As people age, their immune systems naturally begin to decline. This aging of the immune system, called immunosenescence, may be an important part of such age-related health problems as cancer and cardiovascular disease, as well as older people’s less effective response to vaccines.
But not all immune systems age at the same rate. In our recently published study, my colleagues and I found that social stress is associated with signs of accelerated immune system aging.
Stress and immunosenescence
To better understand why people with the same chronological age can have different immunological ages, my colleagues and I looked at data from the Health and Retirement Study, a large, nationally representative survey of U.S. adults over age 50. HRS researchers ask participants about different kinds of stressors they have experienced, including stressful life events, such as job loss; discrimination, such as being treated unfairly or being denied care; major lifetime trauma, such as a family member’s having a life-threatening illness; and chronic stress, such as financial strain.
Recently, HRS researchers have also started collecting blood from a sample of participants, counting the number of different types of immune cells present, including white blood cells. These cells play a central role in immune responses to viruses, bacteria and other invaders. This is the first time such detailed information about immune cells has been collected in a large national survey.
As people age, the T cells in the immune systems become less effective at fighting pathogens.
National Institute of Allergy and Infectious Diseases/Flickr, CC BY-NC
By analyzing the data from 5,744 HRS participants who both provided blood and answered survey questions about stress, my research team and I found that people who experienced more stress had a lower proportion of “naive” T cells – fresh cells needed to take on new invaders the immune system hasn’t encountered before. They also have a larger proportion of “late differentiated” T cells – older cells that have exhausted their ability to fight invaders and instead produce proteins that can increase harmful inflammation. People with low proportions of newer T cells and high proportions of older T cells have a more aged immune system.
After we controlled for poor diet and low exercise, however, the connection between stress and accelerated immune aging wasn’t as strong. This suggests that improving these health behaviors might help offset the hazards associated with stress.
Similarly, after we accounted for potential exposure to cytomegalovirus – a common, usually asymptomatic virus known to accelerate immune aging – the link between stress and immune cell aging was reduced. While CMV normally stays dormant in the body, researchers have found that stress can cause CMV to flare up and force the immune system to commit more resources to control the reactivated…
