As men get older, the levels of testosterone in their blood often drop. This drop in testosterone has been hypothesized to lead to various things, such as decreased sexual function, anemia, and bone breaks.

Testosterone supplementation is used by some physicians to help with such bodily issues. In recent years, there has been increased interest in the clinical utility of testosterone supplementation in older men.

However, large, long-term studies have not been performed to figure out whether testosterone treatment actually helps with such conditions. In 2003, an Institute of Medicine panel concluded there was insufficient evidence supporting the benefits of testosterone in older men and recommended further research.

Consequently, in 2010, the National Institute of Aging, which is part of the National Institutes of Health, launched the Testosterone Trials (T Trials) to see whether testosterone can help with symptoms associated with low levels of testosterone secondary to older age (i.e., symptomatic hypogonadism).

The T Trials will serve as a prelude to lengthier and more robust trials in the future. Results from the T Trials are coming in and overall results are mixed, with testosterone replacement associated with some benefits and some risks.

More research needs to be done to figure out the balance of these potential benefits and risks as well as the precise clinical utility of testosterone treatment.

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T Trials Overview

The T Trials are a set of seven clinical trials hosted at 12 sites around the country. In the aggregate, 790 men aged 65 or older with low levels of testosterone and associated symptoms participated.

First, participants had to qualify for one of the main three trials, the:

Sexual Function Trial

Physical Function Trial

Vitality Trial

Then, participants could participate in any of the other trials for which they qualified. People were excluded who had certain conditions, such as prostate cancer, heart problems, kidney problems.

In all the trials, participants were randomly assigned to either an experimental or placebo group.

Men in the experimental group applied a testosterone gel daily (AndroGel) for 12 months; the placebo group received a placebo gel (without testosterone). Participants were regularly assessed.

Importantly, the trials were double-blinded, meaning that the researchers and the participants didn't know which gel was administered.

Sexual Function, Physical Function, Vitality

Results from the first three trials were reported in February 2016 in the New England Journal of Medicine.

Inclusion in the Sexual Function Trial required participants to have a decrease in libido along with a sexual partner willing to have intercourse two times a month.

Inclusion in the Physical Function Trial required participants to have slow gait speed, difficulty walking, and difficulty climbing stairs. Men who couldn’t walk, had severe arthritis, or had severe neuromuscular disease were excluded.

Inclusion in the Vitality Trial required participants to have fatigue and low vitality.

Raising testosterone levels from low to a normal range improved sexual function modestly (i.e., sexual activity, sexual desire, and erectile function) as well as mood and depressive symptoms. However, testosterone supplementation didn’t improve walking ability or vitality.

Overall, the researchers suggest that there weren’t enough participants to draw definitive conclusions in these three trials.

Anemia Trial

In February 2017, results from the Anemia Trial were published.

Anemia is a condition in which there’s a deficiency of red blood cells or hemoglobin in the blood. In one-third of elderly men with anemia, clinicians can’t establish a cause.

With anemia, the body doesn’t receive enough oxygen-rich blood, which is carried by hemoglobin located in red blood cells. Anemia can be mild or severe. People with anemia can feel weak or tired. Other symptoms include dizziness, shortness of breath, or headaches.

Long-lasting anemia can damage the heart, brain, and other organs. Occasionally, very severe anemia can result in death.

The Anemia Trial was performed to figure out whether older men with unexplained anemia and low testosterone levels could experience improvement in their hemoglobin levels.

Results from the clinical trial demonstrated that there were significant increases in hemoglobin in both men with unexplained anemia as well as men with anemia from known causes who used the testosterone gel.

These results may be of clinical value, and testosterone treatment could be used to boost hemoglobin levels in men more than 65 who have unexplained anemia and low testosterone. However, more research needs to be done.

Bone Trial

In February 2017, results from the Bone Trial were published.

