The fact that conditions such as sleep apnea (insufficient nocturnal brain oxygenation) lead to depression and anxiety in a significant number of cases illustrates that depression isn't always an indicative of a social problem. It can also be a strictly biochemical issue (there are a lot of things that affect neurotransmitter efficiency for instance).
My point was, depression can come from a variety of sources; not just environmental or biochemical. Saying it's generally those two sources glazes over all the others - and is not representative.
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