For many years, physicians have regarded insulin-managed diabetes to be a contraindication to diving. Both Carl Edmonds, renowned expert in dive medicine, and Peter Bennett, executive director of the Divers Alert Network, note in their respective dive medicine books that the risks involved make a diabetic who requires insulin an unfit candidate for diving. They both qualify that statement by saying that under some circumstances, people who control their diabetes through diet and exercise could be allowed to dive. The greatest potential risk to diabetic divers is having a hypoglycemic episode while under water. This can be precipitated by too much insulin, too little food, or a variety of stresses, including exercise.
Severe hypoglycemia can result in weakness, seizures and unconsciousness.
These episodes are extremely unpredictable, even in well-controlled diabetics, and the early warning signs, such as sweating, nervousness and hunger could be difficult to detect or interpret correctly while under water. The dangers of a hypoglycemic episode while diving are obvious. The other risks diabetic divers face stem from the secondary complications of diabetes, most notably the effects on the blood vessels. Diabetics, for reasons that are not completely clear, develop atherosclerosis much earlier than comparable nondiabetics. This can affect not only the heart, leading to an increased risk of heart attack, but also the legs, resulting in early cramping and limited exercise tolerance.