As men age, they not only experience decreases in testosterone levels but also decreases in bone mineral density, bone volume, and bone strength as well as an increase in bone fractures.

Prior research concerning the effects of testosterone on bone has been inconclusive. With the Bone Trial, researchers tried to figure out whether bone density increased after testosterone treatment in older men with low testosterone levels.

Bone density was evaluated using dual energy x-ray absorptiometry (DEXA), and bone strength was evaluated using computed tomography (CT) scans.

CT is an imaging method that uses X-rays to take cross-sectional pictures of the body. DEXA scans use low-dose X-rays to assess bone mineral density and compute scores. In other words, DEXA scans measure how much calcium and other minerals are in the bone.

Except for over-the-counter vitamin D and calcium supplements, men taking medications affecting bone were excluded from the study. Additionally, men with low DEXA scores were excluded from the study.

The researchers found that men who received hormone treatment experienced an increase in bone strength and density. Strength increases were greater in the spine than they were in the hip.

However, as with other T Trials, more research needs to be done. A larger study over many years would need to be performed to determine whether testosterone could decrease the risk of bone fracture.

Cognitive Function Trial

In February 2017, results from the Cognitive Function Trial were published.

According to Resnick and other authors of the study:

"Aging is associated with declines in some cognitive functions, including verbal and visual memory, executive function, and spatial ability. Aging in men is also associated with a reduction in serum testosterone, raising the possibility that reduced circulating testosterone concentration may contribute to age-related cognitive decline."

In this study, older men with low testosterone and age-associated memory impairment were given testosterone. Age-associated memory impairment was defined by memory complaints and impaired performance on tests of verbal and visual memory.

This study didn’t show that testosterone treatment helped with age-associated memory impairment.

Cardiovascular Trial

Studies concerning the effects of testosterone on cardiovascular outcomes are conflicting.

The Cardiovascular Trial was designed to determine whether testosterone supplementation in older men with low testosterone levels could slow the development of noncalcified coronary artery plaque volume.

Noncalcified coronary artery plaque volume has been linked to heart attack and ensuing heart problems. It’s tested using coronary computed tomographic angiography, a special diagnostic test.

The researchers found that in men taking testosterone gel, there was a significant increase in noncalcified coronary artery plaque volume. This finding is concerning because an increase in plaque volume decreases coronary artery blood flow, which could be damaging. Coronary arteries supply the heart with blood.

Again, as with other T Trials, more research needs to be done to figure out the true implications of this study.

Bottom Line

The results of these studies indicate that testosterone treatment in older men with low testosterone may proffer some benefits.

However, testosterone treatments may also entail risks. The exact trade-off is unknown. Larger and longer studies need to be performed to clarify the effects of testosterone on heart health, bone health, disability, and more.

An important thought to keep in mind when it comes to low testosterone is that measurement of this hormone is a bit tricky—one single result should not be taken at face value. This is for the following reasons:

Testosterone levels—even in healthy people—fluctuate through the day. So a completely healthy person can have normal T levels in the morning and low levels in the afternoon. For this reason, testosterone is always measured at 8 to 9 a.m. and usually repeated if low.

Borderline low-level results usually don't signify much, and the number has to be clinically low (below ~230 ng/dL) to justify an evaluation for T therapy.

A Word From Verywell

If you’re an older man with low testosterone and interested in taking testosterone, this decision should be carefully considered with your physician.

Your doctor will be able to better assess the balance of your conditions and whether hormone replacement could put you at potential risk.

It's a bad idea for anybody to engage in hormone supplementation without a doctor's supervision. Just because hormones occur naturally in the body does not mean that they can be taken without negative effects.

Finally and for good measure, consider this parting guidance regarding the T Trials from the NIH:

"Because the T Trials were conducted in older men with no apparent cause for low testosterone other than aging, these results don’t apply to men with low hormone levels for reasons other than aging. Any man considering hormone treatment should discuss the possible harms and benefits with a health care provider."