In the public perception, there is a strong association between mental disorders and high intelligence. Movies and books are filled with characters whose genius is linked to mental instability and illness. Rather than resist this romanticizing, geniuses have often encouraged the association. For instance, Edgar Allen Poe once said, “Men have called me mad, but the question is not yet settled whether madness is or is not the loftiest intelligence – whether all that is profound – does not spring from disease of thought.” This idea has dominated the public imagination so that few have considered the more mundane possibility that low IQ correlates with mental disorders. Dr. Karestan Koenen led a team of researchers from the Harvard School of Public Health to investigate this possibility. Her study appears this month in the American Journal of Psychiatry.

Dr. Koenen based her study on the idea of “cognitive reserve”, first coined in 1988 in the Annals of Neurology. In that seminal study, researchers found that subjects with more education and intelligence were able to stave off the negative effects of Alzheimer’s disease for longer. Dr. Koenen sought to find out whether this cognitive reserve could protect against a variety of other mental problems. To do so, she studied 1,037 subjects whose childhood IQs were measured in the Dunedin Multidisciplinary Health and Development Study.

Dr. Koenen followed the children from the Dunedin study, testing them for mental disorders from the DSM at ages 18, 21, 26, and 32. Lower childhood IQ correlated with adult depression, schizophrenia, and anxiety. Low IQ was also linked to a higher chance of having multiple disorders at once and of having more persistent depression. Higher IQ correlated with mania.