A high lean body mass - calculated using an equation to determine body mass minus the fat - may lower the risk of prostate cancer, a new study indicates.

Prostate cancer is a hormone-related disease affected by a variety of other factors including genetics, age, ethnicity and family history. In the last few years, researchers started to suspect that body size might also affect the risk of prostate cancer, but research has provided conflicting results.

Most studies investigated body mass index, but this index includes lean and fat tissue, which may have different influences on the risk of cancer.

In an attempt to settle things, Dr. John S. Witte from the University of California, San Francisco, and his colleagues conducted a study of 439 men with prostate cancer and 479 of their siblings without prostate cancer.

They examined the effects of weight, height, body mass index, and lean body mass, which they thought might be more relevant than body mass index to the risk of prostate cancer and aggressiveness of the disease.

The researchers found that the higher the lean body mass, the lower the risk of prostate cancer, especially in men with more aggressive disease or who were older when their cancer was diagnosed. They also observed a similar, though weaker, inverse pattern for weight, but found no associations between risk of prostate cancer and body mass index or height.

The investigators suspect that the inverse associations between higher lean body mass and prostate cancer risk may reflect the potentially protective effect of high levels of the male hormone androgen in patients with high lean body mass on the development and progression of prostate cancer.

SOURCE: Journal of Urology, December 2005.