PCOS is an endocrine-metabolic disorder in which insulin resistance (IR) plays an important role in 50-70% of women with PCOS, regardless of their weight. Insulin resistance reduces the ability of cells to process glucose normally, resulting in an accumulation of glucose in the blood (hyperglycaemia). The body compensates by secreting more insulin, resulting in elevated levels of insulin (hyperinsulinaemia).
Insulin has several different functions, particularly on the metabolism of carbohydrates, fats and proteins. Understanding these may help you understand your symptoms and treatment.
Insulin is a hormone produced by the pancreas. Production is mainly regulated by the levels of glucose in the blood. When the concentration of glucose is high, insulin secretion increases and when the level of glucose in the blood decreases, insulin production decreases as well.
Insulin exerts its function by binding to a specific receptor (a protein located in the cell membrane). In this way insulin indirectly governs the intracellular metabolic machinery to produce the desired effects without the need to enter the cell. The binding triggers many biological processes in which myo-inositol is a key component.
Insulin resistance is characterised by reduced metabolic efficiency of insulin in, for example, muscle and fat tissue; they have decreased sensitivity to insulin. Although IR is not one of the 3 diagnostic criteria, testing of blood glucose levels, fasting insulin and a protein, SHGB, may help identify alterations in insulin sensitivity. Recently it was suggested that the levels of SHBG can be used as a biomarker of IR as it has been shown that insulin reduces the synthesis of SHBG by the liver. The main role of SHBG is to mop excess sex hormones, including testosterone, so a lack can lead to elevated levels of circulating testosterone.
Although the cause of PCOS is not known exactly, it is clear that hyperinsulinemia usually plays a key role in the development of the syndrome.