With testosterone treatment, fat turned to muscle in men with diabetes.
Senior author Dr. Paresh Dandona, of the Department of Medicine in the Jacobs School of Medicine and Biomedical Sciences at the University of Buffalo (UB), NY, and his coauthors already knew that low testosterone levels coincide with significantly decreased insulin sensitivity.
In 2004, they demonstrated a link between low testosterone levels and type 2 diabetes.
Six years later, they extended this to obesity. In a study of more than 2,000 men, they observed that 33% of participants with type 2 diabetes, whether obese or not, had low testosterone levels, as did 25% of non-diabetic, obese males.
In 2012, the team found that teenage boys with obesity have 50% less testosterone than their lean peers.
The researchers had also associated obesity with oxidative stress and inflammation. Inflammatory mediators are known to interfere with insulin signaling.
Testosterone: anti-inflammatory and insulin-sensitizing?
In the present study, the team hypothesized that testosterone may be an anti-inflammatory and insulin-sensitizing agent, since it has been known for some time that testosterone reduces adiposity and increases skeletal muscle.
The participants were 94 men with type 2 diabetes, of whom 44 had low testosterone levels.
Before treatment, those with low testosterone levels expressed significantly lower levels of insulin-signaling genes and diminished insulin sensitivity.
The men with low testosterone were randomized to receive a testosterone injection or a placebo every week for 24 weeks.
Testosterone did not change the men's body weight, but there was a reduction in total body fat of 3 kilograms (more than 6 pounds), while muscle mass increased by the same amount.
There was also a dramatic increase in insulin sensitivity, demonstrated by a 32% increase in the uptake of glucose by tissues in response to insulin, and a similar increase in the expression of the major genes that mediate insulin signaling. Fasting glucose levels also diminished significantly, by 12 milligrams per deciliter.
Patients' hemoglobin A1C (HbA1c) levels did not go down - a necessary indicator that testosterone can help control diabetes. However, Dr. Dandona believes that a significant improvement in HbA1c might be seen in longer-term studies.
Could testosterone be a metabolic hormone?
Dr. Dandona says this is the first definitive evidence that testosterone is an insulin sensitizer and hence a metabolic hormone.
"Testosterone treatment for men, where indicated, will improve sexual function and increase skeletal muscle strength and bone density."
For future studies, the UB researchers are interested in how testosterone treatment may impact insulin resistance and inflammation in specific patient populations, such as those with chronic renal failure and hypogonadism.
Dr. Dandona and his colleagues have previously reported that 2 in 3 men with type 2 diabetes, men who have chronic kidney disease also have low testosterone levels. Among patients on dialysis, a remarkable 90% have low testosterone.
Medical News Today recently reported that eating more homemade food may reduce the risk of type 2 diabetes.