Feature: What really causes depression?

             Depression is likely one of the most affecting mood disorders in today’s world. But what is depression? What causes it? Depression is a mood disorder characterized by a persistent low or sad mood, absent or lessened interaction in most activities, loss of self-confidence, and a feeling of worthlessness. The causes of depression remain fairly enigmatic. Countless theories attempt to explain what causes depression, whether they be grounded on unconscious memories or learned behaviors. However, in our opinion, there is overwhelming evidence that suggests depression is caused by various biological factors, and can therefore be treated through a biological approach.

            The development of depression has been linked to imbalances in three of the brain’s important neurotransmitters: serotonin, norepinephrine, and dopamine. Neurotransmitters are chemical messengers that pass messages between neurons by crossing the synaptic gaps between neurons in the brain. Lower than normal levels of these specific types of neurotransmitters can cause depression. These low amounts of serotonin, norepinephrine, and/or dopamine are unable to stimulate the receiving neuron, causing neurons not to fire signals as often as they should or as is normal. Therefore, a lower amount of action potentials takes place. The chemical imbalances and lower amount of action potentials caused by the lack of dopamine, serotonin, and norepinephrine neurotransmitters lessen activity in the areas of the brain that control mood, which ultimately results in depression.

            Aside from imbalances in the brain’s neurotransmitters, imbalances in brain structures may also cause depression. Chemical imbalances affecting the limbic system may be another biological cause of depression. The limbic system is a ring of structures in the brain and includes the amygdala, hypothalamus, and hippocampus. This brain system is associated with many emotions, such as fear, aggression, and depression. Since the limbic system is associated with emotions, chemical imbalances that affect it may lead to a change in emotions or depression.  Furthermore, the hippocampus, which plays a role in memory, is smaller in some depressed people, and research suggests that ongoing exposure to stress hormones impairs the growth of nerve cells in this part of the brain. The amygdala is a part of the brain that deals with emotions like sorrow, fear, anger, and pleasure. The brains of depressed people have higher activity in their amygdala, suggesting this part of the brain is associated with the mood disorder.

            Depression has also been linked to genes. For example, if one identical twin has a mood disorder such as depression, there is close to a 46% chance that the other twin will also suffer from depression, while this is only true for about 20% of fraternal twins. Identical twins share more genes than fraternal twins do, so this higher occurrence of depression among identical twins suggests depression may be linked to genes. This idea is supported by the fact that adopted children whose biological parents were depressed are more likely to develop depression than their non-biological siblings raised in the same home.

            Medical conditions or disorders can also lead to depression. Dementia that causes brain disorders like Alzheimer’s disease can make people more susceptible to depression. Hypothyroidism, a condition in which your body produces too little thyroid hormone, often leads to exhaustion and depression. Vitamin deficiencies have also been linked to depression.

            There are many different manners of combating depression. Antidepressants are drugs that are commonly described to depressed people. These drugs, such as selective serotonin reuptake inhibitors (SSRIs) block the reabsorption of neurotransmitters by the sending neuron and leaves them in the synapse, where they can be better available to stimulate the receiving neurons.

            In retrospect, biological factors can describe the causes of depression. Although it is not completely known, we are aware that biology plays a big part in depression, as evidenced through the differences or imbalances in neurotransmitters or parts of the brain and genes.