Here's an article published today which also states my points in this thread, which are that social isolation - not having friendships or relations with family - is the cause of depression. The article refers specifically to teenagers, who have the highest rates of suicide next to the elderly, though the research can be applied to any age group. Note that the elderly also have high rates of suicide, due to the lack of social connection because their companions die off.
Researchers Outline Effective Strategies to Prevent Teen Depression and Suicidehttps://www.sciencedaily.com/releases/2012/11/121115162132.htmEDIT:
I have never seen any research suggesting that it's common to get severely bipolar simply because of life conditions without predisposing inborn (or very early developed) changes in brain chemistry. I'll be happy to read some if you know of any studies. Usually people have been bipolar a long time before they were diagnosed. Depression in some form I agree can hit almost anyone, but it is clear that some people are far more likely than others. There's already gene research suggesting that there are genes that predispose to depression.
I'm not aware of any research into bipolar manic depression as a social symptom. As far as I've read, it is considered a medical issue and as a result, it is not investigated as a social one.
I guess I can speak about bipolar manic depression from my personal experience with it. I'm not diagnosed with it (as I've never seen a psychiatrist) but my symptoms are textbook descriptions. My closest friend has a son who is diagnosed with it, and she thinks that I have it too, though not severely. I will also attempt to explain why the manic episodes occur.
The depressive stage is the most frequent and stable of the two. The severity can range from lethargy to thoughts of suicide. However, actually feeling bad to the point where I can say it is depression is not often, even though I know I am in a state of depression. No one knows that I am depressed, not even friends or family. They think I'm joking when I tell them I will buy a gun and shoot myself in the head, after laying a tarp to keep my brains from making a mess too difficult to clean without professional help. Falling on my head and splitting my skull open isn't dramatic enough.
The manic phase is short and infrequent with bursts of optimism and the belief that I can do anything within reason based on my assessments of my abilities. Incredible bursts of creativity can occur but that depends on what resources I have at hand to express it. If the resources are available, I will engage in it. If not, then I just go off in my imagination.
This manic phase is a period where I don't feel any self-doubt. I think this occurs when the parts of my brain that are responsible for the cause of my depression simply go to sleep.* When it goes to sleep, I am released and the manic phase, which has been very well rested, comes out. The brain functions as either excitatory or inhibitory and the depression functions as inhibitory.
* Research shows that the brain does not necessarily go to sleep altogether and that different parts can sleep at different times, even when fully awake. Also, parts of the brain will sleep after significant neural load, such as after a hard practice session at the piano.