Temperament has been defined as “an individual’s propensity to react emotionally, learn behavior and to form attachments without conscious effort by associative conditioning,” wrote Aleksi Ahola, PhD, of the University of Oulu, Finland, and colleagues. “Temperament is a potential endophenotype for depression, as it is inheritable and genetically linked with depression,” they said. The Temperament and Character Inventory (TCI) includes four temperament traits: harm avoidance (HA), novelty seeking (NS), reward dependence (RD), and persistence (P); previous studies have shown associations between higher HA and depression, but long-term data are limited, they wrote.
In a population-based study published in Comprehensive Psychiatry, the researchers followed 3,999 adults from age 31 to 54 years. The participants were part of the Northern Finland Birth Cohort 1966 Study.
The primary outcome was the onset of depression in a previously mentally healthy adult population. Temperament was assessed using the TCI, and depression was based on the Hopkins system checklist-25 (SCL-25). Individuals with previous psychiatric disorders related to depression, bipolar disorder, or psychosis were excluded. Effect size was measured using the Cohen’s d test.
Overall, 240 individuals were diagnosed with depression over the follow-up period. Women later diagnosed with depression had higher baseline TCI scores for HA, compared with those without depression. After controlling for multiple variables, higher TCI scores for HA, NS, and P were significantly associated with increased risk of any depression.
Among men, the TCI HA score was associated with significantly increased risk of any depression after adjustments, but no association appeared for other TCI scores. However, higher RD was associated with a reduced risk of psychotic depression in men (odds ratio, 0.79), although the study was not designed to assess psychotic depression, the researchers noted.
In an additional analysis of temperament cluster groups, shy and pessimistic traits were associated with depression in men (OR, 1.89), but not in women. In women, the cluster group with no specific extreme personality traits (cluster III) appeared to show an association with depression, which may be related to the association of NS and P with depression, the researchers wrote in their discussion.
The study is the first known to show differences between genders in the prediction of depression based on temperament traits, notably the link between high persistence and the onset of any depression in women, they said.
The study findings were limited by several factors including the potential for missed cases of less severe depression not reported in a national register, and by the relatively small number of men in the study, the researchers noted. In addition, the TCI’s three character traits of self-directedness, cooperativeness, and self-transcendence were not part of the current study, they said.
However, the results were strengthened by the large sample size, premorbid temperament assessment, and long follow-up period, although more research is needed in larger populations using real-world personalities to confirm the findings, they said.
“Research regarding temperament is important as it may have clinical significance as predictor of psychiatric morbidity and even suicide risk,” they said.
“Understanding those potentially at risk of depression could help in preventing the onset of the disease, and creating cluster profiles to match real-world personas could offer a clinical tool for this kind of prevention,” they concluded.
The study was supported by the University of Oulu, Oulu University Hospital, the Ministry of Health and Social Affairs, the National Institute for Health and Welfare, and the Regional Institute of Occupational Health. The researchers had no financial conflicts to disclose.