psychological stress, suffered as a result of adverse early experiences, is likely to increase
people’s vulnerability to immune dysregulation in adulthood (Fagundes, Glaser and
Kiecolt-Glaser, 2013; Miller, Chen and Parker, 2011).
Stress and respiratory infectious illness
Over the last 25 years, Sheldon Cohen, a psychologist at Carnegie Mellon University
in the USA, has explored the extent to which psychological and social factors influence
susceptibility to infectious illnesses such as the common cold (see Cohen, 2005, for a
review). As part of this work, Cohen and his colleagues have developed a unique
prospective study design in which healthy participants are exposed to a virus that causes
the common cold. Participants are then monitored following exposure in order to
determine who develops a respiratory illness and reports cold-like symptoms. At
baseline, participants also normally complete a range of psychological measures to assess
their current level of perceived stress, their mood and any recent stressful life events.
In 1991, Cohen and his colleagues published a seminal paper, in the prestigious
journal, The New England Journal of Medicine, in which they demonstrated for the first
time that increases in psychological stress are associated with increases in risk for
developing a cold after exposure to a cold virus. If this is not impressive enough, they
also demonstrated that this association was independent of the participants’ baseline
levels of specific antibody, age, sex, education, allergic status and body mass index
and the season of the year. In addition, they also explored whether the increased
susceptibility was related to changes in stress-related health behaviours such as smoking,
exercise and diet. None of these variables explained the relationship.
In a subsequent study, Cohen and colleagues (1998) concentrated on identifying
the types of stressful life events that were most predictive of increased susceptibility to
infectious illness. In order to do this, these researchers conducted detailed interviews
with each of the participants who took part in their standard prospective design and
found two types of stressful life events were most strongly related to susceptibility. The
first type of event was enduring (1 month or longer) interpersonal problems with family
and friends. The second type was enduring problems associated with work (such as
under- or unemployment). They also found that the longer the stressful event had
lasted, the greater was the risk of developing an infectious illness.
Similar to their earlier study, the authors again examined which psychological and
biological factors may be mediating the effects of psychological stress on increased
susceptibility (see Focus 5.2). Interestingly, they found that regular exercise, non-
smoking and greater sleep efficacy (per cent of time in bed sleeping) were associated
with lower susceptibility to developing a common cold. In addition, they also found
that higher levels of adrenaline and noradrenaline (in the urine in the past 24 hours)
were related to greater susceptibility. However, surprisingly, the effects of these
factors were independent of the relationship between psychological stress and risk of
developing a cold.
In the last 15 years, research has turned its attention to exploring the role of pro-
inflammatory cytokine regulation in explaining the mediating pathways between
psychological stress and the common cold. You will recall from earlier that cytokines
are produced in response to infection. They are also believed to trigger symptoms
associated with upper respiratory infections such as the common cold and the influenza
34 BIOLOGICAL BASES OF HEALTH AND ILLNESS