Dehydration. When there’s extra sugar in your blood, you pee more. That’s your body’s way of getting rid of it. A large amount of water goes out with that urine, causing your body to dry out.
Weight loss. The glucose that goes out when you pee takes calories with it. That’s why many people with high blood sugar lose weight. Dehydration also plays a part.
Diabetic ketoacidosis (DKA). If your body can't get enough glucose for fuel, it breaks down fat cells instead. This creates chemicals called ketones. Your liver releases the sugar it stores to help out. But your body can’t use it without insulin, so it builds up in your blood, along with the acidic ketones. This combination of extra glucose, dehydration, and acid buildup is known as "ketoacidosis" and can be life-threatening if not treated right away.
Damage to your body. Over time, high glucose levels in your blood can harm the nerves and small blood vessels in your eyes, kidneys, and heart. They can also make you more likely to get hardening of the arteries, or atherosclerosis, which can lead to heart attacks and strokes.