One of the most fascinating aspects of mind-body research concerns the link between personality and health. Numerous studies show that optimists live longer and are healthier than their pessimistic counterparts (for more information, see WDDTY vol 18 no 6)-and, now, new evidence suggests that extro-verts may be better off, too.
The recent study, by researchers from the University of Rochester Medical Center in New York, NY, has confirmed that extroverts, particu-larly those with high "dispositional activity" or engagement in life, have dramatically lower levels of the inflammatory chemical interleukin-6 (IL-6) in their blood (Brain Behav Immun, 2009; 23: 636-42).
IL-6 is an important indicator of stress, and raised levels have been linked to several inflammatory diseases such as rheumatoid arthritis and coronary heart disease (Ann Intern Med, 1998; 128: 127-37; Atherosclerosis,
2000; 148: 209-14). IL-6 is also highly predictive of mortality, with the risk of death reportedly doubling at levels greater than 3.19 picograms (pg)/mL (Am J Med, 1999; 106: 506-12).
Using the well-known Neuroticism -Extroversion-Openness Five-Factor Inventory (NEO-FFI), a personality questionnaire designed to assess extroversion, neuroticism, openness, agreeableness and conscientious-ness, the Rochester study sought to determine whether or not certain personality traits were associated with IL-6 levels in a racially diverse sample of 103 urban-dwelling primary-care patients.
Extroversion was defined as a trait with three distinct parts: a tendency towards happy thoughts; a desire to be around others; and high levels of 'dispositional energy'-a sense of vigour or active engagement with life ("I'm bursting with energy; my life is fast-paced"). Although the first two parts were not related to IL-6, there was a statistically significant association between IL-6 and the activity component of extroversion. What's more, the difference between high and low dispositional energy was enough to push IL-6 levels over the 3.19 pg/mL threshold at which the mortality risk was doubled. This suggests that those who have less vitality for life-what French philosopher Henri Bergson called 'elan vital ('life force')-may be heading for an early grave.
What is not clear, however, is whether low levels of 'dispositional activity' are causing inflammation, or whether inflammation takes its toll on people by reducing these personality tendencies.
The findings could also be explained by exercise. Having a higher level of dispositional energy may indicate greater participation in physical activity, so it may be the exercise that's bringing the benefits. Indeed, daily physical activity has been linked with lower IL-6 levels in older adults.
Still, the team is not convinced that exercise represents the whole answer. According to Benjamin Chapman, the lead researcher in the study, "Beyond physical activity, some people seem to have this innate energy separate from exer-cise that makes them intrinsically involved in life." Perhaps it is this 'elan vital that is playing a health-protecting role (Brain Behav Immun, 2009; 23: 636-42).
As well as apparently protecting against stress-related inflammation, extroversion is also associated with a host of other benefits. Sociability and positive emotions, for instance-other facets of extroversion-have been associated with greater resistance to the common cold (Psychol Sci, 2003; 14: 389-95; Psychosom Med, 2003; 65: 652-7). Positive emotions are also linked to higher antibody production in response to hepatitis B vaccination (Health Psychol, 2001; 20: 4-11).
Extroversion appears to fend off dementia, too. In a study of more than 500 older adults followed for six years, those who scored high for extroversion and low for neuroticism (being easily distressed) proved to have the lowest dementia risk of all participants (Neurology, 2009; 72: 253-9).
So, how can we all benefit from these findings-including those of us who are simply more introverted by nature? You don't need to change your personality completely. The trick is to incorporate the key components of extroversion into your life: think positively; keep connected; and stay energetic and engaged with life.
For more information on positivity and connectedness, see WDDTY vol 18 nos 5 and 6.
Neuroticism and health
Another personality trait that appears to be related to health is neuroticism, or emotional instability. Neurotic people have a tendency to think negatively and are easily distressed. Neuroticism has been associated with:
- mild cognitive impairment, or MCI (Neurology, 2007; 68: 2085-92)
- Parkinson's disease (Eur J Neurol, 2008; 15: 1148-54)
- chronic fatigue syndrome (Health Psychol, 2008; 27: 369-78)
- ulcers (Health Psychol, 2008; 27: 369-78)
- coronary heart disease (Health Psychol, 2008; 27: 369-78)
- death due to coronary heart disease (Psychosom Med, 2007; 69: 923-31).
Vol. 20 05 August 2009