The new study was carried out by scientists at the University of Oxford in the United Kingdom, and the findings were presented at the National Cancer Research Institute (NCRI) Cancer Conference, held in Liverpool, U.K.

To the authors' knowledge, this is the first time that scientists have examined how low levels of testosterone affect the risk of prostate cancer. Their research is also the largest study of the link between hormones and prostate cancer to have ever been conducted.

Prostate cancer affects more than 170,000 men each year in the United States, of whom almost 30,000 die from the disease.

While it is not yet known what causes the condition, researchers have identified a number of risk factors, such as age, ethnicity, and genetic mutations.

Male hormones, or androgens, such as testosterone are known to promote tumor cell growth in men with prostate cancer. Lowering or blocking testosterone levels in the body is the standard treatment for prostate cancer because androgens help the prostate cancer cells to grow.

The so-called androgen saturation model proposes that in order to grow, prostate tissue — whether malignant or benign — needs just enough testosterone for the androgen receptors to be saturated.

However, after the saturation point has been reached, any further increase in testosterone does not lead to an additional increase in prostate tissue or cancer tumor growth.

As the authors of the new study explain, "[B]ecause the saturation point is thought to be low, until now there have been insufficient prospective data available to test this theory."

So, the team set out to fill this research gap by testing the theory in more than 19,000 men.