It’s normal to experience feelings of sadness and grief from time to time. But when these feelings are prolonged or interfere with daily life, they may be symptomatic of depression. 
Depression can affect anyone regardless of age, gender or economic status. The National Institute of Mental Health says around 350 million people worldwide suffer from depression. Understanding depression can help those dealing with the disorder.

What is depression?
Depression is a mood disorder that causes persistent feelings of sadness and loss of interest. The Mayo Clinic says depression can produce a variety of symptoms and affect the way a person thinks, acts and feels. Symptoms may include changes in sleeping patterns, anxiety, fatigue, weight gain or weight loss, unexplained aches and pains, and difficulty concentrating.

What causes depression?
Although the cause of depression remains a mystery, certain distinguishing factors are common among those who have the condition. People with clinical depression appear to have physical changes in their brains. In addition,  naturally occurring brain chemicals known as neurotransmitters likely play a role in depression. The Mayo Clinic states changes in the function and effect of these neurotransmitters and how they interact with neurocircuits involved in maintaining mood stability may play a significant role in depression and its treatment. 
In addition to biological factors in the brain, hormones can impact rates of depression or even trigger it. These hormone shifts may be a leading reason why women have higher incidence rates of depression than men. Depression is more common in people whose blood relatives also have the condition. Therefore, those with a family history of depression may be more likely to get it than those without such a connection.

Different types of depression
There are different types of depression. A person may have a single bout of major depression or  recurring episodes. Depression that lasts two or more years is called persistent depressive disorder. A less common type of depression is called manic-depressive illness. This involves cycles of depression that alternate with extreme highs, or manias.

Treating depression
Depression is a very treatable condition. Psychotherapy (talk therapy), medications or a combination thereof can be very effective in managing symptoms. Mental health professionals can work with individuals to find the right therapy based on symptoms and severity of the depression. Also, it may take some time to find the right medication or treatment; therefore, people are urged to remain patient and hopeful.
The National Institute of Mental Health says people who suspect they may be suffering from depression should make an appointment to see a doctor or health care provider. The sooner action is taken, the more quickly the condition can be addressed.