Season of birth effect on personality in a general population.

Seasonality of births in schizophrenia and other mental disorders has been consistently observed. This may be through effects of unknown environmental factors that seasonally fluctuate on the brain development. The effects may affect cognitive function of the brain and behavioral characteristics that might be correlated with the development of personality not only in patients with mental disorders but also in healthy subjects. We, therefore, investigated the effects of season of birth on personality traits in healthy Japanese adults (n = 397). Personality traits were evaluated using the NEO Personality Inventory-Revised (NEO PI-R). A trend for lower Agreeableness in subjects born during winter (December to February) than other subjects was observed (P = 0.036, after correction for the multiple testing, multiple regression analysis adjusting for age and sex). Other major factors of the NEO PI-R, including Neuroticism, Extraversion, Openness and Conscientiousness, were not affected by season of birth. Further studies may be recommended to confirm the results, considering the relatively limited sample size. Evaluation of cognitive functions and behaviors using other measures including event-related potentials and functional MRI may also help the interpretation of the present result.