And over the last two decades, it's men without college degrees who have ended up most disconnected from the core institutions of work, marriage, and civil society. Guess who is most likely to kill themselves? Men without college degrees. In fact, according to recent research by sociologist Julie Phillips and her colleagues, suicide has surged in recent years (this research covers the period up to 2005) among precisely this group of less-educated middle-aged men, even as suicide remained essentially stable among middle-aged men with college degrees over this period.

Source: Current Population Survey, 1990-2010

Take work. The chart above indicates that middle-aged men without college degrees are about twice as likely to have recently experienced spells of unemployment. Given that one study found that unemployed men were 126 percent more likely to kill themselves, the deteriorating economic fortunes of poor and working-class men have likely played a key role in the recent spike in suicide among middle-aged men without college degrees.

Or take marriage. The chart below indicates that middle-aged men without college degrees are much less likely to be married than their college-educated peers, either because they got divorced or never married in the first place. This matters because Phillips' work indicates that unmarried men are about 240 percent more likely to kill themselves, compared to their married peers. Thus, in all likelihood, the nation's dramatic retreat from marriage among less-educated men in recent years has also had a hand in rising rates of suicide among this group of men.

Source: Current Population Survey, 1990-2010

So, as experts trot out their pet theories to explain the recent rise in suicide among middle-aged American men, it's worth keeping in mind that suicide is highest, and climbing fastest, among precisely those men whose ties to the larger social fabric—and to work and women, in particular—have become the most attenuated.