What is the epidemiology of schizophrenia?

Epidemiology of Schizophrenia

Schizophrenia affects approximately 0.7% of the global population during their lifetime, with 0.32% of the population affected at any given time, representing a significant worldwide health burden with substantial mortality and morbidity implications. 1, 2

Prevalence and Incidence

• The lifetime prevalence of schizophrenia is approximately 0.7%, according to the American Psychiatric Association's most recent authoritative estimate 2
• From 1990 to 2019, the raw global prevalence of schizophrenia increased by 65% (from 14.2 to 23.6 million cases), while age-standardized estimates remained relatively stable 3
• Schizophrenia incidence shows a bimodal distribution in women, with peaks at ages 20-29 and at menopausal age (44-49 years), while in men there is a single steep peak between ages 15-25 4
• Despite differences in age of onset, the lifetime risk appears to be similar for both sexes 4
• Global incidence increased by 37% (from 941,000 to 1.3 million new cases) between 1990 and 2019 3

Geographic and Demographic Variations

• Significant regional differences in prevalence exist due to variations in urbanicity and immigration patterns 5
• In countries with high socio-demographic index (SDI), both prevalence and disability-adjusted life years (DALYs) have increased over time 3
• In countries with low SDI, age-standardized incidence has decreased while DALYs have remained stable, suggesting potential underdetection in these regions 3
• No population-based studies on schizophrenia epidemiology have been conducted in low- and middle-income countries, where health problems related to schizophrenia may be more pronounced 1

Sex Differences

• The male-to-female ratio of schizophrenia burden has remained stable at approximately 1.1 over the past 30 years 3
• This ratio changes across the lifespan, with prevalence higher in males at younger ages but higher in females after age 65 3
• The lower incidence in premenopausal women is attributed to the protective effect of estrogen on dopamine receptors, which is counteracted by high genetic familial load 4

Mortality and Morbidity

• Schizophrenia is associated with significantly increased mortality, with standardized mortality ratios 2-4 times higher than the general population 2
• Approximately 4-10% of individuals with schizophrenia die by suicide, with rates highest among males early in the course of the disorder 2
• Schizophrenia ranks among the top 20 causes of disability worldwide 2
• The global burden of schizophrenia, measured in DALYs, increased by 65% (from 9.1 to 15.1 million) between 1990 and 2019 3

Special Populations: Pregnant Women with Schizophrenia

• Women with schizophrenia represent a particularly vulnerable population during pregnancy and childbirth 1
• Pregnancies in women with schizophrenia are associated with significantly increased risks of:
  • Gestational diabetes (OR 2.35) 1
  • Pre-eclampsia/eclampsia (OR 1.85) 1
  • Antepartum hemorrhage (OR 2.28) 1
  • Preterm and very preterm delivery (OR 1.79 and 2.31, respectively) 1
  • Stillbirths (OR 2.06) 1
  • Infant mortality (OR 2.33) 1
• These findings highlight the need for specialized perinatal care for this population 1

Clinical Course and Symptoms

• Most schizophrenia onsets are preceded by a prodromal stage extending over several years, which produces the maximum social consequences 4
• In the long-term illness course, the number of psychotic relapse episodes ranges from 0 to 29, with a mean of 3 4
• Positive symptoms produce the highest number of relapses but have the shortest duration of exacerbations (mean of two months) 4
• Depressive and negative symptom exacerbations last nearly six months on average 4
• Following the first illness episode, symptom scores decline sharply, reaching a plateau five years after first admission 4
• Depression is the most frequent type of symptom in the long-term course 4

Etiology and Pathophysiology

• Schizophrenia has a heterogeneous genetic and neurobiological background that influences early brain development 5
• The disorder involves subtle pathological changes in specific neural cell populations and cell-cell communication rather than gross brain pathology 5
• Neuroimaging studies have shown functionally abnormal information processing in patients with first-episode and chronic schizophrenia 5
• Recent research points to a central role for several neurotransmitters, including dopamine, glutamate, and serotonin, which may interface with neurodevelopmental defects reflecting disease-related genetic aberrations 6

Clinical Implications

• Early identification of individuals at risk and those in early phases of the disorder is crucial, as schizophrenia typically starts many years before diagnosis 5
• Current pharmacological treatments primarily target dopamine D2 receptors, which helps with positive symptoms but contributes to adverse effects 7
• Psychosocial interventions such as cognitive-behavioral therapy, cognitive remediation, and supported education and employment add treatment value but are inconsistently applied 5
• The complex presentation and multifactorial etiology of schizophrenia highlight the need for novel treatment approaches targeting specific neural circuits 7