im certain that he didnt die from diabetes but from the skin dyes, tablets and injections that allowed his skin to go black. He died alittle later when he finished writing the book and wasn't alive to see the influence it had on American society.
He died in 1980, 19 years after 'Black Like Me' was published you tool. He died of diabetes just accept it.
I had always heard he passed away from what the skin dyes did to him as well.