Beta cells in the pancreas produce a hormone to control the amount of sugar (glucose) in the blood. This hormone, insulin, serves as a gatekeeper, allowing glucose to enter the body's cells and be used as energy. All humans—and animals—need insulin to survive.
Insulin was discovered in 1921 and quickly became indispensable in treating people with type 1 diabetes, who have lost the ability to make their own insulin. People with type 2 diabetes may also require insulin therapy when their own beta cells don't produce enough of the hormone. Insulin must be administered by injection or through an insulin pump because, if taken orally, it would be destroyed by the digestive system.
Even though insulin is a naturally occurring protein, researchers have tweaked it in the laboratory to produce insulin "analogs" that act more like the body's own insulin. For example, some insulin analogs are meant to provide a slow release of insulin over 24 hours. Others are designed to be used at meal times, providing a quick burst of insulin to help the body metabolize the glucose in a meal.