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Personality and Individual Differences
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Caffeine, stress, and proneness to psychosis-like experiences: A preliminary investigation Simon R. Jones *, Charles Fernyhough
Department of Psychology, Durham University, South Road, Durham DH1 3LE, UK
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In diathesis–stress models of psychosis, cortisol released in response to stressors is proposed to play a role in the development of psychotic experiences. Individual differences in cortisol response to stressors are therefore likely to play a role in proneness to psychotic experiences. As caffeine has been found to increase cortisol response to a given stressor, we proposed that, when levels of stress were controlled for, caffeine intake would be related to hallucination-proneness and persecutory ideation. Caffeine intake, stress, hallucination-proneness and persecutory ideation were assessed by self-report questionnaires in a non-clinical sample (N = 219). Caffeine intake was positively related to stress levels and hallucinationproneness, but not persecutory ideation. When stress levels were controlled for, caffeine intake predicted levels of hallucination-proneness but not persecutory ideation. Implications of these ﬁndings are discussed and avenues for future research suggested. Ó 2008 Published by Elsevier Ltd.
Article history: Received 8 July 2008 Received in revised form 15 October 2008 Accepted 31 October 2008 Available online 19 December 2008 Keywords: Coffee Hallucination Persecutory ideation Psychosis Schizophrenia Tea
1. Introduction Diathesis–stress models of psychosis propose that stress may play a contributory role in the development of hallucinations and delusions, typically associated with the schizotypal/schizophrenia spectrum (Neuchterlein & Dawson, 1986). Cortisol has been highlighted as having a key role in translating the experience of psychosocial stressors into the biological factors associated with psychosis (Walker & Diforio, 1997). It therefore seems likely that factors causing individual differences in cortisol response to stressors will inﬂuence the likelihood of developing hallucinatory or delusional experiences. One such factor is caffeine, which has been found to cause an increase in the amount of cortisol released in response to a stressor (Lane, Adcock, Williams, & Kuhn, 1990). Although daily usage of caffeine creates a reduction in this effect, caffeine intake in habitual users still enhances the cortisol response to stress (Lovallo et al., 2005). As such, caffeine intake may be associated with greater proneness to psychotic experiences due to its enhancement of the cortisol response to stress. We hence ﬁrstly hypothesised that, for a given level of stress, caffeine intake would be associated with greater levels of proneness to psychotic experiences. Controlling for stress levels is also necessary due to caffeine consumption increasing when individuals are stressed (Ratliff-Crain & Kane, 1995). We secondly hypothesised that caffeine intake would inter* Corresponding author. Tel.: +44 1913 343240; fax: +44 1913 343241. E-mail address: email@example.com (S.R. Jones). 0191-8869/$ - see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.paid.2008.10.032
act with stress, with caffeine intake being more strongly associated with proneness to psychotic experiences when levels of stress were high. No studies have yet tested such a hypothesis. Existing studies of the relation between caffeine and the positive symptoms of schizophrenia (e.g., clinically relevant hallucinations and delusions) have produced mixed ﬁndings. Studies that have experimentally altered caffeine intake in patients with schizophrenia, by switching patients to decaffeinated coffee for a period of weeks, show conﬂicting results. Whilst some...