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Becoming Suicidal: Biological Contributions

Natalie Staats Reiss, Ph.D., and Mark Dombeck, Ph.D.

DNA moleculeSuicidal behavior can be viewed as a poor response to stress. Our reaction to stress is affected by psychological variables. However, our physiology (body makeup) also, in part, affects how we cope with stressful situations.

Specific Temperament Types Have an Increased Risk of Suicide

Personality is the relatively stable set of characteristics that people display over time and across situations. These characteristics are called traits. Personality is made up of learned characteristics and genetically-based individual differences. These differences are in attention, arousal, and reactivity to new or different. This is known as temperament.

Research suggests that suicidal adults and adolescents tend to display certain temperaments. The first is referred to as "depressive/withdrawn", "negativistic/avoidant", or "high in neuroticism". Individuals with this temperament type show high levels of negative mood. They 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.

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. They are more likely than the individuals described above to commit suicide even without having a mood disorder like depression or anxiety. People with this temperament type are often diagnosed with antisocial personality disorder. This is 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. If they are not diagnosed with antisocial personality disorder, they may show some antisocial behaviors. "Impulsive/aggressive" people are sensation seekers. 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 in the brain and nervous system.  These are chemical messengers called norepinephrine and serotonin. These substances influence control of our moods. Temperament is also influenced by the environment and can affect someone's ability to cope with stress. For example, people with the temperament types described above would likely have poor coping skills and abilities to deal with stress. In addition, very early on, someone's temperament influences the reactions that they receive from their caregivers. Difficult and highly irritable infants are not fun to be around. They often trigger negative responses from caregivers. Difficult children may also experience negative reactions from peers, which then increases their risk for developing mental conditions.  Teens with psychological problems or mental health conditions have a greater risk of being exposed to stressful events related to these conditions, which then influences personality development.

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 an identical twin attempted suicide, his/her co-twin has a 17.5% increased risk of having made an attempt as well. If an identical twin commits suicide, the co-twin has an 11.3% 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. Instead, what is being transmitted is a likelihood of developing specific types of mental illness that increase the risk of committing suicide. For example, 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 is a system tying together the hypothalamus and the pituitary gland in the brain with the adrenal glands near the kidneys. It controls our body's responses to actual, anticipated, or perceived harm. In addition, the HPA axis controls our ability to adapt to stressors over time. Dysregulation of the HPA axis in vulnerable people can lead them to develop severe depression, severe anxiety disorders (particularly PTSD), and suicidal behavior following traumatic events or chronic stress.

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. They increase blood and oxygen flow to the muscles, increase heart rate, dilate pupils, enhancing the immune response, and increase alertness. However, this body response 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. This suggests 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. The levels may make it difficult for serotonin to get to brain and nervous system receptors. These are the neurochemical "catchers" that, when stimulated, can create a response in the body. Both suicide attempters 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 behaviors. 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. This increases your heart rate and blood pressure, readying your body for action.