776 vII. APPLICATIONS  AND  IMPLICATIONS
behavior in others (e.g., hostility) are linked 
reciprocally to personality and to health 
through health behaviors and psychophysi -
ology.
Sophisticated models also take into ac -
count the fact that biological changes and 
the experience of disease can influence per -
sonality. For example, brain impairment 
(from injury or disease) can alter an individ -
ual’s personality. And deteriorating health 
can affect personality as a result of conse -
quent illness-  related unemployment, social 
isolation, drug use, or depression. Not only 
are the relations reciprocal, but they also 
may progress and change across time.
Health behaviors and individual pat -
terns, as well as health indices (e.g., blood 
pressure, cortisol levels, immune responses, 
lipid levels, and body mass index [BMI]), 
are all dynamic variables. When snapshots 
of the association between personality and 
such health variables are examined in cross- 
sectional studies, they do not take into ac -
count the rising or falling trajectories of per -
sonality or health variables. Cross-  sectional 
designs do not identify reciprocal influences 
between personality and health, and they do 
not place these snapshots in the broader con -
text of longer-  term trends. Valid models of 
personality and health need a longitudinal 
perspective, as personality, health, and the 
intervening mechanisms are moving targets.
Modern conceptions of personality as an 
evolving biopsychosocial cluster of traits, 
motivations, abilities, and behavior patterns 
are very well suited to this dynamic lifespan 
approach. Cognitive–  motivational, social–  
emotional, and situational–  behavioral influ -
ences on clusters of dynamic outcomes are 
comfortable concepts in modern personality 
research. Yet the lifespan approach to the 
study of personality and health is a rela -
tively new development (Friedman, 2000; 
Smith & Spiro, 2002). In this chapter, we 
draw inferences about the “dynamisms” and 
“tropisms” of the mechanisms unfolding 
over time that explain the observed relations 
between personality and health (Friedman, 
2000).
Dynamic Lifespan Approaches
Developmental psychology was transformed 
by the adoption of a lifespan perspective (Baltes & Goulet, 1970; Baltes, Reese, & 
Lipsitt, 1980), and the study of personality 
and health is in the midst of a similar revolu -
tion. Ultimately, research on personality and 
health has two core purposes. On the practi -
cal side, there is a wish to find interventions 
that can promote health and longevity. On 
the conceptual side, there is a desire to un -
derstand better what it means to be a healthy 
person across time. Both involve illuminat -
ing the pathways to good health as people 
age. In particular, life-  course epidemiology 
informs the development of the theoretical 
underpinnings of lifespan models of person -
ality and health (Kuh & Ben-  Shlomo, 1997; 
Krueger, Caspi, & Moffitt, 2000; Lynch & 
Davey Smith, 2005; Smith & Spiro, 2002). 
Two models are particularly relevant to per -
sonality and health: critical period models 
and accumulation models.
Critical Period  Models
Critical (or sensitive) period models assert 
that exposure to risks during critical peri -
ods of development have long-  lasting effects 
and more pronounced effects than exposure 
at other points in the lifespan. For example, 
young children exposed to the poverty and 
stress associated with their family’s low so -
cioeconomic status (SES) at this time were 
more likely to succumb to upper respiratory 
infections in adulthood than those not so 
exposed (Cohen, Doyle, Turner, Alper, & 
Skoner, 2003). Some of the earliest work 
along these lines showed that poor nutrition 
during the prenatal period or infancy raises 
the risk of coronary heart disease decades 
later (Barker, 1995; Barker, Osmond, For -
sén, Kajantie, & Eriksson, 2005). This work 
was a shock to the cardiology community, 
because it questioned the focus on concur -
rent and short- to medium-  term risk factors. 
Such models are in striking contrast to the 
common assumption that one is healthy 
until afflicted by disease over some relatively 
short period of time.
Particular levels of a trait at certain peri -
ods in life, such as high levels of “difficult 
temperament” in childhood, might increase 
the individual’s vulnerability to disease pro -
cesses or to behaviors or environments that 
will eventually damage body systems. For 
example, high levels of sensation seeking in 
adolescence could increase vulnerability to 