Julie A. Phillips, Ashley Robin, Colleen Nugent, and Ellen Idler report (partially gated):
Our analysis of suicide rates among the middle-aged for the period 1979–2005 showed a substantial increase in suicides by men aged 50–59 years and women aged 40–59 years between 1999 and 2005, following a period of stability or decline in rates for these groups. Suicide rates also increased for younger middle-aged men between 1999 and 2005, but we found that this increase was better characterized as a continuation of previous, ongoing trends for this group. The post-1999 increase for all cohorts was found among both married and unmarried members, although the risks were higher for unmarried people. The rise was particularly dramatic for those without a college degree, while those with a college degree appeared largely protected from the trend. The timing of the increase coincided with the complete replacement of the U.S. population’s middle-age strata by the postwar baby boom cohorts, whose youngest members turned 40 years of age in 2004.
Here is a related press release and it mentions substance abuse and chronic disease (more of a rude awakening for them?). Here are some speculations about the rising rate; one possibility is that regulatory warnings have to some extent discouraged anti-depressant drugs. Here is a related paper, on measurement and considering a few possible explanations. It seems there is no comparable rise for African-Americans.