Short CommunicationYounger subjective age is associated with lower C-reactive protein among older adults
Introduction
Markers of systemic inflammation, such as C-reactive protein (CRP), are linked to a range of poor health-related outcomes in old age. Elevated CRP is associated with an increased risk of cardiovascular disease (Cushman et al., 2005), stroke (Kaptoge et al., 2010), cancer (Allin et al., 2009), and all-cause mortality (Zacho et al., 2010). With advancing age, higher CRP is also associated with functional limitations (Figaro et al., 2006, Verghese et al., 2012) and cognitive impairment (e.g., Noble et al., 2010). A growing body of research suggests that psychosocial factors may contribute to levels of CRP (e.g., Lewis et al., 2010, Sutin et al., 2010). The present study examined whether subjective age, how old or young individuals experience themselves to be relative to their chronological age, may be one of these factors.
There are age-related changes in immune function (Muller and Pawelec, 2014), including an increase in CRP with aging (Woloshin and Schwartz, 2005). However, aging not only refers to an objective count of years since birth, but also to a subjective evaluation. Subjective age is a crucial construct in gerontology and related disciplines that may potentially contribute to the understanding of immunosenescence, given its implications for a range of health-related outcomes in old age. A younger subjective age is associated with better physical and cognitive functioning (Stephan et al., 2013, Stephan et al., in press) and longevity (Kotter-Grühn et al., 2009), whereas feeling older than one’s age is a risk factor for mortality (Uotinen et al., 2005). Of note, these associations persist even when controlling for chronological age (Stephan et al., in press, Kotter-Grühn et al., 2009). Although this growing body of research implicates subjective age in health among older adults, no study has examined its association with inflammatory markers.
There are several reasons to expect a link between subjective age and CRP. Subjective age tracks individual differences in physical and psychological aging (Bergland et al., 2014, Infurna et al., 2010, Kleinspehn-Ammerlahn et al., 2008) that are associated with inflammation. More specifically, a younger subjective age reflects fewer chronic conditions and better physical health (Bergland et al., 2014, Infurna et al., 2010, Kleinspehn-Ammerlahn et al., 2008) and is related to lower obesity risk (Stephan et al., in press). This better physical health profile is known to translate into lower systemic inflammation (Choi et al., 2013, Kaptoge et al., 2010). In addition, individuals who feel younger than their age tend to have fewer depressive symptoms (Infurna et al., 2010), which have been associated with lower CRP (Howren et al., 2009). Therefore, compared to their age peers with an older subjective age, individuals who feel younger are likely to have higher homeostatic reserves, resulting in less inflammation. Furthermore, the behaviors associated with subjective age may also contribute to systemic inflammation: a younger subjective age is related to engagement in physical activity (Caudroit et al., 2012, Stephan et al., in press), which is related to reduced CRP (Hamer et al., 2012).
Using data from a large national sample of older adults, the present study examines the association between subjective age and CRP. Because of its association with better physical and mental health (Bergland et al., 2014, Infurna et al., 2010, Keyes and Westerhof, 2012), and with health-promoting behaviors (Stephan et al., in press), we expected a younger subjective age to be related to lower CRP. In addition, we tested whether this association held true when physical (e.g. chronic conditions and BMI), mental (e.g. depressive symptoms), and behavioral (e.g. smoking, physical activity) variables were included as covariates.
Section snippets
Participants
Participants were drawn from the Health and Retirement Study (HRS), a nationally representative longitudinal study sponsored by the National Institute of Aging (Grant No. NIA U01AG009740) and conducted by the University of Michigan, and included Americans ages 50 and older and their spouses. A random one-half of the HRS sample was pre-selected for an enhanced face-to-face interview in 2006, which included biomarker measurements and a psychosocial questionnaire that was completed at home and
Results
Table 1 shows the descriptive statistics for all study variables. As expected, the regression analysis indicated that subjective age was negatively related to CRP, controlling for the demographic variables (Table 2): participants who felt younger than their chronological age had lower CRP. The size of this association was stronger than that of education, sex, and age, and was almost comparable to ethnicity (see Table 2). In the second model, the magnitude of the association between subjective
Discussion
Based upon a large national sample of older adults, the present study revealed that the subjective experience of aging, indexed by how old or young individuals feel, is associated with systemic inflammation. Consistent with our hypothesis, a younger subjective age was related to lower CRP, even when controlling for demographic, health-related and behavioral covariates. Furthermore, compared to those who feel older, individuals who feel younger than their age have a lower risk of exceeding the
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