Why your testosterone drops after 35

Almost every man who came to my practice asking about his testosterone brought the same sentence: "I guess it's my age." And age does matter. But in the years I practiced urology, when the workup was done properly, age was almost never the only thing going on.

This article lays out what we know: which part of the decline is normal physiology, which part is reversible, and what has to be measured before making any decision.

The part that really is age

Clinical consensus. From about age 30 or 35, a man's total testosterone falls on average by roughly 1 % per year. It is a slow, progressive decline, not a drop.

There is a detail almost nobody explains, and it changes how everything is read: free testosterone falls faster than total testosterone. With age, SHBG rises, the protein that carries testosterone in the blood. The more SHBG, the more hormone is "bound" and the less remains available to the tissues. That is why some men have an apparently normal total testosterone and a clearly low free testosterone.

In plain terms: one number, on its own, tells you almost nothing.

Why a single result misleads

Clinical consensus. Testosterone has a circadian rhythm: it is highest in the morning and falls through the day. That is why guidelines ask for the sample fasting and early, ideally between 7 and 10 a.m., and repeated on a second day before concluding anything.

On top of that, the value drops temporarily in situations that have nothing to do with your testicles:

• a recent infection or acute illness
• a week of poor sleep
• a period of intense stress or overtraining
• an aggressive calorie deficit
• heavy alcohol intake in the preceding days

Getting your testosterone drawn on Monday at four in the afternoon, after a weekend of little sleep and alcohol, and drawing conclusions from that, was the most common mistake I saw.

The accelerators that are not age

This is the important part, and it is where something can be done.

Visceral fat

Clinical consensus. Fat tissue contains aromatase, the enzyme that converts testosterone into estrogen. More abdominal fat means more conversion, less available testosterone and, at the same time, more insulin resistance, which worsens the picture. It is a loop: low testosterone makes it easier to gain fat, and the fat gained lowers testosterone further.

Sleep apnea

Clinical consensus. Obstructive sleep apnea is one of the most overlooked treatable causes in men aged 35 to 55. It fragments deep sleep, which is precisely when most of the night-time testosterone secretion happens. If you snore, if you wake up tired, if your partner describes pauses in your breathing, that gets studied before anyone talks about hormones.

Chronically short sleep

Clinical consensus. A classic study published in JAMA in 2011 restricted the sleep of young, healthy men to five hours a night for one week: daytime testosterone fell by 10 to 15 %. One week. In healthy men.

If you have been sleeping six hours for years, that cost is not theoretical.

Medications and substances

Clinical consensus. Opioids and glucocorticoids suppress the hormonal axis directly, and this is well documented. So does sustained alcohol intake. Some hair-loss treatments, certain antidepressants and a number of other drugs have effects on sexual function and hormones that are worth reviewing with whoever prescribed them.

What gets measured, and why

Clinical consensus. A serious male hormone workup is not "getting your testosterone checked." At a minimum it includes:

• Total testosterone, morning and fasting, confirmed in a second sample
• SHBG and albumin, to calculate free testosterone
• LH and FSH, which say where the problem is
• Prolactin, especially if testosterone is low and LH is not high
• Estradiol
• Hematocrit and hemoglobin
• Glucose, HbA1c and lipid profile
• TSH
• Ferritin, which can reveal iron overload
• PSA, depending on age and risk

The LH–testosterone pair is what organizes the diagnosis:

• Low testosterone with high LH points to the testicle: the brain is asking and the testicle is not responding.
• Low testosterone with normal or low LH points upstream, to the hypothalamic-pituitary axis. That is where obesity, sleep apnea, chronic stress, drugs, and less frequent but important causes such as a pituitary adenoma or hemochromatosis come in.

These are two different scenarios, with different tests and different routes. That is why it matters to measure properly before treating.

What gets corrected first

Clinical consensus. Before any hormone therapy, there are five fronts that change the result in a measurable way:

1. Body composition. Losing visceral fat raises testosterone. That is not a marketing promise: it is aromatase.
2. Sleep. Seven to nine hours, with an apnea study if there are signs.
3. Strength. Progressive resistance training, with real recovery between sessions.
4. Alcohol. Actually cutting back, not just "moderating" on paper.
5. Reviewing medications, with the doctor who prescribed them.

In quite a few men, especially those who arrive overweight and sleeping badly, this alone changes the picture, and the conversation about hormone therapy stops being urgent.

When hormone therapy is justified, and when it is a shortcut

Clinical consensus. Testosterone therapy is considered when there are compatible symptoms and low values confirmed in two morning measurements, with secondary causes studied. The American Urological Association guidelines (2018) use 300 ng/dL as a reference; the Endocrine Society works with 264 ng/dL. These are reference cut-offs, not magic borders: a man at 310 with clear symptoms and another at 290 without symptoms are not the same case.

There is one point I want to make very clear, because it is rarely explained and has serious consequences:

Exogenous testosterone suppresses sperm production. If you are trying for a pregnancy, or might be, that is a conversation to have before starting, not after.

My clinical opinion. The shortcut that does the most harm is not hormone therapy that is properly indicated and properly monitored. It is therapy started without a complete workup, without a diagnosis of the cause, without talking about fertility and without follow-up. That is not optimization: it is covering a symptom and losing the information that was underneath it.

What I'd like you to take away

Age explains part of the decline. Your sleep, your visceral fat, your alcohol, your medications and the illnesses nobody has looked for yet explain, in most of the men I treated, quite a bit more.

Being tired is not normal. It's a signal. And a signal gets studied before it gets silenced.

The author is the founder and CEO of Mengenics, a men's health clinical platform. This article is educational and does not promote any treatment.