What is insulin resistance?
Insulin is a hormone produced by the beta cells in the pancreas. Small amounts of it are normally released after each meal to help transport glucose into the body's cells, where it is needed for energy production. Insulin resistance is a decreased ability to respond to the effects of insulin, especially by muscle and fat (adipose) tissues. Since cells must have glucose to survive, the body compensates for insulin resistance by producing additional amounts of the hormone. This results in a state of hyperinsulinemia in the blood and over-stimulation of some tissues that have remained insulin sensitive. Over time, this process causes an imbalance in the relationship between glucose and insulin and can cause an unhealthy ripple effect in the body.
Hyperinsulinemia and insulin resistance can affect the proportion of the body's lipids, significantly increasing the amount of triglycerides and sdLDLs (small dense lipoproteins) in the blood and decreasing the amount of HDL (high density lipoprotein, the "good cholesterol"). It may also increase a person's risk of developing a blood clot, cause inflammatory changes, and increase a person's sodium retention, which can lead to increased blood pressure.
Insulin resistance is not a disease or specific diagnosis, but it has been associated with conditions such as cardiovascular disease (CVD), hypertension, polycystic ovarian syndrome (PCOS), type 2 diabetes, obesity, and nonalcoholic fatty liver disease. Some researchers also believe that there may be a link between insulin resistance and some forms of cancer. The mechanisms of these associations, however, are not well understood. It is important to remember that many of the people who have these conditions do not have insulin resistance and, likewise, many of the people who have insulin resistance will never develop these conditions. These are just patterns of association that have emerged. They are frequently seen together and it is thought that insulin resistance may contribute to their development and exacerbate them when it is present.
Metabolic syndrome and insulin resistance are two terms that have often been used interchangeably to characterize some of the abnormalities associated with increased resistance to insulin and increased production of insulin, and to recognize these changes as risk factors for future disease. Metabolic syndrome is essentially a subset of insulin resistance, with a focus on identifying obese, sedentary people who are beginning to experience alterations in their lipid levels and impaired glucose processing. The goal of this identification is to work with these people to decrease their health risks through lifestyle changes.
The cause of insulin resistance is not fully understood. It is thought to be due partly to genetic factors, including ethnicity, and due partly to lifestyle. Most patients with insulin resistance do not have any symptoms – they do not realize that this process is taking place in their bodies. In most cases, the body is able to keep pace with the need for extra insulin production for many years. If or when the body's insulin production fails to keep up with demand, then hyperglycemia will occur. Once glucose levels reach a high enough level, diabetes is present; the high glucose levels can damage blood vessels in many organs, including the kidneys. Insulin resistance that is associated with these high glucose levels is a risk factor for developing type II diabetes. Changes in lipids can cause fatty plaque deposits in the arteries and lead to cardiovascular disease and strokes.