Sustained psychological stress is well known to correlate with poor health and accelerated manifestations of aging, when looking at the epidemiology of sizable study populations. Here, researchers link stress to the age-related decline of the immune system, an important aspect of aging that affects tissue function throughout the body. It is tempting to point to inflammatory signaling as the mechanism of importance, but the conclusion here is that the effects of stress on health are in large part mediated by poor lifestyle choices, such as a worse diet and less exercise, that in turn produce a worse metabolism and more rapid degenerative aging.
To measure exposure to various types of social stress, the researchers analyzed responses from a national sample of 5,744 adults over the age of 50. They answered a questionnaire designed to assess respondents' experiences with social stress, including stressful life events, chronic stress, everyday discrimination, and lifetime discrimination. Blood samples from the participants were then analyzed 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, naive T cells remained strong even after controlling for education, smoking, drinking, BMI, and race or ethnicity.
Some sources of stress may be impossible to control, but the researchers say there may be a workaround. 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. "In this study, after statistically controlling for poor diet and low exercise, the connection between stress and accelerated immune aging wasn't as strong. 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."