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SAN FRANCISCO–Testosterone replacement therapy increases insulin sensitivity among men with type 2 diabetes, an ongoing clinical trial shows. Preliminary results were presented Tuesday at The Endocrine Society’s 95th Annual Meeting in San Francisco.

“Our studies have shown that having low testosterone also impacts insulin action, and that can be corrected by testosterone replacement,” said study lead author Paresh Dandona, DPhil, distinguished professor and chief of endocrinology at the State University of New York at Buffalo.Testosterone replacement increases efficiency of insulin action in men with type 2 diabetes.

Since testosterone is the main male sex hormone, insufficient production affects many aspects of men’s health, including sexual functioning, bone and muscle health, and energy level. One of the many causes of low testosterone production is obesity, and approximately 25 percent of obese men produce insufficient amounts of the hormone.

Insulin is a hormone secreted by the pancreas that acts to reduce the level of sugar, or glucose, in the blood. In the most common form of diabetes, type 2, the pancreas does not produce enough insulin. The disease is also characterized by insulin resistance, which means that the cells that normally convert glucose into energy ignore the insulin that is produced. One-third of men with type 2 diabetes have low testosterone levels. One of the main indications for testosterone replacement therapy is the treatment of sexual dysfunction.

Previous research by the current study’s investigators showed that low levels of testosterone are associated with greater insulin resistance, and that hormonal replacement can increase the body’s sensitivity to insulin. The precise relationship between low testosterone and insulin sensitivity, however, is unclear.

Preliminary results from this study show that men with type 2 diabetes who also have low testosterone levels were more resistant to insulin than men with normal testosterone concentrations. Furthermore, hormone replacement therapy decreased their insulin resistance.

Other findings show that testosterone replacement therapy is associated with an increase in muscle mass and a corresponding decrease in fat tissue. Specifically muscle mass increased by 2 kilograms, or 4.4 pounds, among men who received testosterone therapy, while fat-tissue mass decreased by the same amount. In addition, testosterone replacement therapy was associated with less tissue inflammation, which indicates a decrease in insulin resistance.

After enrolling, participants are assigned to one of four groups: type 2 diabetes + low testosterone; type 2 diabetes + normal testosterone; obesity + low testosterone; or obesity + normal testosterone. Each group receives testosterone replacement therapy for six months. Investigators then measure participants’ insulin sensitivity, and their percentage of muscle- and fat-tissue mass. They are assessing inflammation in blood, muscle and fat samples. Their work also shows that testosterone replacement in patients with low levels of this hormone suppresses inflammatory factors which are responsible for interfering with the action of insulin and thus explains the mechanisms responsible for resistance to the action of insulin in such patients.

So far, 50 men are participating in the study. Their average age is 53, and they are either diabetic, obese or both. Investigators plan to enroll another 150 participants for the study, which will conclude a year from now.

The National Institutes of Health is funding the study.

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Founded in 1916, The Endocrine Society is the world’s oldest, largest and most active organization devoted to research on hormones and the clinical practice of endocrinology.  Today, The Endocrine Society’s membership consists of over 16,000 scientists, physicians, educators, nurses and students in more than 100 countries. Society members represent all basic, applied and clinical interests in endocrinology. The Endocrine Society is based in Chevy Chase, Maryland. To learn more about the Society and the field of endocrinology, visit our site at Follow us on Twitter at!/EndoMedia.