Insulin

What it is

Insulin is a hormone produced by the pancreas (beta cells of the islets of Langerhans). Its main role is to allow cells to absorb blood glucose and use it as energy or store it. After a meal, blood glucose rises, the pancreas secretes insulin, cells take up glucose, and blood glucose falls again.

Insulin also acts on other tissues: the liver, muscles, adipose tissue, and the ovaries. It is this action on the ovaries that makes it particularly important in PCOS.

Insulin resistance in PCOS

Insulin resistance is a state in which cells respond less effectively to the insulin signal. To compensate, the pancreas produces more — this is called compensatory hyperinsulinaemia. Blood glucose can remain normal for years, masking the underlying problem.

It is present in 30–80% of people with PCOS according to studies, and independently of body weight — it can affect lean people as well as those who are overweight.

In PCOS, hyperinsulinaemia creates a particular problem: the ovaries retain normal sensitivity to insulin even when the muscles and liver are resistant. Excess insulin directly stimulates ovarian theca cells to produce more androgens, which can amplify hyperandrogenism and disrupt ovulation.

How it is assessed

Measuring fasting insulin alongside fasting blood glucose allows calculation of the HOMA-IR (Homeostasis Model Assessment of Insulin Resistance), an index that estimates insulin resistance. It is not an absolute diagnostic test, and thresholds vary by population and laboratory.

An oral glucose tolerance test (OGTT) with insulin measurements at multiple time points may be offered in some cases for a more complete assessment.

Key takeaways

• Pancreatic hormone that regulates blood glucose and acts on the ovaries
• Insulin resistance present in 30–80% of people with PCOS
• Independent of weight: can affect lean people too
• Hyperinsulinaemia → ovarian stimulation → more androgens
• Assessed via HOMA-IR or OGTT, always interpreted by a doctor