Schizophrenia is a chronic and severe mental disorder that affects how a person thinks, feels, and behaves. The causes of schizophrenia are still not fully understood, but research suggests that a combination of genetics, brain chemistry, and environment contributes to development of the condition. Homelessness is associated with higher rates of mental illness, including schizophrenia. This raises the question of whether homelessness itself can cause schizophrenia to develop in someone predisposed to it.
What is Schizophrenia?
Schizophrenia is characterized by hallucinations, delusions, disorganized thinking and speech, and negative symptoms such as apathy and social withdrawal. Hallucinations involve seeing, hearing, or sensing things that are not actually present. Delusions are fixed false beliefs that are firmly held despite evidence to the contrary. Disorganized thinking makes it difficult for people with schizophrenia to concentrate, remember things, and complete tasks.
Schizophrenia typically first appears in the late teens to early 30s. The average age of onset is early to mid 20s for men and late 20s for women. It affects about 1% of the population at some point in their lives. Symptoms of schizophrenia fall into three broad categories:
– Positive symptoms – These include hallucinations, delusions, and disorganized thinking and speech. They reflect an excess or distortion of normal functions.
– Negative symptoms – These involve the loss or diminishment of normal emotions and behaviors. They include flat emotional expression, lack of motivation, reduced speech, and social withdrawal.
– Cognitive symptoms – These affect concentration, memory, and executive functioning skills involved in planning and decision making.
Schizophrenia is usually chronic, requiring lifelong management. With appropriate treatment, many people with schizophrenia can lead productive and fulfilling lives. Treatment typically involves medication combined with psychosocial support such as therapy and rehabilitation. Hospitalization may be necessary during acute psychotic episodes when people are at risk of harming themselves or others.
What Causes Schizophrenia?
The exact causes of schizophrenia are not known, but research suggests that a combination of genetic, environmental, and brain developmental factors are involved. These include:
– Genetics – Schizophrenia has a strong hereditary component. Having a close family member with schizophrenia increases risk. Many genes are believed to be involved, each contributing a small risk.
– Environmental exposures – Exposure to viruses, malnutrition before birth, problems during birth, and psychosocial factors such as childhood trauma and stress may play a role.
– Brain chemistry – An imbalance in neurotransmitters like dopamine and glutamate is thought to contribute to schizophrenia. The drug phencyclidine (PCP) can cause schizophrenia-like symptoms.
– Brain structure – Brain imaging studies show differences in the structure and function of certain brain regions in people with schizophrenia. This includes reduced gray matter volume in the frontal and temporal lobes.
However, many people with these risk factors do not develop schizophrenia. Likewise, many people diagnosed with schizophrenia have no family history or other risk factors. This suggests that environmental triggers and genetic susceptibilities interact in complex ways to cause schizophrenia.
Is Schizophrenia More Common in Homeless Populations?
Many studies conducted in the United States, Canada, Europe, and Australia have found higher rates of schizophrenia and other psychotic disorders among homeless people compared to the general population.
For example, a 2015 review of research on mental illness among homeless populations in Western countries found:
– 10-13% of homeless people have a psychotic disorder such as schizophrenia.
– 30-50% of homeless people have some form of mental illness.
In contrast, schizophrenia affects only around 1% of the general public. Mood disorders such as depression affect around 10% of the general public.
The high prevalence of schizophrenia among homeless arises in part because people with serious mental illness are at increased risk of becoming homeless. Contributing factors include poverty, unemployment, social isolation, limited access to health care, and substance abuse.
However, some evidence suggests that the stress and trauma of homelessness can also precipitate new cases of psychosis in vulnerable individuals. Let’s examine the evidence behind this theory.
Does Homelessness Directly Cause Schizophrenia?
There are several reasons why homelessness itself could potentially trigger the onset of schizophrenia:
Stress
Homelessness is an intensely stressful experience. The daily struggle for food, shelter, and safety compounded by social isolation almost invariably leads to psychological distress.
Stress is known to play a role in precipitating psychotic episodes in people already diagnosed with schizophrenia. High levels of long-term stress could also potentially unmask latent genetic vulnerabilities for psychosis.
Childhood Trauma
Many homeless people endured traumatic experiences in childhood, including physical or emotional abuse, neglect, and household dysfunction.
