Long-standing Diabetes, especially if poorly-controlled (blood sugar often too high) can damage nerves. This is most famous for affecting sensation in the feet (leading to amputations). But it can also affect the Autonomic Nervous System, which controls involuntary function of body organs.
If nerves in the gastrointestinal tract don’t work well, a variety of manifestations are possible. These include diarrhea, constipation, stool incontinence, swallowing problems, and stomach bloating. In the cardiovascular system, it can cause heartbeats which are too fast or too slow, and dizziness upon standing (due to loss of blood pressure control in the arteries), among others. It’s notorious for causing impotence and loss of vaginal lubrication, and it can result in various types of abnormal sweating.
Unfortunately, once the damage has been done, we can’t help very much. Prevention always works better, like keeping good control of blood sugar.