For years, researchers have observed a troubling trend: testosterone levels in men seem to be declining across generations. This hormone, crucial for male health, has been linked to energy, mood, muscle mass, and even heart health. But a new study is challenging what we thought we knew — suggesting the supposed decline may be based on a surprising technical detail.
In this article, we’ll dive into the science, explore global trends, and unpack what might really be going on with men’s testosterone levels.
Table of Contents
- Testosterone Is Declining — Or Is It?
- Global Evidence of Falling T
- The Obesity Explanation
- The New Study That Changes Everything
- How to Raise Testosterone Naturally
- So, What Can You Do?
- References
Testosterone Is Declining — Or Is It?
2007 was a turbulent year.
On one hand, it was the year the iPhone launched. We were all finally able to put the addictive power of social media in the palms of our hands and wreck childhood for millions across the globe.
On the other hand, there was some shocking news that came from a study published in one of the most respected journals dealing with hormone-related issues.
Researchers had gathered blood samples from about 1,500 men at three different times between 1987 and 2004. The purpose? To see what was happening to testosterone levels through time [1].
Data obtained from 1,374, 906, and 489 men at T1, T2, and T3 respectively — totaling 2,769 observations taken on 1,532 men.
Testosterone naturally drops as we age. In men, after we hit 30, levels decrease by about 1–2% a year on average [2]. This pattern is well established, and it isn’t necessarily a problem. It’s just part of getting older.
But there was some evidence that something else might be going on. Not only were testosterone levels declining with age, but it appeared they might be declining with each new generation as well [1].
It appeared something in our environment might be attacking testosterone, driving down levels.
And this isn’t just a matter of low sperm counts and poor sexual function. Low testosterone also weakens bones, decreases energy, and depresses mood [3]. It’s also linked with elevated all-cause and heart-disease-related mortality [4].
Researchers were compelled to figure out if this testosterone decline was real, and if so, what was causing it.
Global Evidence of Falling T
They started by looking at what was happening to testosterone levels outside the USA.
A large population study in Denmark also uncovered falling levels [5]. And so did a study in Finland [6]. A more recent study, again in the U.S., found that the trend continues [7].
“TT levels were lower in the later (2011–2016) than in the earlier (1999–2000) cycles (all p < 0.001).”
So far then, we have multiple different studies in different countries suggesting that testosterone levels are indeed falling. It’s a worldwide issue.
The Obesity Explanation
But here’s the real puzzler. Why on earth is this happening? It’s been a huge matter of debate.
There’s been no lack of ideas about potential causes. Some have suggested it’s all those pesticides we’re getting in modern diets [8].
Then there’s microplastics, which have been shown to reduce testosterone levels in mice [9].
Or maybe it’s aluminum [10].
But most of the proposals fail to actually explain the data. On the other hand, one important causal factor has emerged: obesity. But even obesity didn’t explain the full picture, as we’ll see.
Excess weight triggers testosterone reduction through processes related to insulin resistance and other mechanisms. And the problem is, low testosterone by itself leads to weight gain. So there’s a negative feedback loop [11].
“Low testosterone by itself leads to increasing adiposity, creating a self-perpetuating cycle of metabolic complications.”
Worldwide, the rate of obesity is increasing. In adults, it has more than doubled since 1990. For adolescents, it has quadrupled [12].
Given obesity’s negative impact on testosterone levels, it seems like this might explain the trend. In the study from Denmark, for instance, the pattern of falling testosterone went away when they took rising obesity into account [5].
But the mystery isn’t solved just yet. A ballooning obesity rate doesn’t seem to tell the whole story.
To see why, we need to look at a recent study from Israel. Researchers analyzed the testosterone levels found in tests that were given to over 100,000 men between 2006 and 2019 [13]. In line with the trend we’ve been talking about, they also saw a population-wide fall in testosterone levels [13].
But there was something interesting in the data. When they looked at BMI, they didn’t see an increase across the timeframe included in the study. That means the drop in testosterone levels couldn’t be solely explained by rising obesity [13].
Researchers concluded something similar in the most recent U.S. study. They found a decline in testosterone even among men with normal BMI [7].
The New Study That Changes Everything
So what else might explain the decline in testosterone in Israel and elsewhere? A new analysis gives us a completely unexpected answer.
The authors of the analysis were interested in a key issue lying in the background of the discussion about falling testosterone. And that issue concerns how testosterone levels are measured.
This has actually been highlighted before. Researchers behind a 2020 study noted there is a potential problem lurking here. After reporting that testosterone levels are declining, they include an important qualification: the data they rely upon includes different methods for measuring testosterone levels [7].
Why might this be an issue? Well, different measurement methods can give different answers.
Suppose I had to take a flight and crammed everything I needed into a carry-on bag. At home, I weighed it — just under the 10 kg limit. But when I got to the airport, the airline’s scale said 11 kg. Now, here’s what I wouldn’t do: I wouldn’t call my wife and say, “Honey, you won’t believe what happened. My bag gained a kilo while I was on the way to the airport!”
You get the point. Measurement method matters. When we use different tools, any differences we see might simply be due to the methods used.
So now you can see the intriguing possibility. When it comes to testosterone, are our measurement methods distorting the true picture of what’s going on?
That’s what the authors of this new study wanted to find out. They explored U.S. health data from five distinct time periods [14].
This same dataset has been used in prior studies to show that testosterone is falling [7].
