Just as depression has been clearly shown to be related to diabetes and to health in general, there is a growing literature linking both positive and negative affect to health outcomes. Whereas in health literature, depression is more often viewed in terms of DSM IV diagnostic categories and their clinical implications, it is likely as well that subclinical depressive symptoms, distress, mood, and affect may have implications for health outcomes and the general well-being of patients with diabetes. For example, Fisher and colleagues (2007)
reported higher HbA1C among those scoring above a cutoff of 16 and greater on the CES-D, compared to those <16, but no relationship between major depressive disorder (MDD), using a diagnostic interview, and HbA1C.
Measures of affect usually differ from measures of depression not only in the time frame and persistence of specific feelings, but also in the breadth of emotions reflected in the measures. Many measures of affect include both positive affect (PA) and negative affect (NA), usually viewed as two distinct, orthogonal dimensions, rather than opposite ends of a bi-polar dimension. The constructs of positive and negative affect refer more to what Denollet & de Vries (2006)
define as “subjective moods and feelings” (p. 172). They characterize positive affect as pleasant engagement with the environment, including such feelings as happiness, excitement, and contentment. Negative affect reflects distress and unpleasant reaction to the environment, involving such feelings as anger, fear, sadness, and nervousness.
Watson’s Positive and Negative Affect Scale (PANAS) (Watson, Clark, & Tellegen, 1988
) was designed to measure orthogonal dimensions of positive and negative affect and has been widely used in studies of affect and health. When related, NA and PA are usually negatively correlated, although the strength of the correlation varies. Some of the variability in the relationship between the two is probably related to the time frame used as well as the intensity of the feelings (Pressman & Cohen, 2005
; Watson, Wiese, Vaidya, & Tellegen, 1999
). Daily measures of PA and NA tend to be less related to each other, partly because of the typically low to moderate levels of affect reported (Watson et al., 1999
). The exception is in situations of high intensity, where an extreme in one would be incompatible with the other. When the time frame is longer, the correlations may be higher
Depending on the time frame, affect can either reflect a relatively fleeting mood (state affect) or a more stable characteristic of the individual (trait affect). Generally, questions measuring state affect are framed “in the last day” or “currently,” whereas trait affect is usually framed “in the last few weeks” or “generally” (Pressman & Cohen, 2005
). Of course, in daily studies as long as the present one (21 days), daily state affect measured repeatedly over several weeks might approach a typical or trait affect for the individual. A daily diary format allows many of the questions regarding characteristics of affect to be addressed in terms of how people differ in their average levels of PA and NA across the 21 days as well as how individuals vary day to day.
How are NA and PA related to depression? In most studies, affect and depressive symptoms are correlated. For example, Denollet and de Vries (2006)
report a correlation of .58 between NA on the PANAS and depression as measured by the Centers for Epidemiologic Studies Depression scale (CES-D). Very similar results were reported by Watson et al. (1988)
between the PANAS NA scale and the Beck Depression Inventory (r=.57). Although there is far less information on positive affect, Watson et al. report correlations ranging from −.19 to −.36 between PA and depression symptom scales, depending on the depression scale and the time frame used. In a study of older persons that examined both daily affect and depression (CES-D), those who were categorized as having either “major depression” or “other depression” on the CES-D exhibited more NA and less PA (Chepenik et al., 2006
). However, the authors report that even among those with major depression, there was a great deal of day to day variability in NA.
Similar to the models proposed for the relationship between depression and health (e.g., (Cohen, Kessler, & Gordon, 1995
; Kiecolt-Glaser & Glaser, 2002
), the pathways between negative and positive affect and health outcomes may operate through behavioral and/or biological mediators, both of which have relevance for diabetes. Pressman and Cohen (2005)
propose two models for the links between positive affect and health, although one might assume that such models would apply to negative affect as well. First, they suggest that affect has a direct effect on both behaviors and physiology. More specifically, they hypothesized that positive affect should result in better health behaviors and better adherence to treatment regimens. Direct physiological effects could include autonomic nervous system activation, HPA axis activation (decreased cortisol), and an effect on immune functioning (Kiecolt-Glaser, McGuire, Robles, & Glaser, 2002
; Taylor, Repetti, & Seeman, 1997
). Indeed, some evidence exists for a moderating effect of NA on the relationship between PA and natural killer cell activity (Valdimarsdottir & Bougjerg, 1997
In general, evidence is mixed regarding the effects of both positive and negative affect on health. Pressman and Cohen (2005)
summarize the literature as showing that, in general, higher PA is related to lower mortality and morbidity, but point out that the data are often conflicting. Steptoe and Wardle (2005)
found significant relationships for PA in the form of lower salivary cortisol, reduced fibrinogen stress response, and lower ambulatory heart rate (in men only) in an examination of data from the Whitehall study. Looking at NA in relationship to cardiovascular outcomes in a daily study, Kamarck, Schwartz, Shiffman, Muldoon, Sutton-Tyrell, & Janicki (2005)
differentiated between negative affect (valence) and arousal (activation) and found that NA was not related to heart rate changes, but arousal was.
There appears to be little evidence on the relationship between affect and blood glucose levels. In a study of adults with type 1 and type 2 diabetes, Trief, Himes, Orendorff, and Weinstock (2001)
reported that high scores on the PANAS NA scale were related to more reported health problems and poorer marital quality. Although they found that marital quality was not significantly related to HbA1C, they did not report the relationship between affect and glycemic control. Yancura and colleagues, (Yancura, Aldwin, Levenson, & Spiro, 2006
) found no relationship between NA and fasting glucose in a study of metabolic syndrome, but PA was related to glucose. In a review article of research on affect and biological markers of health, Ryff, et al. (2006)
found evidence for a relationship between NA (but not PA) and glycemic control. In conclusion, the evidence is mixed for both PA and NA in their relationship to health, suggesting the need for a closer look at both affect and diabetes outcomes.