Depression is a potentially life-threatening mood disorder that affects 1 in 6 persons in the United States, or approximately 17.6 million Americans each year. Depressed patients are more likely to develop type 2 diabetes and cardiovascular disease. Not counting the effect of secondary disease states, over the next 20 years, unipolar depression is projected to be the second leading cause of disability worldwide and the leading cause of disability in high-income nations, including the United States.
As many as two-thirds of people with depression do not realize that they have a treatable illness and do not seek treatment. Only 50% of persons diagnosed with major depression receive any kind of treatment, and only 20% of those individuals receive treatment consistent with current practice guidelines of the American Psychiatric Association (APA). [2, 4] More alarming, in a large Canadian study, 48% of patients who had suicidal ideation and 24% of those who had made a suicide attempt reported not receiving care or even perceiving the need for care.
The cause of depression is multifactorial. A family history of depression is common among persons with the disorder, as is a family history of suicides.
In addition to depression, other factors such as alcohol/substance abuse (especially of opiates and cocaine), impulsiveness, and certain familial factors may greatly increase the risk for suicide. These include a past history of mental problems or substance abuse, suicide in the immediate family, a family violence of any type, and separation or divorce.
Other risk factors include prior suicide attempt(s), presence of a firearm in the home, incarceration, and exposure to the suicidal behavior of family members, peers, celebrities, or even highly publicized fictional characters. It is also established that the initiation of treatment for depression with psychotherapeutic agents can temporarily increase the incidence of suicidal ideation as well as energize motivation, and therefore, unfortunately, can increase the likelihood of successful suicide attempts. The incidence of depression in healthcare workers is comparable to that in the general population, though the rate of completion of suicide is higher. Therefore, healthcare workers diagnosed with depression, especially when coupled with burnout or substance use disorder, should be considered to be an in a higher risk category for attempted or completed suicide.
This statistics below are from Medscape
African Americans and Mexican Americans are least likely to receive any care, let alone adequate care, for depression. 
The BRFSS study by the CDC noted that non-Hispanic blacks (4%), Hispanics (4%), and non-Hispanic persons of other races (4.3%) were significantly more likely to report major depression than non-Hispanic whites (3.1%). 
Suicide rates among American Indian and Alaskan natives aged 15-34 years are almost twice the national average for this age range. Hispanic females make significantly more suicide attempts than their male or non-Hispanic counterparts.
The risk of suicide is increased by concurrent illness, alcohol and drug abuse, access to lethal means, hopelessness, pessimism, isolation, and impulsivity, and the risk are reduced by help-seeking behavior, access to psychiatric treatment, and availability of family and other social supports.
More women than men seek treatment for depression, but this is not necessarily reflective of the true incidence of the disease. The BRFSS study by the CDC determined that women were significantly more likely than men to report major depression (4% vs 2.7%, respectively). 
Although depression is more often diagnosed in women, more men than women die as a result of suicide by a factor of 4.5:1. White men complete more than 78% of all suicides, with 56% of suicide deaths in males involving firearms. Poisoning is the predominant method among females.
An estimated 8-25 attempted suicides occur for every completion. Many of these are never discovered or never reported. It is critically important to recognize that the majority of suicide attempts are expressions of extreme distress in a very ill individual, and are categorically not, as has often been assumed historically, merely bids for attention.
According to the BRFSS study by the CDC, the prevalence of major depression increased with age, from 2.8% among individuals aged 18-24 years to 4.6% among individuals aged 45-64 years; however, incidence declined to 1.6% among those 65 years or older.  The study also found that “other depression” was highest (8.1%) among individuals aged 18-24 years.
Suicide is estimated to be the eighth leading cause of death in all age ranges in the United States. The highest suicide rates are found in men older than 75 years. However, suicide is also a selective killer of youth. It is the third leading cause of death among people aged 15-24 years, after unintentional injuries and homicide, and the second leading cause of death in college students. The mean age for successfully completed suicides is 40 years.
Here a Story from Buzzfeed.com about a Guy battling with his depression.
For a few years in my early twenties, it was my job to drink. Every day, every night, as much as possible. I had other jobs, ones that paid, but those came and went and were just ways of making money, money that I would spend on a sea of bottles. I was alone and confused, carrying barbed memories from my childhood that squirmed in a thorny tangle inside my chest, but would stretch out through my mouth or up into my mind if I didn’t battle them back down with alcohol. I didn’t have any ambition, or any interest in finding my way. Being drunk and sad and alone was my job — and you know what? I didn’t hate it. Being lost at sea was a comfort.
Luckily for me, even though I felt alone, I wasn’t. Slowly strangers became acquaintances, and acquaintances became friends. Some were a lot like me, and others weren’t. But all of them became shipmates, I a part of their crew and they a part of mine. Even just talking to them loosened the tangled monster that gripped me, enough for me to find another star — that of forgiveness — to light my way. I forgave, not because the things that I remembered were resolved or any sort of justice was served, but because I was willing to let go. There is still a tangle inside of me, but I’m not as frightened of it. Once in a while, the memories do send their despairing tendrils up into my mind and flow out of my mouth as speech, but even when things seem darkest, I have the first two stars that helped me navigate into safer waters: friendship and forgiveness.
Suicide Hotline & Helpline Information
National Suicide Prevention Lifeline
Crisis Text Line
Text START to 741-741