New York, June 14 : Stress -- in the form of traumatic events, job strain, everyday stressors and discrimination -- accelerates ageing of the immune system, potentially increasing a person's risk of cancer, cardiovascular disease and illness from infections such as Covid-19, according to a new study. To calculate exposure to various forms of social stress, the researchers from University of Southern California analysed responses from a national sample of 5,744 adults over the age of 50. Their experiences with social stress, including stressful life events, chronic stress, everyday discrimination and lifetime discrimination were compared with blood samples 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. 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, the team revealed in the paper published in the Proceedings of the National Academy of Sciences (PNAS). 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. Improving diet and exercise behaviours in older adults may help offset the immune ageing associated with 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," said lead study author Eric Klopack, a postdoctoral scholar at the University. "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," he added. /IANS