We have known for some time that stress affects our immune systems. Many studies have shown that stress can suppress the immune system, but other studies have shown boosts in the immune system under stress. A July 2004 meta-analysis of 293 studies conducted over the past 30 years puts the pieces of the puzzle together. Psychologists Suzanne Segerstrom, Ph.D., and Gregory Miller, Ph.D. found the following:
- Stress does indeed affect the immune system in powerful ways.
- Short-term stressors boost the immune system. It seems that the “fight or flight” response prompts the immune system to ready itself for infections resulting from bites, punctures, scrapes or other challenges to the integrity of the body.
- Chronic, long-term stress suppresses the immune system. The longer the stress, the more the immune system shifted from they adaptive changes seen in the “fight or flight”1 response to more negative changes, first at the cellular level and later in broader immune function. The most chronic stressors – stress that seems beyond a person’s control or seems endless – resulted in the most global suppression of immunity. Almost all measures of immune system function dropped across the board.
- The immune systems of the elderly or those already sick are more subject to stress-related changes.
In reaching these conclusions the authors looked at the effects of the various stressors on different immune responses, such as “natural” and “specific” immunity. They summarized the results of the studies that looked at each of these types of stress:
Natural immunity produces quick-acting, all-purpose cells that can attack many pathogens; they bring fever and inflammation.
The body takes a few days to mount a more specific attack on particular invaders with specific immunity. This response includes lymphocytes (T-cells and B cells). Specific immunity has both cellular responses, which fight pathogens that get inside cells (such as viruses), and humoral responses, which fight pathogens that stay outside cells, such as bacteria and parasites. Segerstrom and Miller were able to assess how different types of immune response correlated with different types of stress because researchers have identified the blood markers of these different immune responses.
They divided stressors into different types:
Acute time-limited stressors: lab challenges such as public speaking or mental math.
Brief naturalistic stressors: real-world challenges such as academic tests.
Stressful event sequences: a focal event such as loss of a spouse or major natural disaster gives rise to a series of related challenges that people know at some point will end.
Chronic stressors: pervasive demands that force people to restructure their identity or social roles, without any clear end point – such as injury resulting in permanent disability, caring for a spouse with severe dementia, or being a refugee forced from one’s native country by war.
Distant stressors: traumatic experiences that occurred in the distant past yet can continue modifying the immune system because of their long-lasting emotional and cognitive consequences, such as child abuse, combat trauma or having been a prisoner of war. Much of their analysis goes on to review the similarities and differences among the 293 studies that they examined. These studies included a total of 18,941 subjects. “Stressful event sequences” appeared to be weakly associated with different immune consequences, depending on the type of event. There appeared to be different patterns for grief than for trauma, for example, but the associations weren’t strong enough for the authors to make new claims. They recommended further study.
The authors did find that the most chronic stressors - those which change people’s identities or social roles, are more beyond their control and seem endless - were associated with the most global suppression of immunity. In such situations almost all measures of immune function dropped across the board. The longer the stress, the more the immune system shifted from potentially adaptive changes (such as those in the acute “fight or flight” response) to potentially detrimental changes, at first in cellular immunity and then in broader immune function. This analysis suggests that stressors that turn a person’s world upside down and appear to offer no hope for the future probably have the greatest psychological and physiological impact.
The authors also found that age and disease status affected a person’s vulnerability to stress-related decreases in immune function. It seems that illness and age make it harder for the body to regulate itself.
This is a ground-breaking meta-analysis that helps us understand the complex relationship between stress and the immune system. It should lead to new treatments and to better stress management programs, especially for patients with HIV or other disorders that compromise immunity.
Reference: Segerstrom & Miller, 2004. Psychological Stress and the Human Immune System: A Meta-Analytic Study of 30 Years of Inquiry Psychological Bulletin, 130, 4.
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