Childhood adversity is linked to increased risk of psychosis later in life. Trauma may act by sensitizing the body’s stress response system. Ongoing traumatization in homelessness could exacerbate these effects.
Substance Abuse
High rates of drug and alcohol abuse are seen among homeless populations. While sometimes used as a form of self-medication, substance abuse can exacerbate psychosis and symptoms of schizophrenia.
One study of homeless addicts in Boston found that 27% experienced drug-induced psychosis. Chronic substance abuse may lead to permanent changes in brain chemistry that increase psychosis risk.
Nutritional Deficiencies
Poor nutrition is common among the homeless. Deficiencies in vitamins and minerals such as niacin, vitamin B6, and zinc have all been implicated in some cases of schizophrenia. Lack of proper nutrition may compound genetic susceptibilities.
Traumatic Brain Injury
Homeless people experience high rates of head injury through assaults, accidents, and falls. Traumatic brain injury is a known risk factor for later development of psychotic disorders including schizophrenia.
Social Isolation
Loneliness and lack of social support systems are endemic among the homeless. Social isolation exacerbates many of the other stresses associated with homelessness. Some research indicates it could be an independent risk factor for schizophrenia.
Does Homelessness Directly Cause Schizophrenia? The Evidence
While homelessness is linked to higher rates of schizophrenia, there are differing views on whether it can directly cause schizophrenia in someone not previously experiencing psychosis. Here is a look at some key evidence:
Cross-Sectional Studies
Several studies have compared the current mental health status of homeless people versus non-homeless people matched for other schizophrenia risk factors such as age, gender, and socioeconomic status.
For example, a Canadian study published in 2001 matched 195 homeless men to 130 non-homeless men recruited through local health services and social programs. 14% of the homeless men had a diagnosis of schizophrenia versus only 3% of the housed men.
While suggestive, cross-sectional studies like this cannot prove homelessness causes schizophrenia, since the homeless participants may have already had emerging symptoms prior to becoming homeless.
Longitudinal Studies
Longitudinal studies that follow homeless individuals forward in time provide stronger evidence regarding causation.
In a 2004 American study, homeless men were recruited from shelters and assessed for symptoms of psychosis at baseline. After six months, 7% of those initially free of psychosis had developed schizophrenic or schizoaffective disorder. Higher levels of self-reported stress increased risk.
In another longitudinal study in Canada, 5% of homeless men developed new psychotic symptoms over a one-year period. Younger age, trauma history, and substance abuse were predictors of new psychosis onset.
Overall, longitudinal studies indicate that homelessness can precipitate new cases of schizophrenia in a minority subset of high-risk individuals.
Brain Imaging Studies
Brain scans show structural and functional brain differences in people with schizophrenia. A 2016 meta-analysis concluded that temporal lobe changes can be detected even prior to onset of psychosis.
If homelessness can directly cause schizophrenia, similar brain changes might be detectable in people after they become homeless. However, no imaging studies have yet investigated this.
Intervention Studies
Research testing whether interventions that improve housing stability reduce rates of new schizophrenia onset would provide the strongest evidence of causation. However, no such studies exist to date.
Conclusion
In summary, schizophrenia and other psychotic disorders are more prevalent among homeless populations compared to the general public. High rates arise in part because mental illness increases risk of becoming homeless. However, longitudinal studies also show that for a subset of vulnerable individuals, the stresses of homelessness can unmask latent genetic risks and precipitate new cases of schizophrenia. Childhood trauma, substance abuse, poor nutrition, and social isolation may act synergistically to trigger onset of psychosis after the initial loss of stable housing. At a biological level, chronic stress, trauma, and nutritional deficits may tip brain chemistry and neurodevelopment toward psychosis in those genetically predisposed. While homelessness does not directly cause schizophrenia by itself, it likely contributes by amplifying pre-existing susceptibilities in some people. Improving services and interventions to promote housing stability could potentially prevent some fraction of new schizophrenia cases. More research is needed to strengthen the evidence base and better quantify the risk attributable to homelessness itself. In the meantime, providing comprehensive mental health and social services to homeless populations remains imperative given their clear vulnerability to psychotic disorders.