Mental disorders usually are caused by a combination of genetic and biological factors (nature) and environmental factors (nurture). Substance use and other medical conditions also can play a role in mental health problems. Although it is difficult to separate the role of factors in an individual presentation of mental illness, it is important to understand how these factors independently affect mental functioning so prevention and interventions can be implemented.
Genetic / Biological Causes
Many mental disorders have a genetic component, meaning a predisposition or vulnerability to a particular illness can be passed down through family. According to the 2000 Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), individuals with first-degree relatives suffering from schizophrenia are at 10 times greater risk for getting the illness themselves compared to the general population. Major depressive episodes are between one and a half and three times more common in individuals with first-degree relatives who also suffer from major depression.
In addition, alcohol dependence, anxiety disorders and attention deficit/hyperactivity disorder (ADHD) have been found at increased incidences among those with first-degree biological family members with major depression. Bipolar disorders have a strong genetic factor; increased incidence of either bipolar I or bipolar II disorders have been found to be between 4 and 24 percent in those with a first-degree biological relative with the disorder. These individuals also show an increased likelihood (between 1 and 5 percent) of developing major depressive disorder. Panic disorder also carries a strong genetic link. According to the DSM-IV-TR, those with first-degree biological relatives with panic disorder are 8 to 20 percent more likely to get the disorder themselves.
Environmental Causes
Environmental conditions also play a large role in the development of, or resilience to, mental illness. Many parents struggle to provide consistent, patient and nurturing environments for their children. Inconsistency, neglect and abuse on the part of the parent (lack of appropriate food, vitamins or doctor visits, for example) can affect the child's development as well as affect his ability to construct a healthy model of interpersonal relationships and social behavior.
Other environmental factors outside the family also can affect mental health. For example, toxins such as lead in paint have been linked to a number of developmental and cognitive deficits, and certain foods have been linked to hyperactivity and ADHD symptoms. Environmental disasters such as hurricanes or earthquakes, or other dangerous situations such as a school shooting or being mugged, can lead to symptoms of anxiety, post traumatic stress disorder (PTSD) and depression.
General Medical Conditions
Sometimes, symptoms of mental illness arise due to a physical change or medical condition. Traumatic brain injury can result in personality changes, although these changes are not always negative. Other medical conditions, such as diabetes also can affect mental health. If uncontrolled, blood sugar fluctuations in diabetics can cause significant fluctuations in mood, temper, impulse control and cognitive acuity.
Substance Use
Substance use and abuse is often comorbid with mental illness. It is often difficult to determine if substance use triggers underlying vulnerabilities for mental illness or if individuals are "self-medicating" a pre-existing mental illness, but the substances themselves can cause symptoms of mental illness. For example, individuals who use crack, cocaine or amphetamines can become paranoid and delusional secondary to their drug use or drug withdraw. Alcohol and barbiturates are "downers" and can cause symptoms of depression or anxiety. Certain prescription medications include side effects with potential mental illness symptoms such as hallucinations, thoughts of suicide, sleep disorders and anxiety.
References
- "Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision"; American Psychiatric Association; 2000
- Lead Action News: Health Impacts of Lead Poisoning
