Can insulin cause the prostate to grow?

Insulin can prompt prostate cells to divide and enlarge by switching on growth signals. Studies in people and experiments with cells describe insulin and a closely related growth hormone as molecular drivers of prostate cell growth. Insulin resistance, a condition in which the body needs ever-increasing amounts of insulin to keep blood sugar in check, plays a central role in this connection.

Men with higher insulin resistance at the start of a large study involving nearly 5,000 men had a measurably larger prostate volume. This association was statistically clear, both in men without and in men with urinary complaints. It does not, however, say anything about cause and effect: it is a correlation, not proof that insulin resistance enlarges the prostate.

Insulin resistance is part of the metabolic syndrome, a combination of excess weight, high blood sugar, high blood pressure and an unhealthy distribution of body fat. Many studies combined show that men with metabolic syndrome have a larger prostate than men without it: the difference ranges from around 2 ml in mixed Western populations to as much as 10 ml in Asian studies. The prostate also grows more quickly each year. A large British study of nearly 164,000 men, followed for more than 13 years, showed that metabolic syndrome raises the risk of an enlarged prostate by about 7%. Within metabolic syndrome, excess weight and low HDL cholesterol are the strongest predictors of prostate enlargement.

Notably, a larger prostate does not automatically mean more complaints. In several combined analyses, men with metabolic syndrome did not have notably more or worse urinary symptoms than men without it. Insulin resistance also turned out not to be an independent predictor of urinary complaints developing or worsening. The link between insulin and the prostate therefore runs primarily through volume, not through the symptoms you actually experience.