Why Testosterone Declines With Age (And What You Should Do About It)

If you want to avoid testosterone decline with age, you need to understand something most men don't: not all testosterone decline is created equal.

Age-related testosterone decline is either a sign that something is wrong with your health, or your body executing a process that may actually be keeping you alive longer.

If you miss that distinction, you'll either panic about a decline that's completely normal, or ignore the one that's actually a problem.

Before we dive in, some important context is in order.

This article is part 3 of my series on testosterone decline with age. In parts 1 and 2 we established that:

Total testosterone levels remain stable across the lifespan in healthy men (defined as having no chronic diseases).
Free testosterone declines in all men, although to a lesser extent in healthy men.

This begs the question; if total testosterone levels can be maintained with good health, then why does free testosterone still decline?

This question is important to answer because free testosterone is the version of testosterone that's actually capable of exerting effects in the body.

So even if a man's total testosterone levels are maintained, if free testosterone drops too low, then symptoms of low testosterone can still arise.

To understand the mystery of free testosterone decline, you need to understand why anything would reduce testosterone levels.

To understand that, you need to understand…

How Testosterone is Produced

There are three glands involved in testosterone production:

The hypothalamus (in the brain).
The pituitary (also in the brain).
The gonads, aka testes (you know where those are).

All three of these glands (referred to as the HPG Axis) work together to produce testosterone. Here's how:

The hypothalamus secretes gonadotropin releasing hormone (GnRH), which tells the pituitary to secrete luteinizing hormone (LH), which tells the testes to produce testosterone.

Therefore, anything that damages any of these glands disrupts testosterone production.

In biology, the primary driver of cellular damage is a process called oxidative stress, which is often the common denominator behind how modern lifestyle factors disrupt the HPG axis (1).

Oxidative stress has many causes: poor metabolic health, chemical exposure, smoking, improper sleep, psychological stress, etc (1).

Just about anything that is "unhealthy" or "bad" for you causes oxidative stress, but the underlying mechanism is always the same.

All you really need to know is that oxidative stress occurs as a result of an imbalance between excessive free radicals and insufficient antioxidants (1). Free radicals "steal" electrons from the atoms that make up the cells in your body, which destabilizes the cells and causes damage (1).

You can think of oxidative stress like rust on a car. Rust has many causes: salt, water, mud, sunlight, etc, and excessive rust can cause different parts of the car to stop working properly.

Just like rust on a car, the accumulation of oxidative stress causes different systems in the body to stop functioning properly, including the HPG axis.

In this way, oxidative stress to the HPG axis leads to decreased testosterone production.

Oxidative stress → Hypothalamus → Reduced GnRH Secretion (2)
Oxidative stress → Pituitary → Dysregulated LH Pulsatility (3)
Oxidative stress → Gonads (Testes) → Less Responsive to LH (2)

This model is supported by studies showing a direct inverse relationship between testosterone levels and oxidative stress (13). In other words, more oxidative stress equals lower testosterone levels.

The good news is that most causes of oxidative stress are avoidable. We can all exercise, eat healthy, sleep well, and manage our stress.

But there's one cause that no man can escape.

Oxidative stress also happens to be a natural byproduct of normal cellular functioning, called cellular respiration (aka "cell breathing") (14).

This means that living itself causes some oxidative stress, so a continuous trickle of oxidative stress over time is inevitable.

Simply put: aging causes some oxidative stress.

But any oxidative stress beyond aging (and a few other natural bodily processes) damages the body unnecessarily.

This explains why testosterone declines faster in "unhealthy" men than in "healthy" men. Since unhealthy men accumulate more oxidative stress, they are biologically "older" than healthy men of the same chronological age (14).

To be clear, health isn't binary; you aren't just "healthy" or "unhealthy." Health is a spectrum; the less unnecessary oxidative stress you accumulate, the slower you'll age, and the higher your testosterone levels will be, consistent with research confirming that testosterone is an effective barometer of overall health (15).

That said, no man can completely avoid the natural oxidative stress that inevitably comes with age, which is why research shows some degree of HPG axis dysfunction with age, including in healthy men.

Age-related oxidative stress to the hypothalamus causes GnRH production to decrease, and also causes the testes to become less responsive to LH signals telling them to produce testosterone (3).

Nonetheless, healthy men still maintain their total testosterone levels until very late in life.

How is this possible?

Wouldn't less GnRH from the hypothalamus lead to less LH from the pituitary?

And wouldn't less responsive testes lead to less testosterone production?

The body has a clever workaround…

How Healthy Men Maintain Normal Total Testosterone Levels With Age

The pituitary seems to compensate by secreting more LH to get the testes to produce testosterone at a normal level (3).

It's sort of like how, when talking to older folks who are hard of hearing, you have to speak the same words (LH) at a louder volume (higher levels) to communicate the same message (produce testosterone).

Reduced Testosterone Turnover

While elevated LH helps maintain total testosterone production, the other mechanism through which testosterone levels are maintained involves preserving testosterone after it is produced.

