Bipolar disorder is a mental health condition marked by distinct, intense shifts in mood, energy, and activity levels. These periods, known as mood episodes, can range from elevated or irritable states (mania or hypomania) to profoundly sad or hopeless feelings (depression). Individuals with bipolar disorder typically experience periods of stable mood between these episodes. These shifts last for days to weeks and significantly affect daily functioning, relationships, and ability to work or attend school.
Genetic and Brain Factors
A strong genetic component is associated with bipolar disorder, with 80% to 90% of individuals having a family member with either bipolar disorder or depression. The inheritance pattern is complex, involving multiple genes, each contributing a small amount to the overall risk rather than a single “bipolar gene.” A genetic predisposition increases risk but does not guarantee development.
Beyond genetics, differences in brain structure and function are observed in individuals with bipolar disorder. Neurotransmitters, which are chemical messengers in the brain, are involved. Imbalances in monoamines like dopamine, serotonin, and norepinephrine have been consistently linked to mood disorders, including bipolar disorder. These chemicals influence sleep, wakefulness, eating, and mood regulation.
Brain imaging studies show that individuals with bipolar disorder may have abnormalities in neural circuits that process emotions, regulate mood, and manage reward. Alterations in serotonin pathways and dopamine dysregulation are thought to contribute to mood disorders.
Life Events and Environment
Significant life stressors and traumatic experiences can contribute to bipolar disorder, especially in genetically predisposed individuals. These environmental influences interact with biological vulnerability, increasing the likelihood of symptoms. Examples include the loss of a loved one, severe financial difficulties, or experiences of abuse or neglect.
Childhood trauma, such as physical, emotional, or sexual abuse, or neglect, has been consistently linked to more severe psychopathology in adolescents with bipolar disorder. These adverse experiences can affect an individual’s ability to manage emotions and may lead to a more challenging course of the illness. Even positive life events or goal attainment can sometimes precede manic episodes.
Substance use is also a contributing factor and can significantly influence the course of bipolar disorder. Nearly 60% of individuals with bipolar disorder experience a co-occurring substance use disorder, with alcohol being the most commonly abused substance. While substance use alone does not cause bipolar disorder, it can trigger mood episodes in vulnerable individuals and may lead to an earlier onset, particularly if it begins in adolescence.
Other Health Conditions and Life Stages
Certain co-occurring physical and mental health conditions can heighten the risk for bipolar disorder or complicate its diagnosis. For example, anxiety disorders and Attention-Deficit/Hyperactivity Disorder (ADHD) are frequently found in individuals with bipolar I disorder. These conditions may indicate a broader vulnerability or shared biological pathways.
Thyroid conditions, such as hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), have also been linked to mental health issues, including bipolar disorder. An imbalance in thyroid hormones can disrupt neurotransmitters like serotonin and norepinephrine, which are involved in mood regulation. Hyperthyroidism symptoms, such as restlessness and irritability, can mimic mania, while hypothyroidism symptoms, like fatigue and sadness, can resemble depression.
The typical age of onset for bipolar disorder is late adolescence to early adulthood, averaging around 25 years, though it can manifest earlier in childhood or as late as 40 years of age. This developmental stage is considered particularly vulnerable due to ongoing brain development, hormonal changes, and increased exposure to stress. Early-onset bipolar disorder, especially before age 18, is often associated with a more severe course, including more frequent recurrences and a higher likelihood of co-occurring anxiety and substance use disorders.
Risk Factors Versus Triggers
Understanding the distinction between risk factors and triggers is crucial. A risk factor is an underlying vulnerability that increases the likelihood of developing the disorder. Examples include a family history of bipolar disorder, specific genetic predispositions, or early childhood trauma.
In contrast, a trigger is an event or circumstance that can precipitate a mood episode (either manic, hypomanic, or depressive) in someone who already has bipolar disorder or is highly susceptible. Triggers do not cause the disorder itself but can initiate symptoms. Common triggers include significant stressful life events, disruptions in sleep patterns, or the use of certain substances like alcohol or recreational drugs.
Having one or more risk factors does not guarantee developing bipolar disorder. Many people with genetic predispositions or who experience stressful life events never develop the condition. Instead, it is often a complex interplay of multiple risk factors that contribute to the onset of bipolar disorder.