The Diathesis-Stress Model of Mental Illness

 This is part of my assignment for the subject "Stress and Health" MA Psychology 2nd Year.

The Diathesis-Stress Model of Mental Illness

The Diathesis-Stress Model of mental illness is used to explain the pathogenesis of mental illness (cause of mental illness or etiology). It is one of the most widely accepted theories for explaining the origin of mental disorders. It proposes that psychological disorders arise from the interaction between a person’s predispositional vulnerability (diathesis) and environmental stressors. Neither vulnerability nor stress alone is sufficient; rather, it is their combination that triggers illness. The term Diathesis comes from Greek word meaning predisposition or arrangement. 

American Psychologist Paul Meehl, in his paper in 1962, applied this model to explain the origins of schizophrenia suggesting that a genetic vulnerability (schizotaxia) combined with stress could lead to the disorder. Since then, it has been applied to other mental disorders also like depression, anxiety, eating disorders, PTSD, suicidal behaviour etc. The model was further developed by Manfred Bleuler and David Rosenthal in late 1960s in the context of schizophrenia risk factors.

Core Concepts of the Model

          The diathesis-stress model is a biopsychosocial framework that posits that a disorder develops from a combination of Diathesis and Stress as enumerated:

• Diathesis (Predisposition):
• Genetic vulnerability (e.g., family history of schizophrenia or depression).
• Personality traits (e.g., neuroticism, perfectionism).
• Early childhood trauma or insecure attachment.
• Stress (Environmental Triggers):
• Life events such as bereavement, unemployment, or academic failure.
• Social pressures like stigma, poverty, or gender discrimination.
• Cultural expectations and family conflicts.
• Interaction:
• A person with high vulnerability may develop illness under mild stress.
• A person with low vulnerability may remain resilient even under severe stress.

This dynamic interaction explains why not everyone exposed to stress develops mental illness, and why some individuals with genetic predispositions remain healthy if stress is minimized.

CASE STUDIES

The Diathesis-Stress Model is not only a theoretical construct but also a lens through which the lives of well-known individuals can be understood. Examining well known figures such as Sylvia Plath, Princess Diana, and Parveen Babi reveals how predispositional vulnerabilities interacted with environmental stressors to produce mental illness. These cases highlight the universality of the model across cultures, while also underscoring the importance of contextual factors.

Sylvia Plath

Sylvia Plath (1932-1963), the celebrated American poet and author, wrote about her mental health struggles, female oppression, suicidal ideation-at a time when such topics were rarely discussed in open. Her famous novel, “The Bell Jar” is a semi-autobiographical, depicting a young woman’s descent into mental illness and the pressures of societal expectations. Her life narrated through her poetry and novel fits with the diathesis-stress model of illness. Let us have a look:

• Diathesis: Plath’s predisposition included a family history of depression, perfectionist personality traits, and unresolved trauma from her father’s death.
• Stress: Academic pressures, marital discord, and social isolation acted as triggers.
• Outcome: These factors culminated in severe depressive episodes and ultimately suicide. Plath’s case demonstrates how genetic vulnerability combined with situational stress can overwhelm coping mechanisms, leading to tragic outcomes.

Princess Diana

Princess Diana’s life illustrates the role of social and cultural stressors in mental illness.

• Diathesis: Diana’s fragile self-esteem and childhood instability (parental divorce, emotional neglect) created vulnerability.
• Stress: Constant media scrutiny, marital discord, and the rigid expectations of royal life intensified her struggles.
• Outcome: She developed bulimia nervosa and depressive symptoms, openly acknowledging her battles with mental health. Her case shows how environmental pressures, particularly public scrutiny, can exacerbate predispositions, leading to chronic psychological distress.

Parveen Babi

Parveen Babi, one of Bollywood’s most iconic actresses of 1970s era, became schizophrenic due to existing vulnerabilities and stress of film world.

