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Senior Citizens More Likely to Suffer Immunity Drop
Under Chronic Stress
Clear patterns emerge outlining
greater damage from chronic stress
July 5, 2004 Stress has long been identified as a
negative factor in the ability of people to fight infection but a new
analysis of years of research have revealed a more detailed picture of
the impact of stress on the immune system, including clear information
that older people are more prone to stress related change in the immune
system.
This major new "meta-analysis" a study of studies
has highlighted patterns of how stress affects human immunity,
strengthening it in the short term but wearing it down over time. Major
findings are three-fold.
> First, the overlapping findings of 293
independent studies reported in peer-reviewed scientific journals
between 1960 and 2001 with some 18,941 individuals taking part in all
-- powerfully confirm the core fact that stress alters immunity.
> Second, the authors of the meta-analysis
observed a distinctive pattern: Short-term stress actually "revs up" the
immune system, an adaptive response preparing for injury or infection,
but long-term or chronic stress causes too much wear and tear, and the
system breaks down.
> Third, the immune systems of people who are
older or already sick are more prone to stress-related change.
Psychologists Suzanne Segerstrom, PhD, of the
University of Kentucky, and Gregory Miller, PhD, of the University of
British Columbia, analyzed the results of the nearly 300 studies by
sorting them into different categories and statistically evaluating
relationships. For example, the five stressor categories included:
> 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.
The psychologists also looked at the effects of the
various stressors on different immune responses, such as natural and
specific immunity. Natural immunity produces quick-acting, all-purpose
cells that can attack many pathogens; they bring fever and inflammation.
While they fight on the front line, the body takes a few days to mount a
more efficient attack on specific invaders via the lymphocytes (T-cells
and B cells) of specific immunity. 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. Scientists have identified the
blood markers of these different immune responses; stress studies
measure them to indicate stress response. As a result, Segerstrom and
Miller were able to assess how different types of immune response
correlated with different types of stress.
Write the authors, "Stressful events reliably
associate with changes in the immune system and
characteristics of those
events are important in determining the kind of change that occurs."
Acute time-limited stressors, the type that produce
a "fight or flight" response, prompted the immune system to ready itself
for infections resulting from bites, punctures, scrapes or other
challenges to the integrity of the skin and blood. In evolution, this
response would be selected as adaptive. Brief stressors enhanced quick,
energy-efficient natural immunity, to help the body meet the challenge
prompting fight or flight. At the same time, certain aspects of specific
immunity that consume time and energy were suppressed.
Stressful event sequences seemed to be weakly
associated with different immune consequences, depending on the type of
event. The data suggested different patterns for bereavement (loss) and
trauma, but the authors didn't see associations strong enough to make
new claims. In this regard, further study is needed.
The most chronic stressors 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;
almost all measures of immune function dropped across the board.
Duration of stress came into play: 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. Thus, stressors that turn a person's world upside down and
appear to offer no "light at the end of the tunnel" could have the
greatest psychological and physiological impact.
Finally, Segerstrom and Miller found that age and
disease status affected a person's vulnerability to stress-related
decreases in immune function. They attribute this to how illness and age
make it harder for the body to regulate itself.
The authors are satisfied that their meta-analysis
confirms the value of looking at stressors and immunity in greater
detail to learn the mechanisms underlying the body's response to stress.
In this case, defining stressor types and examining natural vs. specific
and cellular vs. humoral immune responses turned up useful information.
Says Miller, "A meta-analysis lets you ask questions that are too big
for any one study to answer. You see if things are consistent over the
gamut of labs, methods and people."
Future studies, the authors hope, will look at the
role of behavior in the stress-immunity pathway. For example, optimism
and coping are known to mitigate the immune response to stress. Further,
they write that the most pressing question facing researchers is, "the
extent to which stressor-induced changes in the immune system have
meaningful implications for disease susceptibility in otherwise healthy
humans." The field of psychoneuroimmunology has yet to tie together the
various threads of research to determine whether immune system changes
are the reason that stress makes people more likely to get sick.
The report appears in the July issue of
Psychological Bulletin, which is published by the American Psychological
Association.
Article: "Psychological Stress and the Human Immune
System: A Meta-Analytic Study of 30 Years of Inquiry," Suzanne C.
Segerstrom, Ph.D., University of Kentucky, and Gregory E. Miller, Ph.D.,
University of British Columbia; Psychological Bulletin, Vol. 130, No. 4.
(Full text of the article is available from the APA
Public Affairs Office and at
http://www.apa.org/journals/bul/press_releases/july_2004/bul1304601.html)
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