Insulin is a naturally occurring hormone that uses sugars found in foods as fuel. People with type 1 diabetes don't make enough insulin to survive and must inject insulin to stay alive. If you have more sugar in your body than it needs, insulin helps store the sugar in your liver and releases it when your blood sugar level is low or if you need more sugar, such as in between meals or during physical activity. As blood sugar levels rise, the pancreas secretes more insulin. If your body does not produce enough insulin or your cells are resistant to the effects of insulin, you may develop hyperglycemia (high blood sugar), which can cause long-term complications if the blood sugar levels stay elevated for long periods of time.
