What causes depression?
The causes of depression are not easily defined. When speaking of cause, it is typical to think in terms of infections of the lungs causing pneumonia or of cigarette smoking causing lung cancer. In actuality, most medical conditions cannot be so easily defined as having clearly linked causes. In fact, it took many years of statistical analysis before scientists could demonstrate a clear causal link between cigarette smoking and lung cancer. Even today, people argue, “My grandmother smoked her entire life and died at the ripe old age of 90 from natural causes. How can cigarettes possibly cause cancer?” The reality is that cigarette smoking is only one portion, albeit a big one, of the causal puzzle, that when pieced together leads to lung cancer. This is true of most diseases today. Instead, when physicians talk about cause, they are really talking about risk factors that influence the odds of developing a particular illness.
Depression, a complex illness, is more like an illness with multiple causes that influence the odds of someone developing it. Depression runs in families but is not 100% heritable. Depression may occur in someone with no family history for the illness. When considering the causes of depression, the odds are impacted by a variety of sources inside and outside of a person. This variety constitutes what is called the biopsychosocial model that is typically employed. In this model, consideration is given to biological, psychological, and social factors that may contribute to the onset of depression. This model influences most diseases of lifestyle. Look at, for instance, heart disease. Applying the biopsychosocial model to heart disease demonstrates biological risk factors of family history, the presence of high blood pressure and high cholesterol, and atherosclerosis; psychological risk factors of type A personality and/or an inability to handle stressful events; and social risk factors of smoking, diet, and activity level.
Biologically, depression is associated with changes in various neurotransmitter levels and activity, commonly referred to as a chemical imbalance in the brain. Additionally, depression frequently runs in families, suggesting a genetic, or heritable, aspect to the illness. Medical conditions and sometimes the medications used to treat those conditions can also cause depressive symptoms. Psychologically, certain personality types are more prone to developing depression. People who have low self-esteem and a pessimistic outlook are at higher risk for depression. Other psychological disorders, such as anxiety, psychotic, or substance abuse disorders, increase the odds of developing depression. Socially, depression is linked to stressful life events, usually entailing loss, such as of a spouse, child, job, or financial security. Depression, however, can also be linked to events generally considered to be uplifting rather than stressful, although from the body’s reaction, they are stressful. These events can include marriage, the birth of a child, a job change or promotion, or a move to a new neighborhood or home.