Suicidal behavior can be viewed as a poor response to stress. Our reaction to stress is not only dependent on psychological variables, but our physiology (body makeup) also determines, in part, how we cope with stressful situations.
Specific Temperament Types Have an Increased Risk of Suicide
Personality is the relatively stable set of characteristics (called traits) that people display over time and across situations. Personality is composed of learned characteristics and genetically-based individual differences in attention, arousal, and reactivity to new or novel situations (called temperament).
Research suggests that suicidal adults and adolescents tend to display characteristic temperaments. The first is referred to as "depressive/withdrawn", "negativistic/avoidant", or "high in neuroticism". Individuals with the negativistic/avoidant temperament type show high levels of negative mood, have difficulty controlling their moods (particularly negative ones) and tend to "overreact" to daily stressors. As a result, these individuals are more likely to develop depression and anxiety disorders, and often commit suicide as a result. In addition, people with this temperament type often have histories of being abused or developing inadequate relationships with caregivers.
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Other people who commit suicide have an "impulsive/aggressive" (sometimes called the "negativistic/avoidant/antisocial") temperament. These individuals also have difficulty controlling their emotions, particularly anger, and are more likely than the individuals described above to commit suicide in the absence of a mood disorder like depression or anxiety. People with this temperament type are often diagnosed with antisocial personality disorder (a long-standing pattern of a disregard for other people's rights, breaking laws, deceitfulness, irritability and aggressiveness, reckless disregard for safety of self or others, consistent irresponsibility), or show some antisocial behaviors. "Impulsive/aggressive" people are sensation seekers, so they often engage in risky behavior, make poor and/or snap judgments, and abuse alcohol and/or other substances. Children with this temperament type often have histories of abuse (particularly sexual abuse).
Research suggests that someone's temperament type is related to genes that control the regulation of the neurotransmitters (chemical messengers in the brain and nervous system) norepinephrine and serotonin (substances that influence mood regulation). Temperament is also influenced by the environment and can affect someone's ability to cope with stress (so, for example, individuals with the temperament types described above would likely have poor coping skills and subsequent ability to deal with stress). In addition, very early on, someone's temperament influences the responses they receive from their caregivers. Difficult and highly irritable infants are not fun to be around, and they often trigger negative responses from caregivers. Difficult children may also experience negative reactions from peers, which then increases their risk for developing mental disorders. In turn, youth with psychological problems or psychiatric disorders have a greater risk of being exposed to stressful events related to these disorders, which then influences personality development and so on.
An Individual's Genetic Makeup Can Influence Suicide Risk
Research suggests that genetic factors are highly related to a particular person's risk for committing suicide. Suicide "runs " in families; the offspring of suicide attempters and completers are much more likely to engage suicidal behavior themselves. In addition, there are high suicide rates among adopted children whose biological families have elevated rates of suicide. Research with twins also supports a genetic link to suicide; if a monozygotic (i.e., genetically identical) twin attempted suicide, his/her co-twin has a 17.5-fold increased risk of having made an attempt as well. Genetic data about suicide has also been collected on concordance rates (i.e., the presence of the same trait in both members of a pair of twins). There is a higher concordance rate for suicide among monozygotic than dizygotic twins (11.3% vs. 1.8%). In other words, if an identical twin commits suicide, the co-twin has an 11.3-fold increased risk of committing suicide as well.
It is not exactly clear which genes are related to suicide. However, many researchers suggest that there is not a specific gene (or set of genes) that are increasing someone's suicide risk per se. Instead, what is being transmitted is a likelihood of developing specific types of mental illness that increase the risk of committing suicide (e.g., depression), or a specific personality type (e.g., impulsive/aggressive temperament). Others suggest that the genetic transmission of problems in the body's stress response systems (e.g., the HPA axis described below) or problems in the ability to control mood and impulsive behavior are likely culprits.
Neurological and Neurochemical Differences Increase Suicide Risk
The hypothalamic-pituitary-adrenal (HPA) axis (a system tying together the hypothalamus and the pituitary gland in the brain with the adrenal glands near the kidneys) controls our body's responses to actual, anticipated, or perceived harm. In addition, the HPA axis regulates our ability to adapt to stressors over time. Dysregulation of the HPA axis, which, in susceptible people, can develop following traumatic events or chronic stress, has been linked to severe depression, severe anxiety disorders (particularly PTSD), and suicidal behavior.
In response to stress, the HPA axis produces glucose, cortisol, and steroids. Each of these chemicals prepares our body for the famous "fight (i.e., confronting a stressor) or flight" (i.e., running away from a stressor) response by increasing blood and oxygen flow to the muscles, increasing heart rate, dilating pupils, enhancing the immune response, and increasing alertness. However, the body response initiated by the HPA axis cannot be sustained for long periods of time without leading to illness. Autopsy studies show that people who committed suicide have elevated cortisol levels and enlarged adrenal glands, suggesting that their bodies were experiencing extreme stress.
Exactly how the HPA axis influences suicidal behavior is not yet clear. Some researchers suggest that increased cortisol levels affect the mood-regulating neurotransmitter serotonin, making it difficult for serotonin to get to brain and nervous system receptors (i.e., neurochemical "catchers" that, when stimulated, can create a response). Both suicide attemptors and individuals who died from suicide have shown low serotonin levels (or poor ability to receive serotonin) in the brain stem and cerebrospinal fluid. In addition to regulating mood, serotonin seems to help inhibit impulsive behvaiors. Someone with a malfunctioning serotonin system may be more likely to engage in suicidal and other potentially harmful impulsive acts.
Suicidal people also seem to have lower levels of norepinephrine (also called epinephrine or adrenaline) in the part of the brain called the locus ceruleus. Norepinephrine is a chemical messenger that affects the central nervous system and the bloodstream. When you are confronted with danger, epinephrine is released into the bloodstream, increasing your heart rate and blood pressure, readying you for action.