Think of testosterone production like a business. There are two ways a business can increase profit:

Generating more revenue (making more money).
Reducing expenses (spending less money).

Likewise, there are two ways the body can increase circulating testosterone levels:

More testosterone in (through increased LH production).
Less testosterone out (by breaking down & excreting less).

Just like how generating more revenue isn't the only way a business can increase profit, producing more testosterone isn't the only way the body can elevate testosterone levels.

The body can also "reduce its expenses" by slowing the rate of testosterone turnover; the process through which testosterone is metabolized (broken down) after it's been produced.

The speed at which testosterone turnover occurs is called the "apparent metabolic clearance rate of testosterone" (aMCR-T).

Studies show that aMCR-T is approximately 24-33% slower in older men than younger men (4), meaning once testosterone is produced, it "stays alive" for longer before being broken down.

This appears to be another compensatory mechanism to maintain normal testosterone levels. Since older men can't produce quite as much testosterone on the front end, their bodies tend to hold on to the testosterone they do produce for longer.

The final picture of testosterone in aging men looks like a business in a recession. Since the body can't produce testosterone (make money) as well, it dials back testosterone turnover (reduces expenses), with the net result being that total testosterone levels (profit margins) are maintained.

Increased DHT Conversion — The Cause of "Old Man Strength?"

The third way in which healthy men maintain their overall androgenic status is by increasing DHT production ("androgenic" refers to the total effect of all androgens, or testosterone derivatives, in the body).

You can think of DHT as testosterone on steroids. DHT has a much higher binding affinity for androgen receptors — the sites on cells where any androgen can bind and exert their effects.

DHT exerts similar effects as testosterone, but it does so much more profoundly.

Two studies show that DHT increases moderately with age (6)(7).

This appears to be another compensatory mechanism through which the body attempts to maintain its overall androgenic status with age.

Since DHT is mostly created through the breakdown of free testosterone, increased DHT production necessarily decreases free testosterone levels, which is one reason why free testosterone declines with age (we'll unpack the second reason shortly).

The rationale for increased DHT production is as follows. The body thinks "okay, I have less free testosterone to work with, so I'm going to turn more of it into DHT so I can get the same effect with less raw material."

It would be like a military investing more money into missiles (DHT) as opposed to assault rifles (testosterone). With less overall funding, more damage can be done with missiles than assault rifles.

The fact that the body goes through such a valiant effort to maintain its androgenic status (by upregulating LH, downregulating testosterone turnover, and increasing DHT production) would seem to suggest that it "wants" to keep testosterone levels up throughout life.

But the story doesn't end there. Yet again, another paradox emerges…

The Paradox of Free Testosterone Decline

Even though the body works so hard to maintain total testosterone production, free testosterone still declines ~2% per year starting around middle age (8).

The net result is that the reservoir of total testosterone remains just about full, but a smaller proportion is available for immediate use.

Although some free testosterone is broken down and converted into DHT, this only explains a tiny fraction of free testosterone decline.

The main reason why free testosterone declines with age is because SHBG levels rise. SHBG is the protein that binds to naked testosterone and keeps it inactive until it's released.

The inverse correlation between free testosterone levels going down and SHBG levels going up is almost perfectly proportional (9).

Notably, rises in SHBG and concurrent declines in free testosterone are observed across all populations; including healthy men from industrialized nations (8), and men from subsistence populations (10) whose lifestyles emulate those of our pre-modern ancestors.

This is important to point out because it suggests that free testosterone decline is an intrinsic part of natural aging, not a byproduct of poor health or an artifact of modern living.

To be clear, just because free testosterone declines with age does not mean you're condemned to a hypogonadal state (having symptoms of clinically low testosterone).

In fact, there are countless cases of men who maintain an abundance of energy, fertility, and fitness well past middle age, completely naturally.

You probably know guys like this in your personal life: like the father of three doing muscle ups at the park with his kids. Or your fifty year old co-worker who still participates in Jiu-Jitsu competitions.

The most dangerous thing you can do is start blaming age for any signs of low testosterone you may be experiencing (part 2).

You may not be able to bench press quite as much as you could in your twenties, but if you don't look and feel great throughout your life, it's because something is off with your health or lifestyle, not because of age.

With that out of the way, the final picture of androgenic status in healthy aging men raises a critical question:

Why would the body go through all the effort to maintain total testosterone levels, just to bind up more of it with SHBG? Put another way, why does SHBG increase with age?

Why Does SHBG Increase With Age?

SHBG increases with age primarily because the production of growth hormone (GH) from the HPS axis (hypothalamic–pituitary–somatotropic axis) decreases (12).

Growth hormone is a potent suppressor of SHBG, so declines in growth hormone result in increased SHBG production from the liver (12).

Here's the overarching process from start to finish:

GHRH release from the hypothalamus declines → GH production from the pituitary declines → the brake on SHBG production is released → SHBG rises → more free testosterone gets bound up → less free testosterone is available.

