The biopsychosocial model of health and illness is a framework developed by George L. Engel that states that interactions between biological, psychological, and social factors determine the cause, manifestation, and outcome of wellness and disease. Historically, popular theories like the nature versus nurture debate posited that any one of these factors was sufficient to change the course of development. The biopsychosocial model argues that any one factor is not sufficient; it is the interplay between people’s genetic makeup (biology), mental health and behavior (psychology), and social and cultural context that determine the course of their health-related outcomes.

Biological Influences on Health

Biological influences on health include an individual’s genetic makeup and history of physical trauma or infection. Many disorders have an inherited genetic vulnerability. The greatest single risk factor for developing schizophrenia, for example is having a first-degree relative with the disease (risk is 6.5%); more than 40% of monozygotic twins of those with schizophrenia are also affected. If one parent is affected the risk is about 13%; if both are affected the risk is nearly 50%.

It is clear that genetics have an important role in the development of schizophrenia, but equally clear is that there must be other factors at play. Certain non-biological (i.e., environmental) factors influence the expression of the disorder in those with a pre-existing genetic risk.

Psychological Influences on Health

The psychological component of the biopsychosocial model seeks to find a psychological foundation for a particular symptom or array of symptoms (e.g., impulsivity, irritability, overwhelming sadness, etc.). Individuals with a genetic vulnerability may be more likely to display negative thinking that puts them at risk for depression; alternatively, psychological factors may exacerbate a biological predisposition by putting a genetically vulnerable person at risk for other risk behaviors. For example, depression on its own may not cause liver problems, but a person with depression may be more likely to abuse alcohol, and, therefore, develop liver damage. Increased risk-taking leads to an increased likelihood of disease.

Social Influences on Health

Social factors include socioeconomic status, culture, technology, and religion. For instance, losing one’s job or ending a romantic relationship may place one at risk of stress and illness. Such life events may predispose an individual to developing depression, which may, in turn, contribute to physical health problems. The impact of social factors is widely recognized in mental disorders like anorexia nervosa (a disorder characterized by excessive and purposeful weight loss despite evidence of low body weight). The fashion industry and the media promote an unhealthy standard of beauty that emphasizes thinness over health. This exerts social pressure to attain this “ideal” body image despite the obvious health risks.

Cultural Factors

Also included in the social domain are cultural factors. For instance, differences in the circumstances, expectations, and belief systems of different cultural groups contribute to different prevalence rates and symptom expression of disorders. For example, anorexia is less common in non-western cultures because they put less emphasis on thinness in women.

Culture can vary across a small geographic range, such as from lower-income to higher-income areas, and rates of disease and illness differ across these communities accordingly. Culture can even change biology, as research on epigenetics is beginning to show. Specifically, research on epigenetics suggests that the environment can actually alter an individual’s genetic makeup. For instance, research shows that individuals exposed to over-crowding and poverty are more at risk for developing depression with actual genetic mutations forming over only a single generation.

Application of the Biopsychosocial Model

The biopsychosocial model states that the workings of the body, mind, and environment all affect each other. According to this model, none of these factors in isolation is sufficient to lead definitively to health or illness—it is the deep interrelation of all three components that leads to a given outcome.

Health promotion must address all three factors, as a growing body of empirical literature suggests that it is the combination of health status, perceptions of health, and sociocultural barriers to accessing health care that influence the likelihood of a patient engaging in health-promoting behaviors, like taking medication, proper diet or nutrition, and engaging in physical activity.