Age and the association between negative affective states and diurnal cortisol

Research attests to age-related strengths in affective experience. Negative affect (NA) decreases across the life-span, whereas positive affect (PA) remains relatively stable, showing declines only in very late adulthood (see reviews by Charles & Carstensen, 2007; Consedine & Magai, 2006). The theory of Strength and Vulnerability Integration (SAVI; Charles, 2010; Charles & Piazza, 2009) posits that these empirical findings reflect increases in older adults’ motivation to maintain affective well-being, as well as age-related improvements in the ability to effectively employ emotion regulation strategies. According to SAVI, age-related strengths in emotion regulation are adaptive because sustained physiological arousal from NA becomes more costly with increasing age (Charles, 2010). This increased cost is due to the body becoming less resilient over time, which makes it difficult for people to adjust to the sustained physiological arousal caused by NA. In the current study, we test aspects of SAVI by examining whether sustained levels of NA (as indicated by high mean levels of daily NA) are related to a worse physiological outcome among older adults compared to their younger counterparts. We use the hormone cortisol as a biomarker with which to test this hypothesis. Age and Cortisol Cortisol, the end-product of the HPA-axis, is vital for many physiological processes, such as immune system modulation, blood pressure regulation, and glucose metabolism (Lovallo & Tomas, 2000). Cortisol follows the same diurnal pattern across age groups (Van Cauter, Leproult, & Kupfer, 1996), sharply increasing within one hour after waking and steadily declining thereafter, until reaching a nadir in the late evening hours (Lovallo & Thomas, 2000). With age, however, the decline in cortisol observed across the course of the day is attenuated, resulting in a higher end-of-day nadir (for review, see Piazza, Almeida, Dmitrieva, & Klein, 2010; Raff et al., 1999; Yen & Laughlin, 1998). Older age is also related to higher basal levels throughout the day (Chahal & Drake, 2007; for review, see Epel, Burke, & Wolkowitz, 2009), such that mean cortisol levels are estimated to increase between 20% and 50% from the age of 20 to the age of 80 (Van Cauter, et al., 1996). Although research attests to age-related changes in diurnal cortisol, considerable heterogeneity exists within age groups, some of which may be attributable to indices of emotional well-being. For example, although mean levels of cortisol increase with age, older adults who engage in effective coping strategies have lower total daily cortisol output than older adults who do not engage in effective coping strategies (O’Donnell, Badrick, Kumari, & Steptoe, 2008). Similarly, the cortisol awakening response is elevated among lonelier older adults (e.g., Adam, Hawkley, Kudielka, & Cacioppo, 2006) and among those who report having low social status (Wright & Steptoe, 2005) compared to their more socially connected peers. To the extent that more effective coping strategies, decreased loneliness, and higher social status are associated with lower levels of sustained distress, these findings point to the role of better HPA-functioning among older adults who experience less NA compared to those who experience more NA. No study, however, has explicitly examined whether sustained levels of NA may create within-group differences that are larger among increasingly older adults. In other words, it is unclear if same-aged individuals who experience different levels of average NA (e.g., low versus high) show different cortisol profiles, and--if so--whether this association becomes stronger with increasing age. Affect and Cortisol Studies examining the association between affect and cortisol indicate that sustained negative mood states are linked to higher levels of cortisol and cortisol dysregulation. At the extreme, clinical affective disorders such as depression are associated with dysregulated patterns of cortisol (Bremmer et al., 2007; Burke, Davis, Otte, & Mohr, 2005; Mantella et al., 2008). At non-clinical levels of distress and with more transient measures of NA, findings are mixed. A number of studies have revealed an association between elevated levels of daily NA and increased diurnal cortisol (e.g., Adam, et al., 2006; Smyth, et al., 1998). For example, in their ecological momentary sampling study, Smyth and colleagues found that higher levels of NA were associated with higher levels of cortisol across the day (Smyth et al., 1998). Other studies, however, have failed to detect associations between daily NA and cortisol (Ice, 2006; Polk, Cohen, Doyle, & Skoner, & Kirschbaum, 2005; Simpson et al., 2008). One possible reason for these discrepant findings is that minor fluctuations in NA may not be strong enough to consistently elicit changes in levels of cortisol. Alternatively, the effects of these minor fluctuations may vary according to how much NA an individual experiences on average. Adjusting to elevated daily NA may be particularly difficult for people who, in general, experience high levels of NA. For these individuals, the wear-and-tear of additional NA may be exacerbated, particularly among older adults who also face the physiological vulnerabilities associated with aging. It is also possible, however, that people who experience high levels of average NA reach a ceiling effect of sorts, whereby additional NA may not elicit as large of a cortisol response as it does in people who experience low levels of average NA. Moreover, these individuals may show evidence of physiological inflexibility, such that even on days when they do not experience high daily NA, their levels of cortisol may be heightened. Of the previous studies that have explored associations between naturally-occurring affective states and cortisol, many have done so with age ranges spanning fewer than 20 years (e.g., Adam et al., 2006; Steptoe, Wardle, & Marmot, 2005). Other studies have examined wider age ranges, but have focused either on individuals younger than approximately 60 years of age (e.g., Jacobs et al., 2007; Polk et al., 2005; van Eck, Berkhof, Nicolson, & Sulon, 1996) or on more transient assessments of NA among those older than approximately 60 years of age (e.g., Evans et al., 2007). Moreover, many studies have focused on laboratory-based experiments that examine acute response to NA, rather than naturally-occurring mood states (e.g., e.g., Hatzinger, Brand, Herzig, & Holsboer-Trachsler, 2011; Kudielka, Buske-Kirschbaum, Hellhammer, & Kirschbaum, 2004). These studies have greatly informed the literature; yet, to truly understand the associations between daily NA, average NA, and age, it is necessary to use a large data set that includes multiple measures of NA and participants spanning across a wide age range. The current study utilizes such a data set to examine whether there are associations between daily NA and average (or sustained) NA, and whether this association changes as a function of age. The Current Study We examine the links between diurnal cortisol and negative affective states in individuals spanning five decades of life (ages 33–84), who completed a series of daily diary interviews. Given that our measure of NA assessed affective experience across the day and was usually reported at the end of the day, we examined cortisol measures across similar timeframes - total cortisol output across the course of the day (area-under-the-curve with respect to ground, AUCg) and bedtime cortisol - as opposed to assessments prior to the affective experience (i.e. upon awakening). We did, however, also explore the association between affect and cortisol at these earlier time points. Based on SAVI, we hypothesized the following: Hypothesis 1 High levels of NA will be associated with higher levels of total daily cortisol output (AUCg), but these associations will increase in magnitude with age Hypothesis 2 High levels of NA will be associated with elevated levels of bedtime cortisol, but these associations will increase in magnitude with age. We also examined the interaction between daily and average NA for both AUCg and bedtime cortisol to see if the interaction between these two experiences becomes more costly (e.g., results in higher levels of cortisol) among successively older adults.