Insulin is a hormone that is produced by the beta cells, which are cells that are scattered throughout the pancreas. The insulin produced is released into the blood stream and travels throughout the body. Insulin is an important hormone that has many actions within the body. Most of the actions of insulin are directed at metabolism (control) of carbohydrates (sugars and starches), lipids (fats), and proteins. Insulin also is important in regulating the cells of the body, including their growth.
Insulin Resistance (IR) is a condition in which the cells of the body become resistant to the effects of insulin; that is, the normal response to a given amount of insulin is reduced. As a result, higher levels of insulin are needed in order for insulin to have its effects. The resistance is seen with both the body’s own insulin (endogenous), and if insulin is given through injection (exogenous).
Insulin Resistance-related PCOS (Polycystic Ovarian Syndrome), also known as polycystic ovaries, leads to the release of excess insulin, a condition known as hyperinsulinemia. Ovaries seem to be particularly sensitive to high blood levels of insulin, and respond by overproducing male hormones (androgens) like testosterone, which cause PCOS symptoms such as infertility, excessive hair growth, male pattern baldness and acne. Hyperinsulinemia can also lead to dyslipidemia of insulin resistance; high TGL, low HDL, and small dense LDL, which increases the risks of a heart attack.
The link between insulin resistance and cancer may be related to the compensatory high levels of insulin. Insulin is an important growth factor for body tissues. That insulin is an important growth factor is not surprising, because typically insulin increases when nutrients are plentiful, and drops dramatically during a fasting state. Insulin may signal cells to proliferate through a variety of mechanisms. Insulin could directly signal growth, or it could do this by increasing the levels of other more potent growth factors (insulin-like growth factors [IGF]); or it can make cells more sensitive to other growth factors.
Although cancer is a complex, multifactorial disease, one of the consistent characteristics of cancer cells is their ability to grow uncontrollably and to be less resistant to die. Thus, growth factors are critical to the initial development of cancers and to their progression. A number of studies now show that individuals with higher levels of circulating IGFs are at increased risk for developing colon, premenopausal breast, and aggressive prostate cancers than are individuals with lower levels.
Although insulin resistance is characterized by cells becoming less sensitive to the effects of insulin to transport glucose into cells, insulin insensitivity does not seem to lower the growth-promoting properties of insulin. Only the glucose transporting properties are affected in insulin resistance. Thus, in an insulin resistant state such as induced by obesity, the higher circulating levels of insulin may have a cancer-promoting influence for at least some tissues. As long as the pancreas can continue to produce large amounts of insulin in the face of insulin resistance, some individuals may avoid diabetes; however, these individuals may be the ones most susceptible to cancer because they have the highest circulating insulin concentrations.