Schizophrenia is a chronic brain disorder that alters how an individual thinks, feels, and behaves. This condition can disrupt thought processes, perceptions, and emotional responses, affecting various aspects of life. This article explores the occurrence of schizophrenia across different populations and how its prevalence may have changed over time.
Global and Regional Occurrence
Schizophrenia affects approximately 24 million people globally, or about 1 in 300 individuals worldwide, according to the World Health Organization (WHO). This translates to a lifetime prevalence ranging from 0.3% to 0.7% of the general population. In the United States, prevalence estimates for schizophrenia and related psychotic disorders typically fall between 0.25% and 0.64%.
While the overall prevalence of schizophrenia is considered relatively consistent globally, some regional variations have been observed. For instance, a 2020 global trends report suggested that China, the Netherlands, and Australia had the highest age-adjusted rates of schizophrenia. A 2018 systematic review also found higher prevalence in East, South, and Southeast Asia, as well as Western Europe and high-income North America.
Despite regional differences, schizophrenia is a universally present disorder. For example, a 2000 WHO study found prevalence and incidence broadly similar worldwide, with age-standardized prevalence per 100,000 ranging from 343 in Africa to 544 in Japan and Oceania for men, and from 378 in Africa to 527 in Southeastern Europe for women. The disorder remains a global health concern.
Demographic Patterns
Schizophrenia exhibits distinct patterns across different demographic groups, particularly concerning age and gender. Symptoms most frequently emerge in late adolescence through the early thirties, with the average age of onset globally estimated between 25 and 27 years. It is uncommon for symptoms to appear in childhood or after age 45.
Gender differences exist in the age of onset; males typically experience symptoms earlier, between 21 and 25 years of age. Females, in contrast, generally show symptoms later, often between 25 and 30 years. While the overall lifetime prevalence is similar for males and females, males may be diagnosed slightly more often, with some studies suggesting a male-to-female ratio of 1.4:1. Clinical signs are generally less severe for women, and the disease course tends to be more challenging for men.
Researchers have not identified specific racial differences in schizophrenia occurrence. However, studies note a higher occurrence among immigrants compared to native-born individuals, a trend extending to second-generation immigrants. The precise reasons for this observation are not fully understood, but theories include potential overdiagnosis in immigrant populations and stress from relocating. Socioeconomic status is also a factor, with research indicating that early-onset schizophrenia is more common in males, associated with lower educational attainment, and higher unemployment rates.
Factors Influencing Occurrence
Schizophrenia’s development is not attributed to a single cause but to a complex interplay of factors. Genetic predisposition plays a significant role, as the condition tends to run in families. While no single gene is solely responsible, combinations of genes are thought to increase vulnerability. For instance, if one identical twin develops schizophrenia, the other has about a 1 in 2 chance of developing it, even if raised separately, compared to a 1 in 8 chance for non-identical twins. This suggests genetics contribute substantially but are not the only determinant.
Environmental and social factors also interact with genetic vulnerability. Prenatal complications, such as a birthing parent’s health during pregnancy, childbirth complications, or exposure to infections like toxoplasmosis, can increase the risk. Childhood trauma, including experiences like poverty or abuse, and social isolation are also considered potential environmental triggers. Living in an urban area and being born in winter are also risk factors.
Substance use, particularly cannabis, has been linked to an increased risk of developing schizophrenia in genetically susceptible individuals. Stressful life events, such as bereavement, job loss, or relationship endings, can also trigger a psychotic episode in those prone to the condition. These influences highlight that schizophrenia arises from a multifaceted interaction between inherited tendencies and external experiences.
Trends in Occurrence Over Time
Assessing long-term trends in schizophrenia prevalence is complex due to evolving diagnostic criteria and data collection methods. While some studies indicate relative stability in prevalence over recent decades, others suggest potential shifts. The Global Burden of Disease (GBD) Study reported an increase in the global prevalence of schizophrenia from 14.2 million in 1990 to 23.6 million in 2019, a rise of over 65%. Annual incidence also grew from 941,000 to 1.3 million, and disability-adjusted life years (DALYs) increased from 9.1 to 15.1 million during the same period.
This observed increase might be partly attributed to improved education about the disorder and a reduction in stigma, allowing mental health professionals to make more informed diagnoses. Despite the rise in incident cases and DALYs, the age-standardized incidence rate (ASIR) globally decreased slightly from 1990 to 2017, while the age-standardized death rate (ASDR) remained stable. The ASIR and DALYs were consistently higher for males than for females throughout this period.
These trends underscore the ongoing public health burden of schizophrenia. Although the ASDR has been stable for both males and females individually, the overall increase in the number of individuals living with schizophrenia suggests a need for continued monitoring and research into the factors influencing its occurrence across populations.