Monday, October 4, 2004 Posted: 3:28 PM EDT (1928 GMT)
CHICAGO, Illinois (Reuters) -- Schizophrenics born during the summer in the Northern Hemisphere tend to develop a more severe form of the mental illness than those born during the winter, a study said Monday.
An analysis of nearly 1,600 people with schizophrenia from six countries in that hemisphere found an association between June and July births and cases of "deficit" schizophrenia, which is characterized by an inability to experience pleasure, antisocial behavior and blunted speech.
Symptoms of this type of schizophrenia tend to worsen more quickly and become more severe.
Winter births were associated with non-deficit schizophrenia, which is characterized by hallucinations and incoherent and delusional thinking.
"Seasonal variations in infectious agents, sunlight exposure and vitamin D, and the availability of nutrients have been proposed as possible explanations for the seasonality of births in schizophrenia. "However, to date, no specific agent has been identified," wrote study author Erick Messias of Johns Hopkins University in Baltimore in The Archives of General Psychiatry.
Some 2 million Americans have schizophrenia, and the illness affects roughly 1 percent of the world's population. The disease usually shows up between the ages of 15 and 25.