Personality and inflammatory markers

1. Personality and inflammatory markers René Mõttus   Michelle Luciano  John M. Starr  J. F. Price*  Ian J. Deary Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, UK  *Centre for Population Health Sciences, University of Edinburgh, UK

2. What's the big deal? • If any associations occur, this is not (necessarily) trivial: • Personality traits = responses to questionnaire items • Inflammatory markers = biomarkers measured in blood • If the associations are not trivial, they might be informative: • Inflammatory markers indicate various aspects of ill-health, markers of disease burden, increase with age • Personality traits summarize consistent and stable ways of feeling, thinking and behaving • personality → ill-health • ill-health → personality • common causes for both

3. It's nice to have them, but it's just as nice to see them go away • If something breaks the associations, this might be an explanation: • Controlling for smoking makes personality irrelevant for inflammation: personality traits may incline people towards the bad stuff, which in turn makes people ill • Probably suggestive of personality causing health • So we may end up with a better understanding of why some people are more ill than others (from the health perspective)  • Or we may understand where and how personality traits matter (from the personality science perspective)

4. What has been found so far on personality and inflammation? Hardly anything breath-taking: • Few studies available • Very small effects (who would expect more anyway?) • Conscientiousness, Openness, and Neuroticism may be related to inflammatory markers • Openness may be confounded by intelligence or education • Little evidence for mediators

5. There is no way these effects could ever be detected on a sample of a few hundred people

6. What we had and did • A large older sample • Lothian Birth Cohort 1936 – 1,091 people (aged ~70+) • Various inflammatory markers, measured twice over 3 years • Possibility to test for possible mediators and control for confounders • Smoking, drinking, physical activity • Emotional distress • Cognitive ability, education, social class, BMI, diseases • A "replication sample" – nearly 1,000 older people with diabetes (Edinburgh Type 2 Diabetes Study)

7. LBC1936 • For Conscientiousness, the associations with inflammation were to some extent consistent over time and markers   • The most consistent correlate being Conscientiousness is in line with most previous findings*  • Intellect apparently had spurious association with inflammation • Oh yeah, the effect sizes were tiny (but no one expected otherwise)     * maybe not type a 1 error after all

9. ET2DS – the diabetes sample [Nothing]

10. Bad practicies of science • We had a "replication sample"  • It didn't replicate • So the “hits” [significant findings in LBC1936] had apparently been rubbish (type 1 errors) • Or ... maybe we had chosen a bad "replication sample" • Should we forget that we had the bad "replication sample"? • Or, the non-replication might actually be the most informative aspect of the study, once there is an explanation for that

11. Might actually be interesting stuff • People with diabetes constantly monitor their health themselves or get it monitored by health carers • Problems are addressed quickly  • They are offered a lot of medical advice • All that happens regardless of their levels of Conscientiousness -- they need to take care or they die • So, maybe self-monitoring and willingness to promptly address any symptoms of illness is the thing that makes Conscientiousness matter for health in normal people

12. Perhaps not the final truth • Generates some hypotheses to be tested though, at the very least • self-monitoring, problem-addressing and looking for help as mediators could be measured (somehow)