This entire hormonal cascade is called somatopause ("somato" = body, "pause" = cessation) (11).

You can think of somatopause like reverse puberty. Puberty encourages growth and reproduction, whereas somatopause prioritizes life extension at the expense of growth and reproduction.

This is why the same hormones that rise during puberty (growth hormone and free testosterone) fall during somatopause (11).

Tracing somatopause back to the root, you can see that declines in growth hormone originate with decreased functionality of the hypothalamus — the same conductor of the HPG axis that produces total testosterone.

Unlike the HPG axis, the HPS axis does not have mechanisms in place to compensate for reduced hypothalamic functioning, which is why total testosterone can be maintained with age, but growth hormone, and subsequently, free testosterone, cannot.

And as we established, the primary cause of most cellular damage is oxidative stress. Thus, oxidative stress to the hypothalamus appears to be the root cause of somatopause.

An individual's total oxidative stress levels are the combination of the necessary oxidative stress accumulated from normal aging, plus all of the unnecessary oxidative stress accumulated from poor health and other factors.

Since an individual's total oxidative stress levels are a key determinant of biological age (14), it is your biological age that determines both when your free testosterone levels will decline and the magnitude of those declines, not the number of years you've been alive (5).

So the more oxidative stress you accumulate relative to your chronological age, the sooner and faster your free testosterone levels will decline.

By analogy, a well-maintained car (healthy man) can operate better at 100k miles (age 45) than a poorly maintained car (unhealthy man) also at 100k miles (age 45).

The two different causes of oxidative stress require different responses on your end.

Oxidative Stress From Poor Health

Anything that damages your physical or mental health causes unnecessary oxidative stress ("unnecessary" meaning all sources of oxidative stress that are not natural byproducts of normal cellular aging).

Therefore, your goal should be to eliminate as much unnecessary oxidative stress as possible by living a holistically healthy lifestyle.

Although it sounds simple, doing so in the modern world can be quite challenging because we live in an evolutionarily mismatched environment. Factors like sedentary jobs, processed food, and environmental toxins add to our oxidative stress levels from all angles.

But there is cause for hope because managing such factors is completely within your control. By implementing proper lifestyle changes, you can effectively negate most modifiable risk factors.

Not only that, but the effects of modifiable risk factors on biological aging and testosterone decline are much greater than natural aging.

One study found that becoming obese decreased total testosterone levels as much as 10 years of aging (8). In other words, you can keep your testosterone levels 10 years "younger" just by maintaining a healthy weight.

So if you aren't already doing everything in your power to optimize your physical and mental health, start now. I unpack everything you need to know about how to do that in part 5 of this series.

The second cause of oxidative stress demands a different approach…

Oxidative Stress From Cellular Respiration (Aging)

Even if you lived a perfectly healthy lifestyle from the moment you were born, the slow trickle of oxidative stress from natural aging would eventually lead to the initiation of somatopause; modest declines in growth hormone and free testosterone starting sometime around middle age (11).

Since this age-induced oxidative stress is out of your control, the proper response to it involves a new disposition, which is best summarized by a quote from the great Marcus Aurelius: "acceptance without disdain."

That said, it's crucial not to disguise complacency as acceptance. All too often, men use age as a scapegoat for their problems instead of taking responsibility for them (part 2).

Sure, it may not be quite as easy to put on muscle at 55 as it was at 25, but blaming the dad bod on aging when you skip the gym and have pizza for dinner is unacceptable.

On the flip side, if you're already doing everything in your power to optimize your health, it's equally important to willingly embrace natural aging without resistance. Mentally resisting aging is futile; no amount of fighting it in your head will stop it, and may even accelerate aging by unnecessarily stressing yourself out.

As a man, I totally understand how it might be hard to accept some of the effects of somatopause; less muscle mass, lower libido, etc.

But when you have a complete understanding of the purpose of somatopause in both individual men and collective populations in the context of human evolution, it becomes evident that somatopause wasn't programmed to emasculate you, but rather to extend your lifespan and the continuation of our species.

Understanding this enables you to view the changes that come with somatopause as fair tradeoffs rather than purely negative side effects. From that perspective, accepting somatopause becomes much easier, and gives you peace of mind that you otherwise wouldn't have. We take a deep dive into why somatopause is actually beneficial in part 4 of this series.

From this article alone, you now understand what most men don't: although some degree of free testosterone decline is inevitable, a hypogonadal state is not. As long as you keep free testosterone decline to its natural minimum, you can expect to retain plenty of vitality until the day you die. To do that, you need to be doing everything in your power to optimize all aspects of your physical and mental health.

If you'd like professional assistance with that, I strongly encourage you to look into the Testosterone Transformation Academy, where we install evidence-based protocols designed to optimize your testosterone levels into your life through personalized coaching.

Optimize Your Testosterone levels Naturally In The Testosterone Transformation Academy

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