A comprehensive analysis finds that people with mental and neurodevelopmental disorders are about 50% more likely to be left-handed or mixed-handed than those without such diagnoses. The large synthesis draws on data from more than 202,000 individuals across 402 datasets and highlights a potential link between brain lateralization and mental health risk. The work is published in Psychological Bulletin and integrates findings from ten previous meta-analyses plus 33 newly released studies. Researchers tracked how handedness intersected with age, sex, diagnosis, and measurement methods to build a clearer picture of this complex relationship.
For Thai readers, where right-handedness is the norm, the study underscores a meaningful connection between how the brain develops and conditions such as schizophrenia, autism spectrum disorder, and intellectual disability. Recognizing this link could help reduce stigma around non-right-handedness and inform educational and health policies as Thailand strengthens youth mental health initiatives.
Handedness refers to a person’s preferred hand for daily tasks like writing and eating. It results from a mix of genetics and environment and develops early in life, reflecting brain organization that supports language and motor control. While past work suggested atypical brain asymmetry might accompany unusual hand preference and higher risk of certain disorders, this large-scale synthesis provides a broader perspective on the relationship.
The analysis was led by a team using a second-order meta-analysis approach: they combined results from ten prior meta-analyses and incorporated 33 newly published datasets. The study encompassed more than 202,000 participants around the world, with careful attention to how handedness was measured and how diagnoses were categorized.
Key takeaways show that individuals with mental health or neurodevelopmental conditions were about 50% more likely to be non-right-handed than those without such diagnoses. Mixed-handedness—where there is no consistent hand preference—showed the strongest association. The link was most pronounced for schizophrenia, autism spectrum disorder, and intellectual disability, while conditions like depression and dyscalculia did not show significant differences from healthy peers.
Neurodevelopmental conditions such as ADHD, autism, dyslexia, intellectual disability, and childhood stuttering reported the highest rates of non-right-handedness. This supports the idea that early brain development influences both hand preference and vulnerability to certain developmental and mental health challenges. Language-related conditions, including dyslexia and autism, showed particularly strong associations, aligning with the understanding that left-hemisphere brain regions govern language and often relate to right-hand use.
According to researchers, these findings support the hypothesis that atypical brain lateralization reflects deeper neurodevelopmental differences linked to language and mental health risk. In the Thai context, where left-handedness has historically faced social barriers and practical challenges in school settings, the study offers a chance to reframe handedness as part of natural brain diversity rather than a marker of deficiency.
The study does not claim that handedness causes mental health issues or vice versa. Instead, both may arise from shared neurodevelopmental factors that influence hemispheric balance. Experts caution against using these insights to label or stigmatize left-handed individuals. Instead, they emphasize the value of understanding brain development as a spectrum that can inform supportive educational strategies and early interventions.
For Thailand, these insights could inform more sensitive school screenings and inclusive education practices. Handedness could become one among several indicators guiding early support for learning or communication challenges, helping educators tailor assistance to each student’s needs. Public awareness campaigns can also normalize brain diversity, reducing stigma around non-right-handedness and related conditions.
Thai schools have long wrestled with the social impressions of left-handedness, sometimes encouraging a switch to the right hand. The latest findings advocate a shift toward recognizing neurodiversity and focusing on each child’s developmental trajectory. This approach could improve inclusive education and mental health support in Thai society, especially as youth mental health remains a priority after pandemic-related stress and rising reports of learning difficulties.
A limitation noted by researchers is the predominantly binary treatment of handedness (right, left, or mixed). They recommend future studies adopt continuous, nuanced measures to capture the full spectrum of hand preference.
Practical takeaways for Thai parents, teachers, and policymakers include fostering openness toward handedness differences, promoting acceptance of brain diversity, and integrating handedness-related questions into early developmental screenings. Most importantly, schools should avoid pressuring left-handed students to conform and instead address each student’s unique learning and communication needs. Building an inclusive environment will help all children reach their potential, regardless of hand dominance.
Data from reputable health and research institutions worldwide underscore the evolving understanding of brain development and its impact on education and mental health. In Thailand, continued collaboration between the Department of Mental Health, educational authorities, and research platforms will help translate these findings into actionable practices for schools, clinics, and communities.