Personality and medication non-adherence among older adults enrolled in a six-year trial.

Health is profoundly influenced by personality, a relationship most established with the five-factor model (FFM) of personality (Costa & McCrae, 1997; Goldberg, 1993; Marshall, Wortman, Vickers, Kusulas, & Hervig, 1994). FFM factors – Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness – are empirically derived clusters of dispositional tendencies that parsimoniously capture the major axes of psychological and behavioural variation in humans (Krueger, Caspi, & Moffitt, 2000; Watson & Hubbard, 1996). FFM factors have been linked with many health-related behaviours and outcomes (Bogg & Roberts, 2004; Chapman, Duberstein, & Lyness, 2007; Friedman, 2000; Roberts, Kuncel, Shiner, Caspi,&Goldberg, 2007), including medication non-adherence (Table 1). Table 1 Prior studies examining associations between FFM personality factors and medication non-adherence Medication non-adherence is common and associated with suboptimal health outcomes (DiMatteo, 2004; DiMatteo, Giordani, Lepper, & Croghan, 2002; Vik, Maxwell, & Hogan, 2004; Vik et al., 2006). Commonly studied correlates of non-adherence – increasing age, male gender, non-white race, lower income, depressive symptoms, obesity, smoking, cognitive impairment, disease burden, and lower social support (Briesacher, Gurwitz, & Soumerai, 2008; Gellad, Haas, & Safran, 2007; Molloy, Perkins-Porras, Strike, & Steptoe, 2008; Salas et al., 2008; Sayers, Riegel, Pawlowski, Coyne, & Samaha, 2008; Vik et al., 2004) – explain only part of the variance in adherence behaviour (Curtis et al., 2009). Disparate studies have linked non-adherence both with general psychological stress and health- and treatment-related cognitions, such as illness perceptions, self-efficacy, and perceived medication necessity and effectiveness (Chia, Schlenk, & Dunbar-Jacob, 2006). FFM factors efficiently capture much of the variance in these characteristics and thus may help unify the diffuse literature on this topic (Conard & Matthews, 2008; Costa, Somerfield, & McCrae, 1996; Sorensen, Duberstein, Chapman, Lyness, & Pinquart, 2008). The 10 prior studies exploring associations between FFM factors and medication non-adherence had relatively small sample sizes, wide variation in participant health conditions, and yielded mixed findings (Table 1). Non-adherence has been associated with lower levels of Conscientiousness in six studies, higher levels of Neuroticism in three studies, and lower levels of Agreeableness and Extraversion in one study each (Table 1). All but one study focused on samples with mean ages in range of 20–50 years, so their applicability to older adults is unclear. All studies were either cross-sectional or longitudinal lasting 1 year or less. The lack of longer follow-up is problematic, since most medications prescribed to older adults are for chronic conditions (Machlin, Cohen, & Beauregard, 2008). Finally, prior FFM analyses failed to account for most of the aforementioned covariates commonly associated with non-adherence, so it is unclear whether FFM factors are independently associated with medication non-adherence at any age. To address these limitations, we examined the relationship of FFM factors to medication non-adherence in a subset of participants in the six year Ginkgo Evaluation of Memory (GEM) study (DeKosky et al., 2006). Based on the literature summarized above, we hypothesized medication non-adherence would be significantly associated with lower levels of Conscientiousness (e.g., less reliability, diligence, and health consciousness; Costa & McCrae, 1997; Goldberg, 1993; Marshall et al., 1994); and higher levels of Neuroticism, since individuals who are more distress prone would be expected to experience disproportionately negative emotions in response to the minor inconvenience of daily pill taking. For the remaining FFM factors, we did not have specific hypotheses, since they exhibited little consistent relationship with non-adherence in prior studies. Our analyses adjusted for patient socio-demographic factors (age, gender, race/ethnicity, education, income), health characteristics (self-rated health, disease burden, smoking status, body mass index (BMI), depressive symptoms, cognitive functioning), and social contact – all of which have been linked with medication non-adherence in prior studies.