The past few years have been nothing if not stressful, with the pandemic bleeding into the invasion of Ukraine, rising inflation, and general concerns around the cost of living. Research from USC highlights how this can accelerate the aging of the immune system, which in turn can have numerous consequences, including heightening our risk of developing cardiovascular diseases and cancer.

The researchers believe that their findings can go some towards explaining the disparities in age-related health that are evident across society, and were especially visible during the Covid pandemic.

“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,” the researchers say. “This study helps clarify mechanisms involved in accelerated immune aging.”

Worsening immunity

The weakening of our immune system as we age is a natural process called immunosenescence. This is largely because our immune system contains too many weakened white blood cells in relation to fresh and strong white blood cells to tackle any invaders.

What is less well understood is why some people have very different health outcomes despite being the same age as healthier peers. The researchers tested to see whether exposure to stress over our lifetime, which is known to contribute to poor health, also affects the vitality of our immune system.

They analyzed data from the University of Michigan’s Health and Retirement Study, which examines the health, economic, marital, and family status of around 5,700 older Americans. Each participant was asked to complete a questionnaire designed to gauge their daily stress levels. Blood samples were also taken from the volunteers and analyzed via flow cytometry, which counts and classifies blood cells.

Stressed out

The results show that people with higher stress scores also seemed to have older-seeming immune systems. This meant that they had a lower percentage of fresh white blood cells and a higher ratio of worn-out blood cells.

Thankfully, exercise and diet may provide a degree of protection, as T-cells are a crucial part of our immune system. They mature in the thymus, which is just above the heart. As we age, the tissue in our thymus tends to shrink and get replaced by fatty tissue, which in turn reduces the production of immune cells. Diet and exercise can slow this process.

“In this study, after statistically controlling for poor diet and low exercise, the connection between stress and accelerated immune aging wasn’t as strong,” the researchers explain. “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.”