Trouble getting pregnant, fatigue, erectile dysfunction, and hair loss are all common symptoms of low testosterone. Ads from a booming testosterone industry remind us of this constantly, as do food and fitness “hacks” touted by so many influencers. Professional opinions on the right levels of testosterone for men vary widely — even among tenured experts. No wonder so many men obsess over their testosterone levels. A new study aims to clear up what can be defined as low T — by outlining the differences in testosterone through age. But some doctors wonder whether the proposed change could throw tens of millions of men into even more confusion over where they stand and what to do about their testosterone.
Getting To A New Testosterone Threshold
The new study, published in The Journal of Urology, argues that the standard cutoff point for clinically low testosterone levels in men needs to be adjusted. There’s currently a single cutoff for low blood testosterone: 300 nanograms per deciliter (ng/dL). But the study researchers argue that what counts as low T depends on a man’s age — an aspect previously overlooked because most data collected came from men over 40.
“Young men have different testosterone reference ranges than older men,” said lead author Alex Zhu, D.O., a urology resident at Michigan Medicine, in a press statement. “Our findings suggest we should be using age-specific cutoffs when assessing testosterone levels in younger men.”
How much testosterone a cisgender man has in his body — measured through a blood test — can change throughout his lifetime, and most start experiencing a decline around age 30 to 40 as the glands that produce testosterone, including those in the testicles, start slowing down. Testosterone levels also drop when a man becomes a dad, which may have an evolutionary root in the dad giving up hunting for new mates and instead becoming a family man, increasing the survival of his baby.
Before that decline begins, “normal” testosterone levels range from about 264 ng/dL to 916 ng/dL, according to the Endocrine Society. But different studies over the years have yielded slightly varying results of what normal ranges can be.
To learn more about normal testosterone levels throughout a man’s lifetime, Zhu’s team analyzed testosterone data from nearly 1,500 U.S. men between the ages of 20 and 44. For each age group, they split up the testosterone levels they found into thirds: a low third of the population, an average third, and a high third. They found that with every year a man gets older, his testosterone drops by an average 4.3 ng/dL.
The researchers found that a testosterone level anywhere below 409 ng/dL — well above the current low testosterone cutoff — is already low for a man in his early 20s compared to the average T levels of his 20- to 24-year-old peers. This calls for an update to low testosterone standards, Zhu’s team argues, and that man should be considered to have low T and be eligible for insurance-covered testosterone therapy.
The Argument For Age-Specific Testosterone Cut-Offs
With these findings, clinicians could use age-specific low T cutoffs instead of a “one size fit all” approach, according to Zhu’s team. Changing the official thresholds used by doctors — like the one set by the American Urological Association Testosterone Deficiency guidelines, which came out in 2018 and probably won’t get updated for a few more years — could make it easier for younger men who may need it to access testosterone therapy. Currently, insurance only tends to cover patients who fall below the standard 300 ng/dL cutoff.
But having lower testosterone than your peers — specifically, falling into the lower third of testosterone levels for your age group — doesn’t necessarily mean you’ll have symptoms of low testosterone or need treatment, says Kevin Campbell, M.D.,a urologist at the University of Florida Health who was not involved in the study. Not everyone under 300 ng/dL has symptoms that can be traced back to low T, and not everyone above that level is symptom-free.
“We do have to take it with a grain of salt,” says Campbell. Testosterone, like everything in the body, operates in a complex system — although blood levels of testosterone can be high or low, the amount of T actually available to the body might be different, because testosterone is bound to other molecules that orchestrate whether testosterone is used or not.
“The concept of age-appropriate thresholds for testosterone deficiency makes a lot of sense,” says Guillaume Paré, M.D, a molecular epidemiologist at McMaster University in Ontario, Canada, who was not involved in the study. Paré does, however, worry that testosterone deficiency is too often defined as testosterone concentration below the 33rd percentile, basically saying that one in three men will always be testosterone-deficient. He doesn’t think that’s reasonable.
“By design, current thresholds categorize a third of males as having low testosterone. This is a large proportion of individuals and might not reflect whether biologically there is too little testosterone,” says Parè.
The Risks And Rewards Of Testosterone Treatment
He believes that there should be stricter thresholds for low testosterone, and worries that a diagnosis of testosterone deficiency at a young age could lead to overzealous long-term treatment with testosterone replacement therapy, of which the potential side effects are yet to be researched in detail.
“The potential side effects of such treatment are not well understood,” Parè says. “Our own research suggests it could lead to an increased risk of prostate cancer, high blood pressure, and baldness,” he says, pointing to his 2020 study in the journal eLife.
The FDA has issued warnings that testosterone therapies can increase the risk of heart failure. However, its European equivalent, the EMA, notes that the data doesn’t sufficiently support that testosterone therapy causes heart problems. The scientific jury is still out on other effects of the therapy, including whether it betters or worsens sleep apnea, for example.
A 2022 study by Northwestern Medicine suggests that commercial brands providing testosterone therapy are quick to provide medication without going through its pros and cons — for example, 83.3% of the surveyed brands did not mention the possibility of an increase in blood thickness.
“We should make sure there is a clear benefit to each patient started on testosterone replacement therapy, as it might not be as benign as sometimes assumed,” Parè says
To avoid unnecessary treatment, it’s important not to interpret testosterone levels in isolation, says Richard Anderson, Ph.D., M.D., co-director of the Centre for Reproductive Health at The University of Edinburgh in Scotland, who wasn’t involved in the study. Whether the man is experiencing symptoms, has other health issues, has been under recent stress, or has experienced any lifestyle changes that could affect his testosterone levels, such as increased smoking or drinking, is imperative for interpreting testosterone blood levels in context.
Sometimes patients are able to wean off of testosterone replacement therapy, though they would likely have all the same symptoms that first brought them to therapy. And stopping high-dose testosterone therapy can cause drastic withdrawal symptoms.
“We know of the consequences of very low levels, and it is clear that treatment is beneficial,” says Anderson. “But this is not the case for less marked low levels, and we must avoid over-treatment, as it’s very difficult to stop treatment later.”
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