insulin sensitivity

Insulin is a hormone made by the pancreas, and its job after a meal is to move glucose out of the blood and into the cells that will use or store it. The National Institute of Diabetes and Digestive and Kidney Diseases describes insulin resistance as the state in which the body does not respond to insulin the way it should, with cells in muscle, fat and liver answering the signal poorly. Insulin sensitivity is the same axis read from the other end: the more sensitive a tissue is, the less insulin it takes to get the same work done.

The organs do not have to move together, which is why a careful study reports muscle and liver separately. In skeletal muscle, sensitivity is a question of how much glucose is pulled out of the blood for a given amount of insulin. In the liver the signal runs the other way, because insulin tells the liver to stop making and releasing glucose of its own, so sensitivity there is a question of how readily that release shuts off. A person can be sensitive in one tissue and resistant in another, and a treatment can move one without moving the other.

The institute sets out what follows when cells respond poorly: the pancreas may not manage to make enough insulin to keep pushing the extra glucose into them, and glucose then builds up in the blood. That is the road to prediabetes, which it defines as blood glucose higher than normal but not high enough to be diagnosed as type 2 diabetes, marked by an A1C of 5.7 to 6.4 percent, a fasting plasma glucose of 100 to 125 mg/dL, or a two-hour oral glucose tolerance test result of 140 to 199 mg/dL. What causes insulin resistance in the first place is not fully understood. The institute notes that in the Diabetes Prevention Program, participants who lost 5 to 7 percent of their starting weight reduced their chance of developing type 2 diabetes.