Stress accelerates aging of the immune system, increasing risk of cancer and heart disease: study

Social stress can accelerate aging of the immune system, according to a new U.S. study. (Gord Altmann / Pexels)

Social stress, such as that resulting from traumatizing events, work anxiety, everyday worries and discrimination, can accelerate aging of the immune system, according to a new study that suggests this may potentially increase one's risk of cancer, cardiovascular disease and illness from infections, including COVID-19.

The study, conducted by researchers out of University of Southern California (USC), suggests this may explain age disparities in illnesses, such as the unequal death toll of the pandemic on seniors.

"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," said lead author and USC postdoctoral scholar Eric Klopack in a press release.

He added that the findings clarify the "mechanisms" involved in accelerated immune aging, and can help to identify points of intervention.

The findings were published Monday in peer-reviewed journal Proceedings of the National Academy of Sciences.

Researchers say the immune system "naturally begins a dramatic downgrade" as people age in a condition known as immunosenescence. When a person grows older, their immune system weakens because there are too many "worn-out" white blood cells circulating and not enough "fresh" white blood cells or T cells to take on new invaders, according to the study.

While this weakening of the immune profile is linked with cancer and heart disease, researchers say it is also associated with increased risk of pneumonia, reduced efficacy of vaccines and declining organ function.

To analyze what accounts for drastic health differences in same-age adults, researchers looked at exposure to stress, which is a known contributor to poor health and robustness of the immune system.

To calculate exposure to social stress, researchers analyzed 5,744 adults over the age of 50 in the U.S. Those involved in the study were tasked with answering a questionnaire inquiring about their experiences with stress, including stressful life events, chronic stress, everyday discrimination they faced as well as lifetime discrimination.

Researchers also examined blood samples from the participants in a lab technique know as "flow cytometry," which counts and classifies blood cells as they pass in a single stream in front of a laser.

The study found that those with higher stress scores had immune systems that showed lower percentages of fresh T cells -- those ready to fight diseases -- and higher percentages of worn-out white blood cells.

According to the report, the link between stress and fewer fresh T cells remained apparent even after accounting for education, smoking, drinking, body mass index and race or ethnicity in participants.

HOW TO ADDRESS AGING IMMUNE SYSTEMS

While some sources of stress may be out of one's control, researchers suggest there may be a workaround for certain forms.

According to the study, T cells mature in the thymus gland, which sits in front of and above the heart. As people age, researchers say the tissue in the thymus shrinks and is replaced by fatty tissue which causes reduced production of immune cells. Other studies have shown that this is accelerated by lifestyle choices such as poor diet and low exercise, both of which are also linked as an effect of stress.

"In this study, after statistically controlling for poor diet and low exercise, the connection between stress and accelerated immune aging wasn't as strong," Klopack explained in the release. "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."

Researchers suggest that improving diet and exercise behaviours in older adults may help to offset the immune system aging associated with stress.

The study authors say cytomegalovirus (CMV) -- a common, usually asymptomatic virus -- may also be a target for intervention.

Once CMV is in a person’s body, it stays there for life and can reactivate. Much like shingles or cold sores, CMV is predominantly dormant but is known to flare up when a person is experiencing high stress, according to the study.

Researchers found that statistically controlling for CMV positivity also reduced the connection between stress and accelerated immune aging.

With this in mind, the study's authors say widespread CMV vaccination could be a "relatively simple and potentially powerful intervention" to help reduce the immune aging effects of stress.