There are of course some comprehensive sites on the web that will give very much more detailed information than can be briefly outlined here. The cautionary note is however to go to reliable sites, like mayo clinic's as an example for unfortunately there is a lot of very unreliable and misleading information as well. It is probably best to try to answer as you asked:
1. More women than men present for treatment with depression
. This is partly a societal problem of men having greater difficulty, in general, expressing their feelings and being able to allow themselves the expression of emotions, such as crying
. We have certainly seen a dramatic change in the society's acceptance. If you look up when sen. Edmund muskie became tearful because his wife was being attacked in the newspapers during the 1968 presidential campaign and he was viewed as "weak." contrast that with the matter of fact way that mr. Speaker john boehner's tearfulness is accepted. It took some 50 years, but we are getting there.
2. Good nutrition
, sufficient sleep
, regular exercise
, and an attitude that avoids the "rut of helplessness" are good steps to avoid or dampen the biology of a depressed state or disposition. Omega 3 fatty acids (found especially in oily fish like salmon) has been shown to be useful. There is a nature and nurture element that acts in developing depression. The things mentioned speak to the nuture aspect.
3. The symptoms of depression are not difficult to identify when there is a full blown manifestation with sleep and appetite
disturbances, doom and gloom attitude, suicidal ideations, and absence of any sense of pleasure now, remembered from the past, or seem possible in the future. The disease of depression is a diagnosable condition and not just a "normal" reaction to the "slings and arrows" of life.
4. Re-read the first answer and i think you will find the correlation of difficulty feeling allowed to express emotion
and being suicidal. Keep in mind that no one who suicides really wants to die, they just hope to get rid of the pain. Unfortunately, there is no encore when lethal means are used, which is the mode most men use (guns) vs. Women (pills).
5. We are as a species social animals and so human connectedness is vital. There are many patients who might consider it a blessing not to have "downer" families! there are social groups of all sorts to which one can reach out, but first things first. That is, getting the person relieved from the depression through every reasonable means available with medication and the things mentioned before.
Do go into deeper depth with your interest through reliable web sites and the many good books available.