Testosterone Has Benefits for Metabolism, Weight Loss

Louise Gagnon

July 18, 2012

July 18, 2012 (Quebec City, Canada) — More than 4 years of testosterone therapy resulted in significant weight loss and a reduction in waist circumference in hypogonadal men, according to data presented here at the 3rd International Congress on Abdominal Obesity (ICAO).

"All these patients presented [to a urologist] because of erectile dysfunction," said Farid Saad, PhD, DVM, director, Global Medical Affairs Andrology, Bayer HealthCare Pharmaceuticals, Bayer Pharma AG, Berlin, Germany. "They received 4 years of testosterone therapy without interruption. To our surprise, we saw that they lost weight, and this was neither intended nor expected."

The investigators prospectively followed up 130 men with an average age of 58 years who had late-onset hypogonadism. Patients were diagnosed with a total serum testosterone level of 3.5 ng/dL or less and erectile dysfunction, defined by a score of 21 or less on the Sexual Health Inventory for Men. They were administered 1000 mg long-acting testosterone undecanoate (TU) by intramuscular injection and followed up for a median of 4.7 years.

Treatment was initiated on day 1, with a second dose administered 6 weeks later. Injections of TU were then given at 3-month intervals. Investigators measured weight and waist circumference at baseline and at every subsequent TU treatment.

Dr. Saad's team observed significant changes in numerous parameters including measured weight, waist circumference, percentage weight loss, and body mass index.

Specifically, they found that the mean weight decrease from baseline to the last patient visit was 14.3 kg, with 2 patients losing 40 kg or more. The mean percentage weight loss was 13.0%, body mass index (BMI) decreased by a mean of 4.5 points, and the mean decline in waist circumference was 11 cm.

Low testosterone is associated with low energy and low motivation to be active, so the administration of testosterone might have led to increased physical activity, which the study did not control for, said Dr. Saad.

"We hypothesized that these men become more active as their testosterone levels are restored. They have an increase in vitality and energy," Dr. Saad told Medscape Medical News.

In most weight loss studies, patients display a U-shaped curve in their weight loss, where they regain weight at 6 to 12 months follow-up, he noted, but patients in this study experienced ongoing weight loss and did not regain their weight.

An increased level of activity would potentially increase muscle mass and decrease fat mass, contributing to a faster metabolic rate in patients, which would contribute to weight loss, said Dr. Saad. The effect of testosterone supplementation on physical activity has not been well-studied, he added.

Another phenomenon that may be occurring is that the reduction in adipose tissue is sparking production of testosterone, he suggested.

"We know that obesity and adipose tissue suppress testosterone production," said Dr. Saad. "If the adipose tissue goes away, the suppression of the body's own testosterone production no longer happens."

Ultimately, patients who present with low testosterone may not require indefinite testosterone supplementation if they experience weight loss and suppression of testosterone production ceases, said Dr. Saad.

"If men are losing weight and leading more active lifestyles, they may be able to go without supplementation," he said.

Michael Jensen, MD, endocrinologist and professor of medicine, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota, and member of the international advisory board for the International Chair on Cardiometabolic Risk, said the resulting weight loss, decreased waist circumference, and decreased BMI may be attributable in part to lifestyle changes.

This study population is also quite heterogeneous in terms of their baseline testosterone levels, so it is hard to determine the metabolic effects of the testosterone supplementation, he pointed out.

"As an endocrinologist, I would want to know how many had a pituitary disorder, how many had a gonadal disorder, and how many were just fat," said Dr. Jensen.

Dr. Saad is an employee of Bayer Pharmaceuticals AG, and the company is performing further statistical analysis of the study, which it did not fund. Dr. Jensen receives grant funding from Abbott Pharmaceuticals Inc.

3rd International Congress on Abdominal Obesity (ICAO): Poster 179. Presented July 11, 2012.

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