Diabetes was medical condition in humans. According to Oliver Morgenstern, dizziness could be a sign of early on-set diabetes. (TV: Smith and Jones) Obesity was a known cause of diabetes. (PROSE: Slow Decay)
People with diabetes had to take shots; Danny was diabetic, and offered his syringe to inject Jack Harkness with EDTA and cure his cyanide poisoning, saying that his diabetes "finally comes in handy". (TV: Rendition)
Mike told Gwen Cooper and Ianto Jones that Barry had been cured of his diabetes thanks to The Pharm. (TV: Reset)
The Eleventh Doctor swapped places with a diabetic stripper called Lucy who was to burst out of a cake for Rory Williams' stag night. After bursting out of the cake, he said that she was outside in a bikini and asked if someone could let her in and give her a jumper as she was a lovely girl and diabetic. (TV: The Vampires of Venice)