• A study in the Proceedings of the National Academy of Sciences found that chronic stress may accelerate the aging of the immune system.
• Researchers found an association between higher levels of social stress and lower levels of T-cells, an important part of the immune system.
• Habitual exercise, and other healthy lifestyle factors, help support a strong immune response.

Whether you’re feeling economic strain, professional challenges, family troubles, or relationship spirals, stress is a normal part of everyday life—at least to some degree. But when it becomes chronic, that can lead to profound changes in how your immune system operates, according to a study in the Proceedings of the National Academy of Sciences.

Researchers looked at more than 5,700 U.S. adults over age 50 and assessed their relationship to what’s called social stress—discrimination, chronic stress, difficult life events, and trauma—and compared that to immune response measured through blood tests.

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Specifically, they measured the percentage of T-cells, which the thymus gland produces. These cells make up an important component of immunity because they help fight off infection. As people age, tissue in the thymus gland shrinks, resulting in reduced production of T-cells, which is one reason why older people may be at higher risk of disease development.

Those with higher stress levels in the study had “older” immune systems, with lower amounts of T-cells. Most notably, they had less of what’s called “naive T-cells,” which haven’t yet encountered antigens like viruses and bacteria. These are short-lived, which means new ones need to be generated regularly for optimal immune function.

“Ideally, you want to have a large, diverse group of these naive T-cells so that they can be ready to respond to new threats you haven’t encountered before, including novel threats like COVID-19, as well as new vaccines,” lead author Eric Klopack, Ph.D., researcher at the Leonard Davis School of Gerontology at the University of Southern California, told Bicycling. “Everyone tends to have fewer naive cells as they get older, but we found this process may be accelerated by social stress.”

It’s not stress on its own that’s zapping your thymus and its powerful cells, though. Rather, in other research, Klopack found an association between high levels of stress and poor diet and sedentary behavior. Both of these factors have a negative effect on the thymus and can lead to fewer naive T-cells being produced, he added.

“While our results suggest that addressing social stress may slow down the immune aging process, observational studies like this one are not able to clearly establish cause and effect, so randomised clinical trials will be needed to make that connection,” said Klopack. “However, interventions that target diet and exercise, as well as reductions in drinking and smoking, may help slow immune ageing.”

Good news for cyclists: Exercise, in particular, has been shown in previous research to support immune system function. For example, a review published in Clinical and Experimental Medicine in 2021 looking at viral infections—and COVID-19 specifically—found that exercise modulates immunity in a way that can lower incidence of infections, and also decrease symptom intensity if you do get sick.

Also, while it may be true that intense training can have a negative impact on the immune system in the short term, according to a review published in the Journal of Sport and Health Science in 2019, that research indicates habitual exercise improves immune regulation overall—and that can slow down the onset of age-related health risks.