ white blood cells ready to take on new invaders”.

This ‘immune ageing’ is associated not only with cancer, “but with cardiovascular disease, increased risk of pneumonia, reduced efficacy of vaccines and organ system ageing”.

While this decline is inevitable, it happens at different rates for different people. Why is that?

A new study finds that stress – in the form of traumatic events, job strain, everyday stressors and discrimination – is a powerful accelerator of this decline, thereby increasing our risk of serious illness.

Lead study author Eric Klopack, a postdoctoral scholar in the University of Southern California’s Leonard Davis School of Gerontology, 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.”

So what was the study?

First, 5744 study participants over the age of 50 answered a questionnaire “designed to assess respondents’ experiences with social stress, including stressful life events, chronic stress, everyday discrimination and lifetime discrimination”.

Then, blood samples from the participants were 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.

In other words, an audit was taken of the participants’ immune system by counting the number of worn-out blood cells against the number of fresh and efficient white blood cells.

The researchers specifically examined T-cells, a type of white blood cells, which are a vital part of the immune response to viral infections and foreign bodies.

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”.

The researchers say 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”.

More about T-cells

T-cells mature in the thymus, a gland that sits behind the breast bone.

As we get older, healthy tissue in the thymus is replaced by fatty tissue, and this results in reduced production of immune cells.

The authors of the new study cite past research that found this deterioration of the thymus and subsequent loss of immune cells “is accelerated by lifestyle factors like poor diet and low exercise, which are both associated with social stress”.

“In this study, after statistically controlling for poor diet and low exercise, the connection between stress and accelerated immune ageing wasn’t as strong,” Dr Klopack said.

“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 ageing.”

The point being?

Dr Klopack says that improving diet and exercise behaviours in older adults “may help offset the immune ageing associated with stress”.

Another potential target for intervention is the cytomegalovirus (CMV), a common, usually asymptomatic virus in humans “known to have a strong effect in accelerating immune ageing”.

Like shingles or cold sores, CMV is a member of the herpes family and lies dormant most of the time.

It can flare up, “especially when a person is experiencing high stress” and you’ll suffer a mild flu-like illness for a few days, sometimes weeks.

The authors suggest that widespread CMV vaccination “could be a relatively simple and potentially powerful intervention that could reduce the immune ageing effects of stress”.

Good idea, but there are no available vaccines for CMV.

There is plenty of research and development in play, “with the hope and expectation that it will be available in the next five to 10 years”.