By Christian Jarrett

Your personality describes your behavioural tendencies, your habits of thought and ways of relating to the world. For instance, some of us find it a lot harder to keep our negative emotions in check, which is measured by the Big Five personality trait of neuroticism (or “emotional instability”). It seems logical that people with this kind of disposition might be more prone to developing mental health problems like anxiety and depression, and indeed many studies suggest this to be the case.

From a scientific perspective, however, it’s not clear which comes first: perhaps mental health problems contribute to a more neurotic personality, or maybe living through adversity contributes to a neurotic personality and mental health difficulties.

An important new study in European Archives of Psychiatry and Clinical Neuroscience helps clarify the picture because it is the first, to the researchers’ knowledge, to look simultaneously at people’s personality, life events and mental health problems as they unfold over time. Though they come with important caveats, the findings suggest that some people have a personality profile that predisposes them to mental health problems, to more serious mental health problems when they occur, and even to more adverse life events.

The data come from a cohort of nearly 600 participants in Switzerland, who were first interviewed in 1979 when they were aged 19 to 20 about their mental health, any problems with drugs or alcohol, and their family background. The researchers led by Michael Hengartner at Zurich University then interviewed the same group again about their mental health and any experiences of relationship break-up and/or job loss in 1981, 1988, 1993, 1999 and finally in 2008 (now aged 50 years, 335 of the original sample were still participating).

The participants also completed measures of their personality in 1988 when they were aged 29-30 and again in 1993 when aged 34-35: specifically, these questionnaires revealed their levels of aggressiveness (including lack of self-control), extraversion (how cheerful and self-confident) and neuroticism (including their day-to-day emotional instability and propensity to worry).

Even after controlling for family background and education, the researchers found that personality – averaged across the two times it was measured – was strongly related to the likelihood of experiencing mental health problems through the study: for instance, higher neuroticism was associated with increased odds of depression and anxiety and drink or drug problems. Higher extraversion, by contrast, was associated with less risk of mental health problems.

Quantifying the personality-mental health link, the researchers said that “persons scoring high on aggressiveness and neuroticism and low on extraversion had an approximately 6 times increased risk for internalising disorder [a catch-all term for various depression and anxiety-related conditions] compared to persons scoring low on aggressiveness and neuroticism and high on extraversion”.

Adverse life events were also associated with risk of mental problems: for example, and perhaps unsurprisingly, participants who endured job losses and relationship breakups were more likely to develop major depression.

But personality and life events were not independent factors. Personality was related, albeit weakly, to the likelihood of experiencing negative life outcomes: participants who scored higher on aggressiveness were more likely to go through job losses and relationship breakups through the course of the study, and higher scorers on neuroticism were more likely to go through job losses.

Moreover, adverse life events were more strongly associated with future mental health problems for participants with more neurotic personalities. And finally, when mental health problems occurred, they tended to be more severe for participants with more neurotic personalities (differences in trait neuroticism accounted for over half the variation in severity of problems between participants).

“Our findings stress the fundamental role of personality, mainly neuroticism, for the occurrence, persistence and severity of psychopathology [i.e. mental health problems]” the researchers said, adding: “Our data further highlight that the relationship between critical life events and psychopathology is at least in part moderated by personality.”

These new findings complement recent research that’s shown that many of the same genes that influence personality are also involved in mental health disorders. They also dovetail with the recent finding that psychotherapy is associated with reductions in trait neuroticism, and with a new study out of Sweden involving over a million men that found their teenage personality, especially their neuroticism, was related to their future chances of being diagnosed with severe mental health problems.

Hengartner and his team make no claims about the precise nature of the cognitive and neural mechanisms that might underlie a neurotic personality and a vulnerability to mental health problems, but they propose that the personality-mental health link can be understood in terms of “life history strategy” – an idea from evolutionary biology that notes how some of us follow a fast strategy (a short-term approach to life which can pay off in high risk environments), whereas others follow a slow strategy (playing a longer, more patient game). Seen this way, people with more impulsive, nervous, aggressive personalities are well-adapted for the fast life, but at the cost of being at much greater risk for mental health problems.

All of this comes with some weighty caveats, most notably that despite the longitudinal nature of this study, it’s still not proven which way the causal arrow points between the different factors involved. In particular, it’s unfortunate that the first personality measure wasn’t taken until the participants were aged 29, raising the possibility that participants’ personalities had already been shaped by mental health issues and life events before that time (though the researchers argue this is unlikely, especially in light of past research showing that personality traits are relatively stable through young adulthood. In other words, they think their participants’ traits as measured at age 29 and 34 are probably much the same as they would have been if measured at the start of the study at age 19/20).

Another limitation is that because of its roots in the 1970s and 80s, the study depended on personality measures that are now somewhat obsolete; in particular some aspects of personality such as Openness were not studied at all.

“A strong association between personality and psychopathology may imply causation, but this is not necessarily true,” the researchers admitted. “Genetically and environmentally informed long-term prospective studies beginning in childhood are, therefore, required to better understand the causal role of personality traits in the occurrence and course of severe psychopathology.”

If this idea that some people’s personalities render them more vulnerable (to mental health problems and adverse life events) is borne out by future research, it could allow help and support to be targeted at those likely to be need it most. It also raises the interesting question of whether future mental health problems might be averted by helping youth to develop more resilient personalities.

—Articulation and testing of a personality-centred model of psychopathology: evidence from a longitudinal community study over 30 years

Christian Jarrett (@Psych_Writer) is Editor of BPS Research Digest