of data from studies of health and behavior strongly suggests that psychological
processes and emotional states influence the etiology and progression of
disease and contribute to overall host resistance or vulnerability to illness. In
general, psychosocial or behavioral factors exert their influence on health or
illness in three basic ways (e.g. Krantz et al 1985). First, some of these influences
involve direct biological changes that parallel, precede, are induced by,
or occur as part of an emotional reaction or behavior pattern. Research has
shown, for example, that stress involves increases in blood pressure, heart rate,
and sympathetic arousal and is associated with hematological changes that can
contribute directly to heart disease, hypertension, or cardiac events (e.g.
Manuck & Krantz 1984; Patterson et al 1994, 1995; Schneiderman 1983).
Similarly, stress appears to affect the immune system through a complex array
of neural and hormonal pathways (Besedovsky & DelRey 1991, Maier & Watkins
1998). Whether these immune system changes are strong or prolonged
enough to enhance vulnerability to infection or illness is not clear, but they
have been implicated in the etiology and progression of viral infections,
wound healing, cancer, and HIV disease (e.g. Andersen et al 1994, Baum &
Nesselhof 1988, Cohen & Williamson 1991, Kiecolt-Glaser et al 1985).
A second way in which health and disease are influenced is by behaviors
that convey risks or protect against them. Health-enhancing behaviors are activities
that convey health benefits or otherwise protect people from disease.
Health-impairing behaviors are activities that have harmful effects on health.
Diet and exercise are often cited as protective behaviors, and tobacco use and
alcohol abuse as health-impairing behaviors. Diet and exercise can help minimize
the conditions underlying cardiovascular disease and cancer. Tobacco
use is associated with biological changes in the lungs, heart, and other bodily
systems that appear to predispose disease. Similarly, drug use, high-risk sexual
activity, and other potentially harmful behaviors are important mediators of
disease processes.
A third general pathway for behavioral influences on health and illness is
through behaviors associated with illness or the possibility that one is ill. Beginning
with early detection, these influences include secondary prevention,
surveillance, detection and interpretation of symptoms, and the decision to
seek care. Adherence with medical advice or prescription can also affect diag-
nosis and treatment and affect health outcomes. Interference with any of these
can disrupt the process of interpreting and presenting symptoms, obtaining
prompt and effective medical care, and complying with treatment, surveillance,
or prevention regimens.
Elaborations of this basic model of health and behavior have been developed
to help explain the comorbidity of physical and mental health problems
and the etiology and progression of cancer and stress-related diseases (e.g. Andersen
et al 1994, Cohen & Rodriguez 1996). Evidence linking key pieces of
these models has been reported, and although it is far from complete in many
instances, it supports the notion that behavioral variables affect health and illness
at these three different levels. This review considers evidence for this psychosocial
perspective, focusing on major life-threatening illnesses such as cardiovascular
disease, cancer, and HIV disease. Because of its complex role in
health and illness, stress will be considered briefly before turning to evidence
of direct biological effects on health and illness, of indirect and direct effects
of health-impairing behaviors, and of the counter-influence of healthenhancing
behaviors. Health behaviors, particularly adherence and early detection
behavior, are also considered.
