High rainfall at birth is associated with raised inattention scores on the Conners adult ADHD rating scale among healthy participants in Japan

IntroductionBirth during the 3 month period ending in August has been associated with increased risk of attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD), especially in regions where the school year starts in September. Nevertheless, few studies have either examined these factors in Japan, where the academic year starts in April, or investigated the role of weather conditions at birth.MethodsWe enrolled 317 healthy adults from a population of medical students. Participants completed the Conners Adult ADHD Rating Scale (CAARS) and the Autism Spectrum Quotient (AQ). From local meteorological records, meteorological data corresponding to each participant's birth month and birth year, such as temperature, sunshine hours, vapor pressure, atmospheric pressure, rainfall, and snowfall were obtained.ResultsNo significant difference in CAARS or AQ scores was found between participants born during June-August versus other months, or between those born during January-March versus other months. Multiple regression analysis revealed higher rainfall at birth as associated with elevated scores on the CAARS.ConclusionsFindings of this study suggest that high rainfall at birth is associated with elevated scores of ADHD symptoms in healthy participants. To clarify the underlying mechanisms, further research with larger, more samples is warranted.