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104 Biobehavioral Resilience to Stress

self-reported physical health (Scheier et al., 1989); lower blood pressure and
reduced rehospitalization risk following coronary vascular surgery (Scheier
et al., 1999); buffering blood pressure responses to violence exposure (Clark,

Benkert & Flack, 2006); higher natural killer cell cytotoxicity (NKCC) in
HIV+ women (Byrnes et al., 1998) and men with prostate cancer (Penedo
et al., 2006); lower HIV viral load among gay men (Milam, Richardson,
Marks, Kemper & McCutchan, 2004); and lower mortality in patients
with head and neck cancers (Allison, Guichard, Fung & Gilain, 2003). On

the other hand, different investigators have failed to find an association

between optimism and reduced mortality in lung cancer patients (Schofi eld
et al., 2004) and CD4 count among HIV+ gay men (Tomakowsky, Lumley,
Markowitz & Frank, 2001).
To delineate the diff erential effects of optimism on coping with brief ver-

sus long-term stress, Cohen et al. (1999) followed a cohort of 39 women for
3 months and measured their NKCC, CD4, and CD8 T cell sublets. Using
an autoregressive linear model, the authors found that optimism moder-

ated immune outcomes differentially in response to acute versus persistent

stressors. Specifically, while optimism buffered immune response parameters

following exposure to acute stress, optimists also had more immune decre-
ments than pessimists upon exposure to chronic stress (Cohen et al., 1999).
Sieber et al. (1992) studied changes in NKCC in adult males after exposure to

controllable and uncontrollable stresses (noise) and found that subjects who
perceived that they had control over the stressor did not show any reduction

in NKCC. However, optimism amplified the detrimental effects of uncon-

trollable stress on NK activity. Segerstrom, Taylor, Kemeny, and Fahey (1998)

argued that negative effects of optimism on the immune system might be
explained by “the engagement hypothesis,” which asserts that optimistic (ver-
sus pessimistic) people remain engaged with stressful conditions for longer

periods of time. For example, when highly difficult research subjects are given
or impossible anagrams are to be solved, optimism serves to increase their
task engagement time and skin conductance, and recovery levels of salivary
cortisol (Nes, Segerstrom & Sephton, 2005). Segerstrom, Taylor, Kemeny, and
Fahey (1998) speculated that optimism may enhance immunity by enabling
early termination of response to relatively easy or straightforward stress
via problem- solving, but that immune dysfunction occurs as the result of
prolonged exposure to persistent, chronic, or complex stress. In other words,
optimism may facilitate allostasis when the stressors are brief and simple, but
may increase allostatic load when stressors are chronic and complex.

Additional support for the moderating effects of optimism can be found
in studies of baseline and stress-induced cortisol levels. Lai et al. (2005) found
that subjects with higher optimism scores also had lower cortisol secretion
in the mornings. Creswell et al. (2005) have observed that the affi rmation of
personal values prior to stress exposure is associated with lower subsequent

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