OBJECTIVES: Holding positive beliefs about illness and having an optimistic outlook have been associated with increased well-being across a range of health conditions. However, research has indicated that being very optimistic may not actually be beneficial, and holding a realistic attitude is more adaptive in some forms of chronic illness, for example, Parkinson's disease (PD). This study aimed to explore the nature of relationships between illness perceptions, optimism and well-being: specifically, whether a linear or non-linear relationship best described the data. Additionally, the proposed moderating effect of optimism on the relationship between illness perceptions and well-being was tested.

DESIGN: A total of 109 participants with idiopathic PD completed questionnaire measures of illness perception, optimism, mood and health-related quality of life (HRQoL).

METHODS: Multiple regression analyses were used to explore relationships between illness perceptions, optimism, mood and HRQoL. The potential curvilinear effects of illness perceptions and optimism were modelled using squared variables and linear and quadratic curve estimation.

RESULTS: Holding positive illness perceptions predicted better well-being. Some evidence for a non-linear relationship between optimism and mood was found. Optimism had a significant moderating effect on the relationship between specific illness perceptions and outcome.

CONCLUSIONS: Optimism appears to provide protection against some negative perceptions of illness and was associated with better mood and HRQoL. The findings indicate that specific illness perceptions may be beneficial targets for therapy. Therapeutic interventions should focus on enhancing positive perceptions of PD but potentially more importantly general optimistic attitude to maximize well-being.

STATEMENT OF CONTRIBUTION: What is already known on this subject? Positive illness perceptions and high optimism are associated with better well-being in a range of conditions, both chronic and acute. Preliminary studies suggest that in chronic degenerative diseases, marked positive optimism confers no additional benefit over medium levels of optimism for well-being and is associated with less use of adaptive coping. What does this study add? Optimism moderates the effects of specific negative illness perceptions on well-being in Parkinson's disease. No evidence was found that unrealistic positive illness perceptions are detrimental to well-being. Adaptive illness perceptions may be condition specific.