Left-Handed People More Common In Certain Mental Disorders, Major Study Finds

BOCHUM, Germany — Left-handed people appear significantly more often among those with certain mental and neurodevelopmental disorders, according to groundbreaking research that analyzed data from over 200,000 individuals. This connection potentially offers a window into how our brains develop and organize themselves.

Connecting Left-Handedness To Brain Development

The study, published in Psychological Bulletin, revealed that conditions like schizophrenia, autism, and intellectual disability show notably higher rates of left-handedness compared to the general population. While about 10% of people worldwide are left-handed, autism cases were 3.5 times more likely to exhibit non-right-handedness than control groups.

Even conditions like dyslexia and stuttering showed significantly higher rates of left-handedness.

“Language, like handedness, has a very one-sided location in the brain, so it stands to reason that the development of both and their disorders could be linked,” says lead researcher Julian Packheiser from Ruhr University Bochum, in a statement.

By combining data from ten previous meta-analyses, representing 402 datasets, researchers identified patterns across different diagnoses that had previously remained hidden when studying disorders in isolation.

Mixed-handedness – where individuals use different hands for different tasks without a strong preference – showed even higher rates in clinical populations than left-handedness itself, with 1.63 times higher odds compared to 1.34 for left-handedness.

Early Hand Preferences Plays a Key Role

Study authors identified three factors that consistently predicted higher rates of unusual handedness: neurodevelopmental conditions, disorders with early onset, and conditions affecting language function.

Hand preferences begin forming remarkably early – even before birth. Research shows that prenatal thumb sucking at 10 weeks gestation is highly predictive of hand preference later in life.

Disorders appearing earlier in life showed stronger associations with atypical handedness patterns. This observation backs growing evidence that many conditions affecting brain development begin extremely early, with handedness potentially serving as a visible sign of atypical neural development.

Not All Mental Health Conditions Show the Link

Interestingly, not all psychiatric conditions showed elevated left-handedness rates. Depression, math learning disability (dyscalculia), and pedophilia showed no meaningful differences in handedness compared to control groups.

This selective pattern reinforces the argument that specific developmental processes – not just general psychological issues – connect to handedness.

While these findings may eventually influence how doctors assess neurodevelopmental conditions, the researchers caution against overinterpretation. The differences, though statistically significant, aren’t substantial enough to use handedness alone for diagnosis. Many left-handed people never develop mental health conditions, and many people with these conditions are right-handed.

Nevertheless, this research establishes a compelling connection between how our brains organize basic functions like hand preference and more complex developmental processes. When these processes are disrupted, both handedness and mental health may be affected.