The 650 muscles in the human body control movement and help to maintain posture, circulate blood and move substances throughout the body.

Testosterone therapy, in which testosterone is administered to men with low levels of the hormone, has been a controversial topic, with some advocating for the therapy as a way to restore vitality in older men, but others are concerned about the health conditions, such as heart problems and cancer, it may bring along.

Now, a new study shows that men taking testosterone therapy for just over half a year could gain a few pounds of muscle mass and lose a corresponding amount of body fat.

But while the authors find the study encouraging, it may not do much to change the minds of those skeptical of the risks and benefits.

While other research has also established that testosterone can help build muscle mass, there are concerns that it may raise the risks for prostate cancer. And some studies, such as a Boston University study published in the New England Journal of Medicine last year – a study that was ended early because of these very concerns — have shown an increased risk for heart problems on men taking the therapy.

"By and large, the medical community is not certain [about the] benefit from testosterone," said Dr. John Amory, an internist who researches the effects of testosterone at the University of Washington.

The study was published online Dec. 6 in the Journal of Sexual Medicine.

Testosterone and muscles

Researchers from Beth Israel Deaconess Medical Center in Boston measured the testosterone levels in the blood of 58 men, and started them on testosterone therapy. At the outset, 20 of the men had low testosterone levels, and 38 had normal levels but had other symptoms associated with low testosterone, such as erectile dysfunction, a reduced sex drive and fatigue. They were followed for roughly six months, and given testosterone as a topical gel or as injections.

The study was retrospective, Amory noted, meaning that patients were not randomized to receive or not receive testosterone. Instead, the researchers grouped them by their testosterone levels – but all were being treated anyhow.

While muscle mass increased in those treated, Amory said, it was only about 2.5 pounds. "The effect is not that marked," he said.

But the study's senior author said the muscle gain and fat loss were more than they might seem.

"That may or may not sound impressive, but for most of us, if we were to gain a pound of muscle, it would actually feel quite significant," said Dr. Abraham Morgentaler, urologist and founder of Men's Health Boston, the hospital clinic where the study was run.

Morgentaler is an advocate for testosterone therapy and an author of "Testosterone for Life: Recharge Your Vitality, Sex Drive, Muscle Mass, and Overall Health" (McGraw-Hill, 2009). He said concerns about the therapy are excessive.

The risk of developing prostate cancer, or of an existing cancer growing, may be mitigated by testosterone, Morgentaler said, citing to a recent small study he led where 13 men with prostate cancer did not see their cancer worsen while on testosterone therapy.

While that study was too small to say if testosterone was harmless, Morgentaler said that "it certainly shows that the old fear that higher testosterone necessarily causes rapid prostate cancer growth cannot be true."

About the Boston University study that was stopped early, Morgentaler said that while the number of heart events was high, they were not as severe as one might expect, and may not be because of the testosterone.

That study "came as a surprise, and created quite a stir because we live in a society that is very focused on medical risk," he said. "It's important to realize what that study showed, and what it did not show."

First, he said, the patients in the study were older men and relatively frail. As to the heart risks, he said. "When we hear about cardiovascular risks, normally what we think of is heart attacks and strokes.” In that study, there were only two heart attacks and…one stroke.” (Other heart events included trouble breathing and irregular heartbeat.)

That study included 209 men, whose average age was 74.

"In my opinion, these results were simply an aberration, which is something that happens in medical science all the time," Morgentaler said.

For now, the debate goes on.

"It's a risk-benefit [analysis]. It's very similar to the situation with estrogen for women," Amory said. "Doctors of good faith can disagree about things when there's an absence of data."

An answer?

Amory said that some of that disagreement should be cleared up by an ongoing randomized clinical trial, which is expected to be completed in 2015.

That study, known as The Testosterone Trial, is expected to enroll 800 men, and is being led by Dr. Peter Snyder at the University of Pennsylvania and sponsored by the National Institutes of Health.

Each participant will apply a topical testosterone gel, or a placebo, to his chest or arms daily, and the researchers will monitor factors such as walking speed, memory and sexual activity, to see if the treatment is having its intended effect.

Morgentaler is less optimistic the trial will provide an answer. He said that while it may help with acceptance of the therapy, the timeline is not long enough for a thorough investigation of risk associated with prostate cancer.

"I think it's an important study, but it's not going to be able to address everything," he said.

For now, Amory likens the debate to the one surrounding hormone replacement therapy. Older women were routinely given estrogen, until a large study found that this raised the risk of breast cancer. So now, fewer women are given the treatment, and it is restricted to those with strong indications they will benefit.

While there are some cases, Amory said, where testosterone appears to have clear benefits, such as young men who for medical reasons have their testicles removed and need testosterone, it's less clear how widely the treatment should be used in older men seeking added vitality

"What we don't know — in the 65-year-old man who is having sexual problems, obesity, maybe some other problems… does the testosterone do more good than harm?"

This story was provided by MyHealthNewsDaily, a sister site to LiveScience. Follow MyHealthNewsDaily on Twitter @MyHealth_MHND. Find us on Facebook.