Here's what the current research says.
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Earlier this year, scientists at the National Institutes of Health announced the latest results of the "T Trials." A $50 million project initiated in 2009, the T Trials are the largest-ever study of the effects of testosterone treatments on men—in this case almost 800 men aged 65 and over who started out with confirmed low testosterone levels.
This may sound like niche research. Yet testosterone treatments are a $2 billion market (and growing at a fair clip), consumed not just by those with clinically low "T" but also by average men sold on controversial advertising narratives that a boost of the hormone can improve their mood, sex drive, energy, and generally claw back against the effects of aging—perhaps even improving their longevity. Rather than settling debates over T treatments' effects and the claims of some of their promoters, though, these latest results just added ambiguity, showing that some patients' bone strength and anemia improved, while some suffered increased risks of cardiovascular events.
"We have no consensus and a lot of conflicting evidence that needs to be sorted out," says Sherman Harman, an endocrinologist working in the Phoenix Veterans Affairs Health Care System who's studied the effects of T treatments. Some of this confusion stems from a lack of study rigorous enough to make grand claims, especially for average men looking for a health boost. Testosterone may also just have contradictory effects. Either way, it's okay to speculate and push for research on the possible health merits and demerits of T, but this ambiguity means that the general public shouldn't be taking it as a miracle cure—and the T treatment market probably shouldn't be this massive.
The raging debates over testosterone's general health properties may be confusing to those who know it just as a sex hormone, controlling male characteristics like musculature, body hair, and vocal timbre, as well as sex drive. However testosterone affects the wider body as well in diverse and profound ways—as becomes clear in men with abnormally low testosterone (a rare condition with various causes), who have their testosterone lowered to fight prostate cancer, or as their T levels naturally start to lower by about one percent a year after age 30 or 40. Beyond causing the loss of sex drive and musculature, men with very low testosterone tend to gain weight and can sufferer from a range of mood, cognitive, and potentially other physical issues as well.
Proponents of T treatments say they can reverse such negative symptoms and likely generally benefit health, especially for aging men. "We have a wealth of data from a variety of sources that are highly suggestive that a higher level of testosterone occurring naturally or testosterone treatment in men who are deficient in [it] may actually help with cardiovascular risk" among other issues, says Abraham Morgentaler, a doctor at Boston's Men's Health clinic and author of Testosterone for Life: Recharge Your Vitality, Sex Drive, Muscle Mass, And Overall Vitality. Morgentaler admits it's hard to tell if low T levels are the primary cause of negative symptoms, and that low T can itself be a symptom of something else. But if taking T treatments helps with health issues, he adds, then that's a sign of its potential. And testosterone's ability to potentially combat the ravages of aging, he says, "suggests that testosterone is pretty good for longevity."
Opponents, meanwhile, note that there have been multiple studies suggesting testosterone can increase risks of cardiovascular issues; in 2015 the FDA mandated that testosterone supplements be clearly labeled for use only in clinically low T cases and include information about these potential risks. Critics also note that high T levels may suppress the immune system and increase risk-taking behaviors. Testosterone, argues Richard Wassersug, an evolutionary biologist who works at the University of British Columbia and Australia's La Trobe University, "puts us in contest with other males in ways that can increase our chances of getting our genes into the next generation [but can also] get us killed." Then there are historical studies of eunuchs—one on castrated inmates at a Kansas mental institution in the 20th century and one on Korean court eunuchs in the Chosun dynasty—suggesting that men without testicles and the testosterone they make live consistently and significantly longer than their peers in similar conditions. A few animal castration studies seem to support this notion as well, and there've long been theories that different T levels explain at least some of the global phenomenon of longer female lifespans.
Morgentaler argues that there are serious flaws in studies showing cardiovascular risks tied to higher testosterone levels, evolutionary biological arguments are theoretical at best, and historical eunuch studies (some of which point in the opposite direction) had effectively no control groups. Morgentaler believes T has developed a bad reputation over the years (due to its use by cheating athletes and the like) that has blinded opponents to its potential benefits. Opponents, meanwhile, argue there are better-proven and more effective therapies for most of the symptoms T treatments aim to address. And even if T treatments can help people with clinically low T levels, that's a tiny population (although some drug companies claim it's an under-diagnosed condition), and low T is actually hard to measure, ill defined, perhaps even fully idiosyncratic.
"There is no [clear] evidence that testosterone has any documented influence on human longevity," concludes Stuart Jay Olshansky, an expert on aging at the University of Illinois at Chicago, "either positive or negative."
It's hard for anyone to rule definitively on either camp's evidence and interpretations because even the recent T Trials were limited in size and scope. Experts agree on the need for massive, long-term, randomized trials—ideally involving varied forms and methods of applying T treatments. But as hormone specialist and University of Washington professor Bradley Anawalt points out, such studies would be expensive (one scientist recently suggested a hypothetical five-year, 5,000-man, $500 million study). They would also likely be difficult to organize—especially if one wanted to review the effect of T treatments on men with normal testosterone to reflect the fact that individuals like that are already reportedly utilizing T treatments.
Even if there were such a study, it might not come down decisively on one side of the debate because T may not have solid positive or negative effects on health and longevity. "Testosterone … is a social molecule with a single purpose," Wassersug says, "to make sure our genes get into the next generation. This whole conversation about testosterone and longevity is really quirky and unnatural," as fighting aging and helping our health isn't its clear biological function.
All of which leads to the very unsatisfying conclusion that a testosterone booster may be good for your health and lifespan, but we don't know enough to say for sure one way or another and no one will be handing down a smoking gun on the issue anytime soon. As such, if you get tested, learn you have clinically low testosterone, and your doctor recommends you take a treatment to get back to normal, that's probably a good idea—something is likely up with your hormonal balance and probably your total body and wellbeing that needs addressing. But if you're just on the hunt for a little more pep in your step (as a good chunk of the T market appears to be today—perhaps believing their low pep-in-step levels are due to undiagnosed low T levels) then T's probably not for you. The standard mantra of a better diet, exercise, and general lifestyle probably is right for you—even if that's not what most men want to hear.