A new medical study, which is well summarized here at PsychCentral finds a strong correlation between depression in men and lower testosterone levels.
This link has definitely been talked about for a long time, and is one of many biological issues that might cause depression.
When I am working with men who are depressed or have depressive symptoms, I always suggest having a checkup with a medical professional, hopefully with some blood tests.
Some of the other things a blood test can turn up which can cause depressive symptoms are thyroid conditions and vitamin D deficiency.
Part of the reason I suggest the checkup is that trying to find psychological, emotional or situational reasons for depression when it actually has a stronger physical cause can be a wild goose-chase.
And while I have your attention, let’s not forget some of the things you can try yourself to ease depressive symptoms: cardio exercise, good sleep, less alcohol, and a better diet.