But here’s the twist: The first two time periods used one method of measurement, while the latter three used an entirely different method [14].
The 2 earliest cycles used the Roche Elecsys immunoassay, whereas the later cycles (2011 onward) used an LC-MS/MS assay.
The newer method tends to give lower readings.
So when we plot the five time periods individually on a graph, with the bars representing the share of men with low testosterone — and the colors representing testing methods — we see a huge jump in low testosterone that coincides with the change in measurement method [14].
“The marked increase in the fraction of healthy males with TT < 300 ng/dL from 2004 (12%) to 2011 (22%) coincides with the migration from immunoassay to LC-MS/MS.”
The implications are huge. That trend of falling testosterone? It might be just because we’re measuring it differently.
The authors argue we need a new threshold to reflect the new methods. When we make that adjustment, the percentage of men with low testosterone stays flat — or even declines [14].
“This suggests that the Endocrine Society’s proposed low cutoff of 264 ng/dL may be a more accurate threshold going forward, than the historically used 300 ng/dL.”
This completely upends the narrative. Testosterone levels might not be falling at all. In fact, over the last three measurement periods, the percentage of men with low testosterone is actually falling.
So this might just be the answer to why testosterone levels are falling: They aren’t.
But we need to back up for a moment. Because the authors here are looking at U.S. data. If we return to that Israeli study, this way of accounting for the decline in testosterone doesn’t apply.
Why not? Because the authors explicitly state that the testing methodology was the same throughout the data collection period [13]. Just one “scale.” Yet they still saw a decline.
“All the samples were measured using the same lab methods... at a single central lab.”
But there’s a crucial issue with the methodology that raises a big question mark.
The men included in the study had their testosterone tested because they were referred by a physician [13]. In other words, their doctor suspected a problem.
Why might this be an issue? Because we’re going to end up just testing men where there was already concern about low testosterone. So it’s not a true representation of the general population.
So there’s at least a question mark when it comes to that study in Israel.
But the big takeaway is this: The thesis that testosterone is falling is at least in doubt. We may soon come to realize the whole panic has been based on a simple problem with how we’ve been measuring it.
How to Raise Testosterone Naturally
Whatever the real story turns out to be, we do know that — individually — testosterone declines with age. Even if we aren’t clinically low, it makes sense to try to counter this natural decline.
1. Lose Excess Weight
If we’re overweight, the most significant thing we can do is decrease our body fat. Obesity is strongly linked to lower testosterone levels in men [15]. A recent review of the literature identified weight loss as the first-line intervention to boost testosterone in obese men [15].
In addition to diet and exercise, medications such as Tirzepatide can help patients with their weight loss journey.
2. Exercise — Resistance and Aerobic
Scientists have discovered that resistance exercise elevates testosterone [16].
Specifically, multi-joint movements, high volume, moderate to high intensity, and short rest periods may result in optimal acute increases in serum testosterone levels.
Aerobic training has also been shown to moderately increase testosterone levels in men with obesity or type 2 diabetes [17].
3. Prioritize Sleep
Testosterone levels peak during sleep. Researchers have speculated that getting too little sleep could suppress levels [18].
One small study had participants cut sleep to just 5 hours a night for 8 nights [19]. Testosterone levels were significantly lower during this sleep-restricted period.
A meta-analysis confirmed that sleep duration plays a pivotal role in maintaining testosterone [18].
4. Consider TMG Supplementation
My patients sometimes ask me about supplements. There are some out there with study evidence to back them up. One is Betaine — or TMG.
A study with soccer players supplementing with TMG found increases in testosterone over a season [20].
Another study had participants follow an exercise regimen while supplementing with TMG. Resting testosterone levels significantly increased compared to placebo [21].
This research is one of the reasons I take TMG as part of MicroVitamin. But just because I take a supplement, that doesn’t mean you need to, too.
So, What Can You Do?
To support healthy testosterone levels, consider these four strategies:
- Lose weight if overweight
- Exercise regularly, focusing on resistance and aerobic training
- Get adequate sleep
- Optionally, explore TMG supplements
References
1. https://pubmed.ncbi.nlm.nih.gov/17062768/
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC6966696/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC10338218/
4. https://pubmed.ncbi.nlm.nih.gov/25269643/
5. https://pubmed.ncbi.nlm.nih.gov/17895324/
6. https://pubmed.ncbi.nlm.nih.gov/23161753/
7. https://pubmed.ncbi.nlm.nih.gov/32081788/
8. https://www.scientificamerican.com/article/pesticides-may-block-male-hormones/
9. https://www.mdpi.com/2305-6304/12/8/561
10. https://www.sciencedirect.com/science/article/abs/pii/S002432052400050X
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC3955331/
12. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
13. https://rbej.biomedcentral.com/articles/10.1186/s12958-020-00575-2
14. https://academic.oup.com/clinchem/article-abstract/71/5/609/8114673
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC11745839/
16. https://pmc.ncbi.nlm.nih.gov/articles/PMC7739287/
17. https://pmc.ncbi.nlm.nih.gov/articles/PMC11519272/
18. https://www.sciencedirect.com/science/article/abs/pii/S138994572100544X
19. https://pmc.ncbi.nlm.nih.gov/articles/PMC4445839/
20. https://pmc.ncbi.nlm.nih.gov/articles/PMC7934563/
21. https://pmc.ncbi.nlm.nih.gov/articles/PMC9116406/
