Obese young men between 14 and 20 years of age have only half the testosterone levels of their leaner counterparts, and a high likelihood of infertility as adults, found a team of US researchers led by Indian-origin professor Paresh Dandona.

Researchers from University at Buffalo, New York, reported as early as 2004 that low testosterone levels, or hypogonadism, was found in obese, type-2 diabetic adult males. The finding from the university's School of Medicine and Biomedical Sciences was confirmed in 2010 in more than 2,000 obese men, both diabetic and non-diabetic.

"We were surprised to observe a 50 percent reduction in testosterone in this (latest) paediatric study because these obese males were young and were not diabetic," Dandona, professor of medicine at Buffalo and head, Division of Endocrinology, Diabetes and Metabolism, who led the study, was quoted as saying by the journal Clinical Endocrinology.

"The implications of our findings are, frankly, horrendous because these boys are potentially impotent and infertile. The message is a grim one with massive epidemiological implications," Dandona said, according to a Buffalo statement.

The small study included 25 obese and 25 lean males. Concentrations of total and free testosterone and estradiol, an estrogen hormone, were measured in morning fasting blood samples. The results need to be confirmed with a larger number of subjects, Dandona says.

"These findings demonstrate that the effect of obesity is powerful, even in the young, and that lifestyle and nutritional intake starting in childhood have major repercussions throughout all stages of life," he said.

In addition to the reproductive consequences, the absence or low levels of testosterone that were found also will increase the tendency toward abdominal fat and reduced muscle, leading to insulin resistance, which contributes to diabetes.

"The good news is that we know that testosterone levels do return to normal in obese adult males who undergo gastric bypass surgery," Dandona said.

"It's possible that levels also will return to normal through weight loss as a result of lifestyle change, although this needs to be confirmed by larger studies," he said.

The researchers now intend to study whether or not weight loss accomplished either through lifestyle changes or through pharmacological intervention will restore testosterone levels in obese teen males.