Is it not due to the increase in stress d/t racial discrimination and violence (especially against young African-American males)? We have known for years that the onset of any illness is more likely following stressful events, and the more stress, the more likely. A simple way to measure the stress might be keeping count of the murders of African-Americans, which is surely accessible in newspaper archives, and might be something that someone at NAACP or law-enforcement agencies are tracking. Good luck with this--it is an important question.
Actually, I am mistaken about the homicide rate. According to the Bureau of Justice Statistics, black males are the demographic most likely to be victims of homicide, but the rate of homicides actually peaked during the 1990's, and has fallen. It is still higher than it was in the '70's and '80's. It seems like we are hearing more about the murders now. Is it just being reported more, or perhaps are we talking about it more?