Illiteracy linked to schizophrenia risk

By Mark Cowen

The risk for schizophrenia is significantly higher among illiterate than literate individuals in China, particularly among younger age groups, results from a population-based study show.

Indeed, Xiaoying Zheng (Peking University, China) and team found that illiterate people aged less than 40 years were more than twice as likely to develop schizophrenia as their literate peers.

"Both social selection and social cause processes may have operated in the association," comment the researchers. "Our study has implications for the role of social adversity in etiology of schizophrenia."

The findings come from a study of data on 1,909,205 individuals, aged 18 years or older, from the Second China National Sample Survey on Disability in 2006, of whom 7628 reported a diagnosis of schizophrenia.

Overall, 15.3% of the study population was illiterate, as ascertained through face-to-face interviews.

The researchers found that the prevalence of schizophrenia among illiterate individuals aged 18-29, 30-39, 40-49, 50-59, and 60 years or older was 1.64%, 1.51%, 1.07%, 0.88%, and 0.50%, respectively, compared with corresponding rates of 0.22%, 0.37%, 0.39%, 0.42%, and 0.29% among literate individuals.

After accounting for age, gender, marital status, location of residence, and household income, the team found that illiterate people were significantly more likely to develop schizophrenia than their literate counterparts, with a stronger association among those aged less than 40 years (odds ratio [OR]=2.08) than among older individuals (OR=1.34).

Further analysis that controlled for environment and genetic risk in more than 26,000 sibling sets aged less than 40 years revealed that illiterate siblings were 2.8 times more likely to develop schizophrenia than literate siblings from the same family.

"The current study found a strong association between illiteracy and schizophrenia among Chinese people less than 40 years old," conclude Zheng and team in Social Psychiatry and Psychiatric Epidemiology.

They add: "Future studies on the association between social environment and risk of schizophrenia as well as mechanisms underlying the association are necessary."

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