• Diathesis: Babi had a genetic predisposition to schizophrenia or schizoaffective disorder, compounded by her sensitive artistic temperament.
• Stress: The intense pressures of fame, broken relationships, and social stigma around mental illness in India acted as triggers.
• Outcome: She experienced chronic psychotic symptoms, paranoia, and eventual social withdrawal, living in isolation until her death. Her case highlights how stigma and lack of sustained treatment can worsen outcomes, especially in societies where mental illness is poorly understood.

Comparative Analysis

These three cases reveal striking parallels:

• Each of the three individuals had predispositional vulnerabilities rooted in genetics, personality, or early trauma.
• Each faced intense stressors—academic, relational, societal, or cultural—that interacted with their vulnerabilities.
• The outcomes ranged from mood disorders and eating disorders to psychosis and suicide, underscoring the model’s explanatory power.

The key assumption is that neither the diathesis or the stressors alone is sufficient to cause the disorder, rather, it is their interaction that leads to the onset of the condition.

CUP AND WATER ANALOGY

     The cup or bucket and water analogy can be used to explain the model in psychology. The cup size denotes the diathesis or preexisting vulnerability. A large cup would indicate that the person has large capacity to handle stress or he is less vulnerable. A small cup indicates that the person is more vulnerable or his capability to handle stress is low. Water represents Stress which could be academic pressures, family problems, financial worries, work related pressures or environmental factors. Now coming to interaction part. Mental health problems occur when the cup overflows. If the stress (water) becomes too much for the size of the cup, it overflows, symbolizing the onset of a mental disorder or psychological distress. To summarise, both vulnerability (the size of the cup) and stress (water) interact. A person with high vulnerability needs less stress to overflow: a person with low vulnerability can tolerate more stress before overflow.

CONCLUSION AND INFERENCES

     The Diathesis-stress model has been instrumental in checking the over dominance of medical model which believed that mental disorder is caused by an imbalance in brain chemistry which supported the goals of pharmaceutical industry. Though there is very little evidence to support this theory. The limitations of the medical-model can be explained by taking the case of depression. As per the medical model depression is caused by deficit of serotonin. Now if we carry out a study of depressed or nondepressed people we will find that this theory falls flat as there could be depressed people with normal level of serotonin and vice-versa. Only Diathesis-stress model resolves this ambiguity. It lays equal importance top the Nature and nurture when it comes to development of mental disorders.

     Another interesting fall out of this model is that ABNORMALITY ITSELF IS NOT INHERITED, BUT A PREDISPOSITION (VULNERABILITY) TO DEVELOP THE ILLNESS IS INHERITED. This would mean that a person with a genetic history of mental disorder will not get the disease only on basis of genetics but only if he is faced with stressors. Thus, in such cases it will be a good approach if emphasis is paid to the environmental factors. The approach brings back the psychologists and social workers within the scope of treatment of mental disorders.

     This leads to yet interesting conjecture. Is there really any such gene or chromosome which is inherited which passes the disease? Research till now has not been able to identify any such evidence or isolate any such gene.

     Let us listen to Dr. William Glasser, an American psychiatrist with more than 40 years of experience in the field, who developed Reality Therapy and Choice Theory, which emphasised personal responsibility and the idea that all behaviour is chosen. He questioned the medical model of mental illness, opposing heavy reliance on psychiatric drugs. Few words from his book, “Psychiatry can be Hazardous to your Mental Health” follows:

     “The medical approach to mental distress is based on unproven hypothesis, in particular the theory that the fundamental cause of mental distress is biological, either a biochemical imbalance or , a genetic defect or both. Psychiatry has convinced itself and the general public that this hypothesis is not only a hypothesis but a proven fact”

     “Decades of intensive psychiatric research have failed to establish a biological cause for any psychiatric condition. The lack of biological evidence is confirmed by the extraordinary fact that not a single psychiatric diagnosis can be confirmed by the biochemical, radiological, or other laboratory test. I know of no other medical speciality where vast number of people are treated on the presumption of a biochemical abnormality. The medical professions reliance on biology as the determining factor for psychiatric disorder is founded upon faith rather than true scientific research. It seems to me that doctors shoot in the dark far more than the public realises”.

Birender Singh Yadav

244/PAP/011

Stress and Health