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What Causes PCOS?


Updated June 18, 2014

What causes PCOS?

While researchers are not certain of the exact cause of PCOS, it is known that an imbalance of the endocrine system is responsible for many of the changes associated with PCOS. However, it is still not known exactly what causes those changes.

The Hypothalamic-Pituitary-Ovarian Axis

Hormones are proteins produced by a structure within the body that causes a change within a cell or organ. The Hypothalamic-Pituitary-Ovarian (HPO) axis is a system of hormonal control within the body. The hypothalamus is a gland within the brain that, when stimulated, produces a hormone, known as Gonadotropin-Releasing Hormone or GnRH. GnRH travels to the pituitary gland, another small structure in the brain. The pituitary gland produces a variety of other hormones which regulate and maintain many body functions.

Of significance to PCOS, the pituitary produces FSH, or Follicle Stimulating Hormone, and LH, or Lutenizing Hormone. LH travels to the ovary where it stimulates the production of androgens. It has been hypothesized that persistently high levels of LH and androgens, namely testosterone, causes PCOS. However, this does not explain why many women with PCOS do not have high levels of LH.

The Insulin-Androgen Connection

Insulin has been thought to have a role in the development of PCOS. In addition to regulating glucose levels, insulin causes the liver to decrease production of a key molecule known as sex-hormone binding globulin, or SHBG. Testosterone is carried in the blood by SHBG when the molecule is present. If a reduced amount of SHBG is available, more free testosterone (testosterone that isn't carried by SHBG) is in the blood. It is also believed that high levels of insulin can increase the amount of androgens that the ovary produces. This also does not fully explain PCOS, as many women with PCOS do not have insulin resistance, a change in how body cells react to insulin, and a common issue seen in PCOS.


Researchers are currently trying to identify if genetic abnormalities may be at fault. This is made difficult due to the lack of a single diagnostic test as well as the role that external factors (such as obesity, diet and exercise habits) may play in the development of the disease. Most physicians do believe there is a genetic link, although at this time it's not known exactly what that link may be.


Harris, Colette and Carey, Adam. PCOS: A Woman's Guide to Dealing with Polycystic Ovary Syndrome.Thorson; London. 2000.

Thatcher, Samuel. PCOS: The Hidden Epidemic. Perspectives Press; Indianopolis. 2000.

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