Etiology of Depression

1. Excessive Drug Use

1.1. There is a bi-directional relationship between drug use and depression. Drug and alcohol use in excess may lead to feelings of excess fatigue and loneliness and over extended periods of time, depression. People with depression are also more likely to resort to substance abuse.

2. Chronic Illness & Pain

3. Structural factors

3.1. Neurogenesis

3.1.1. This process is most active during prenatal development but acts even through adult years.

3.1.1.1. People who don’t endure depression naturally maintain a balance of the degradation and regeneration processes of neurons in the brain.

3.1.1.2. However, it seems those struggling with depression show greater activity in the degradation system and vice versa.

3.2. Researchers have found that there is a significant difference between the size of the hippocampus in people who have had a history of depression than those who haven't. The hippocampus is responsible for storing memories.

4. Genetics

4.1. Caspi et al suggested that people who inherit two short versions (alleles) of the 5-HTT genes (5-hydroxy-tryptamine gene), one from each parent are more likely to develop major depression after a stressful event (refer to my genetics and inheritance cards if you wanna enhance your knowledge). 5-HTT gene makes the serotonin transporter protein which affects levels of the brain's chemical serotonin. Low-levels of serotonin may be linked to depression. The risk of depression due to this greatly increases if a person is subjected to lots of stressful events.

4.2. Researchers found a recently isolated gene that connects family members to the possibility of experiencing depression. This is associated with the 3p25-26 chromosome.

5. Hormonal factors

5.1. Cortisol

5.1.1. The stress hormone cortisol is produced in excess in a depressed person.

5.2. Serotonin

5.2.1. Serotonin is a feel good chemical. An imbalance of serotonin has lead to several disorders with respect to mood.