Depression–it’s an increasingly common disease that doesn’t seem willing to offer any respite. The World Health Organization (WHO) estimates that at least 322 million people worldwide suffer from depression, 18% more than a decade ago. Also known as major depressive disorder, clinical depression is characterized by a persistent feeling of sadness, loss of interest, cognitive impairment, and sleep and appetite problems. It is a recurring and costly disease that often becomes chronic, causing suffering and disability.
What causes depression? Unfortunately, we don’t know. However, there are numerous studies on its risk factors–the characteristics and circumstances that increase the probability of depression.
Some are common sense risk factors such as dramatic life events–the death of a loved one or the diagnosis of a serious illness. However, there are many other lesser-known but important risk factors. These include sociodemographic factors, genetic and neurological factors, personal factors, adverse experiences, and comorbidity.
Sociodemographic factors: twice as many women are depressed
Perhaps the most consistent and well-known sociodemographic risk factor for depression is gender. Regardless of country or culture, post-pubescent women are twice as likely to experience depression as men.
However, researchers have identified other sociodemographic risk factors for depression such as age, marital status, educational level, and race. Depression occurs more frequently among whites, young adults, single adults, separated or divorced couples, and individuals with lower educational levels. Depression is also found to be more common among low-income populations, the unemployed, and urban residents.
Genetic factors: depression can be inherited
Immediate family members of patients with depression are three times as likely to develop the disorder. Studies indicate that 26-42% of variations in depression are due to genetic influences. There is also some evidence that early-onset and recurring depression is more likely to be inherited. However, no specific gene or set of genes has been reliably associated with depression or in parental transmission–the disease is too heterogeneous.
Neurological factors: the amygdala becomes overactive
Neural abnormalities have been documented in certain brain regions of adults with depression. Specifically, these are structural abnormalities in the gray matter volumes of the hippocampus, amygdala, anterior cingulate cortex, and dorsolateral prefrontal cortex.
When we become depressed, neural function also changes. There is increased brain activation in the subcortical regions of emotion processing, such as the amygdala and limbic circuits, combined with attenuated activation in the cognitive control regions.
This doesn’t only happen in adults. The same abnormalities in neural function and structure have been identified in children of parents with depression, even before the onset of a depressive episode. This is why experts believe these children are more vulnerable to this disorder.
Personal factors: introversion and excessive self-criticism
A proclivity for negative emotions (fear, anger, sadness, and anxiety), as well as mood swings and negative thoughts–known as neuroticism–are personal factors that lead to a higher risk of experiencing a depressive episode.
Introverts are also more likely to experience depression. These are individuals who prefer solitary activities, and are more focused on their own thoughts, feelings, and moods than on seeking external stimuli.
Research also indicates that a relationship exists between depression and low levels of conscientiousness. This is characteristic of individuals who are aimless, casual, lazy, careless, undisciplined, and weak-willed.
Excessive self-criticism (feelings of guilt and failure from unrealistically high self-expectations) and dependence/sociotropy (feelings of helplessness and fear of abandonment due to a high emotional dependence on others) are also predictors of depression.
Another attitude that fosters depression is what is known as negative attributional style. This is the tendency to attribute negative experiences to internal, stable, and global causes. For example, “I didn’t get the job because I’m useless and always have been.”
Something similar occurs with mental rumination, which is continuously thinking about the same sad or dark thoughts, which focuses attention on depressive symptoms and their implications, causes, and meanings for oneself.
Finally, deficits in personal resources (social skills, appropriate problem-solving strategies, and coping skills in stressful circumstances) are also related to an increased risk of depression.
More than 40 years of research has documented the role of traumatic life events in the onset of depression. Depending on the type of sample studied, approximately 50-80% of people with depression reported a traumatic or severe life event prior to the onset of the disorder.
We could conservatively say that people with depression are 2.5 times more likely to have experienced a severe life event prior to onset than those with no depression. Typical traumatic life events include life-threatening health problems, separation and bereavement, exposure to violence, job loss, and financial insecurity.
Equally important are cataclysmic events or phenomena in which a single, sudden, and powerful event affects large numbers of people. These events are often beyond the control of any individual or group, and are regarded as being universally stressful–like the Covid pandemic.
Negative childhood events also put us at risk for depression as we grow up. These include physical and sexual abuse, psychological neglect (or abandonment), exposure to domestic violence, parental mental illness, and criminality. People with a history of childhood trauma (especially bullying and emotional abuse or neglect during childhood) are more than twice as likely to develop depression.
One of the most striking aspects of depression is that it is often accompanied by other mental disorders, specifically anxiety disorders, substance abuse disorders, eating disorders, and sleep problems.
Furthermore, any chronic or severe medical condition can be a risk factor for depression. Depression has been found to be associated with a wide range of physical illnesses: acute myocardial infarction, asthma, cancers, cardiac arrhythmia, chronic coronary syndrome, chronic obstructive pulmonary disease, congestive heart failure, some neurological diseases such as Alzheimer’s or epilepsy, thyroid problems, diabetes, obesity, some pathologies of the digestive system, hypertension, osteoarthritis, osteoporosis, renal failure, rheumatoid arthritis, stroke, fibromyalgia, chronic fatigue, and more.
Recognizing all these risk factors can help us understand depression better, prevent the onset of the disease, and perhaps slow its seemingly inexorable advance.