| This sounds like the supervisor in question lacks knowledge...at least in this area. I would report this to not only the next superior in line, but to a total of 3 levels minimum. I've found that many levels protect each other...or try to brush what they fear is a lawsuit between the cracks.
By reporting to several levels of management, you are "educating" more people. Explain that you are not asking for any special treatment that is not beyond that of any other diabetic who is working hard and doing a good job.
I'd also probably try to find a new job with a more "progressive" company. But, that's my own opinion of working for boobs. | 
