The Interplay of Adversity: The Bidirectional Relationship Between Mental Health and Homelessness

Mental health disorders and homelessness, two under-studied conditions, carry serious public health, social, and economic costs. The urgency lies in the bidirectional relationship between these two conditions, where one can exacerbate the other. Individuals with mental health disorders are at a heightened risk of homelessness, and conversely, those experiencing homelessness are at an increased risk of developing mental health disorders.

While the public health and medical communities have started to focus more on mental health and substance use disorders, homelessness remains a condition that is not fully understood. There is a significant lack of knowledge about the prevalence of homelessness in our population. Moreover, very little is known about the prevalence of mental illness among those experiencing homelessness.

How are homelessness and mental health disorders related?

The relationship between mental health disorders and homelessness is bidirectional. Mental health disorders may lead to situations that result in homelessness, or homelessness may be a stressor contributing to the development or worsening of mental health disorder symptoms.

On an individual level, people with mental health disorders may experience challenges such as substance use, relationship conflicts, and traumatic experiences that can contribute to the risk of experiencing homelessness. At the socioeconomic level, factors such as poverty, lack of affordable housing, transitions from foster care or institutional settings, stigma, racism, and discrimination may further perpetuate homelessness for people with mental health disorders. Antisocial personality disorder, for example, shares common risk factors with homelessness, such as poverty and early life trauma.

Homelessness, in turn, is associated with poor social and economic conditions and significant health inequalities, which can contribute to or exacerbate mental health and substance use disorders. Furthermore, the stressors related to being unhoused can contribute to the development

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of mental health disorders.

Given the barriers associated with quantifying homelessness, little is known about the prevalence of mental health disorders among those experiencing homelessness.

What did this study do?

This study is the first systematic review and meta-analysis to examine the relationship between mental health disorders and homelessness on a global scale. In this study, researchers reviewed and synthesized the existing literature detailing the factors associated with mental health disorders among adults aged 18 or older experiencing homelessness. This study had two aims:

1. Develop a better understanding of the prevalence of mental health disorders among people experiencing homelessness.
2. Estimate the pooled prevalence of any mental health disorder and specific mental health disorders among people experiencing homelessness.

The researchers defined homelessness as living in a shelter or a place not intended as a permanent dwelling. Patients must have been diagnosed with a mental health disorder based on DSM, ICD, or a similar diagnostic instrument to be included in the study.

The primary outcome of this study was the current prevalence of any mental health disorder, including substance use disorders. Secondary outcomes included:

• The lifetime prevalence of any diagnosed mental health disorder.
• Sex-specific prevalence of any mental health disorder.
• The prevalence of individual mental health disorder diagnostic categories.

Of note, the researchers did not include studies on suicide, self-harm, and tobacco use.

What did this study find?

The researchers included 85 studies, comprising 48 414 participants, in their final analysis. Most studies were conducted in high-income countries. The current prevalence of mental health disorders among people experiencing homelessness was 67%. The lifetime prevalence of mental health disorders was 77%. The lifetime prevalence of mental health disorders was significantly higher among men than women.

By pooling and analyzing the results of all included studies, the researchers could estimate the prevalence of specific mental health disorders among the participants. The disorders with the highest estimated prevalence were:

1. Substance use disorders (44%)
2. Antisocial personality disorder (26%)
3. Major depression (19%)
4. Bipolar disorder (8%)
5. Schizophrenia (7%)

Concerningly, the researchers found that the prevalence of mental health disorders among people experiencing homelessness was higher in recent studies compared to those published in earlier years. This suggests that the prevalence of mental health disorders is increasing among the homeless population. The researchers hypothesized that this could be due to persistent factors such as a lack of affordable housing, difficulty accessing mental health care, low income, or challenges reintegrating after mental health treatment.

What are the implications of this study?

Experiencing homelessness is a significant risk factor for developing or worsening mental health disorders. In turn, having a current or lifetime mental health condition increases the risk that someone will experience homelessness at some point throughout their lifetime. Of significant concern, rates of mental illness among those experiencing homelessness appear to have increased in recent years.

Rates of mental illness among those experiencing homelessness are dramatically higher than among the general population. For example, 12-15% of the general population are currently diagnosed with substance use disorders, compared to 44% of the homeless population. Similarly, the prevalence of depression in the general population is 5% versus 19% in the homeless population.

Both homelessness and mental health disorders are severe, debilitating conditions that require more social, economic, and public health investment. Specific interventions are needed to support the mental health needs of this population, including close coordination of mental health, social, and housing services and policies to support people experiencing homelessness with mental disorders. Such interventions could include housing first and critical time strategies or assertive community treatment plans. Sex-specific interventions may also be needed to address the significantly higher prevalence of mental health disorders among men experiencing homelessness.

What are the key takeaways?

• There is a bidirectional relationship between mental health disorders and homelessness.
• 67% of people who experience homelessness have a current mental health disorder.
• The most common mental health disorders among people experiencing homelessness are substance use disorders, antisocial personality disorder, and major depression.
• Rates of mental health disorders in the homeless population may be increasing.
• Specific interventions are needed that combine mental health, social, and housing services to support those experiencing homelessness and mental health disorders.

Reference

Barry R, Anderson J, Tran L, et al. Prevalence of Mental Health Disorders Among Individuals Experiencing Homelessness: A Systematic Review and Meta-Analysis. JAMA Psychiatry. 2024;81(7):691–699. doi:10.1001/jamapsychiatry.2024.0426