What are the causes of depression?The most commonly known symptom of depression is sadness. Having said that, we should be aware that depression is a much more complex disease, characterised (besides low mood and feeling of helplessness on daily basis) by losing interest in previously enjoyed activities, tiredness, loss of energy, sleeping problems, suicidal thoughts, feelings of guilt, reduced concentration and attention.
What are the factors which cause depression?There is no conclusive answer to that question. In the face of current knowledge, depression factors are genetic predisposition, physical condition and situational factors like traumatic or stressful events. What is worth knowing is that we can divide depression into two kinds: endogenous and reactive depression.
GeneticsGenetical factors are substantial for disease onset. The percentage of co-occurrence of depression in identical twins ranges between 40-50 %, whereas in fraternal twins stands at 25%. The risk of developing the disease for relatives ranges between 10-25%. There is no “depression gen” found thou. The predisposition to fall into the depressive episode is probably conditioned to a couple of different genes which interacts with triggers in the person’s environment.
NeurotransmittersThe most popular hypothesis explaining the causes of depression was created in the second half of the 20th century. The catecholamines hypothesis of affective disorders and the serotonin hypothesis of depression. Both of them suggest the deficiency in neurotransmitters called catecholamine. Noradrenaline(NA), dopamine(DA) and serotonin(5HT) shortage in the neurological system result in disease onset. The serotonin hypothesis was made when there was observed the influence on the depressive effect on individuals taking medicine like reserpine which decrease catecholamine and serotonin concentration. Another revelation was made when it was found out that the antidepressive effect might be caused by monoamine oxidase inhibitors (MAO) and tricyclic antidepressants – what was proved on animals models. Mentioned hypothesises comes from research in which the tryptophan restrictions in diet, decreased the serotonin amount. In the group of participants with no depression risk, there was noo differences after applied manipulation, whereas with participants in disease remission there were depression symptoms observed. Neurotransmitters disturbance in brain tissue was researched using neurochemical and molecular-genetic as well as neuro-imaging. What is also worth mentioning, is the influence of stressful factors on genes expression.
NeurohormonesNeurobiologists highlight the impact of so-called “stress axis”, limbic-hypothalamic-pituitary-adrenal axis (HPA) on our wellbeing. Since the ‘80s there have been accumulated evidence proving that overactivity of HPA is related to depression occurrence by raising the level of cortisol, changing it’s day-and-night rhythm and increasing secretion of corticoliberin and activity disturbance of intrinsic glucocorticoid receptors. It is worth mentioning that there are other neurohormonal axes like hypothalamic–pituitary–thyroid axis (HPT) responsible for thyroid hormones secretion, depressive mood and procreation. There is the visible tendency for affective disorders raised appearance in premenstrual, postnatal and early menopause period which can shed some light on the influence of sex hormones on female depression.
Stressful eventsEarly years exposure as well as experiencing stressful events when being an adult strengthen the risk of depression. Experiencing stress when being a child might be the cause of “central stress response system” dysregulation and lower the resilience for stressful events in adulthood. The risk factors for children are losing a parent/parents, long term separation from parents, sexual or physical abuse. The adults are more prone to the disease when experience death of a family member or a friend, problems at work or losing a job, a rapid decrease of interpersonal relation. Those events appear mostly about a few days, weeks or even months before the episode of depression. Having said that, there is no scientific evidence for any specific life events history as a predictor of depression. It happens that people who experienced traumatic events don`t suffer from depression. Conversely, sometimes depression appears even though there are no changes in the person`s environment.
“To understand the molecular mechanisms of depression, collect genetic data from more than 100000 people.”, says Steven Hyman Director of the Stanley Center for Psychiatric Research
There is no known specific factor which causes depression. Depression is probably an effect of multiple endogenous factors – genetics, physiology and situational. There are also protective characteristics within the person. The situational factors realise depression only when there is a biological vulnerability present. For the last 60 years, treating depression is based on pharmacology which was discovered by coincidence. For the reason of less coincidence and more knowledgeable solutions we need to examine and understand depression causes.
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- Depression needs large human-genetics studies, Hyman, Steven.Nature; London (Nov 13, 2014): 189-91.