Written by
Louise W Lu, PhD, MPH, BMLS
Written/Reviewed by
Michelle Ordner, Registered Nurse
One of my students asked:
“I've noticed my energy levels have significantly decreased lately. I used to work out and run effortlessly, but now even a short exercise leaves me exhausted. I'm also struggling to focus at work and having trouble sleeping. But I'm only in my early 40s—is this normal?”
In fact, this is a common issue faced by many men over the age of 40, yet it is frequently overlooked or misunderstood. The underlying cause is closely related to changes in the male hormone—testosterone. Starting from age 30, men's testosterone levels gradually decline, becoming particularly noticeable after the age of 40.
When testosterone decreases, not only does physical performance decline, but energy levels, mood, and sleep quality can also be negatively affected.
So, how can you tell if you're experiencing this hormonal change? What specific effects might it have, and what can you do about it?
Whether you're a man or a woman, this article has the answers you need.
Jump to Sections:
What Is Testosterone, and Why Does It Matter So Much?
One of my male clients recently told me,
“Something just feels off lately. I’ve lost my drive to exercise, can’t focus at work, and I’m getting irritated over the smallest things. Am I just tired—or is something wrong with me?”
Many men over 40 feel the same way, yet few realize what’s really going on. The truth is, a crucial hormone may be gradually “logging off” in the background — it’s called testosterone.
Testosterone is a type of androgen, a hormone primarily produced in the testicles. While women also have small amounts of it, in men it plays a far more dominant role — not only in sex drive, but in energy, muscle, mood, and metabolism. Think of it as your body's internal “metabolic engine” and “emotional regulator.”
Here are just a few vital roles testosterone plays in your body:
- Muscle building & fat distribution: Supports lean muscle mass, helps maintain metabolic rate, and prevents fat accumulation — especially around the abdomen.
- Bone health: Stimulates bone density and helps reduce the risk of osteoporosis.
- Mood & cognitive function: Low testosterone is linked with irritability, low mood, and trouble concentrating.
- Sexual function: Crucial for libido, erectile quality, and fertility.
- Red blood cell production: Supports oxygen delivery and endurance by boosting red blood cell count.
🔬 Did you know? Testosterone peaks in your 20s, then declines about 1% per year. By age 40, some men may have lost over 15% of their baseline level — but often mistake the symptoms as “just getting older.”
When testosterone drops, your entire system slows down — mentally and physically. You might feel more fatigued, sluggish, and not quite like yourself.
To be clear, more testosterone isn’t always better. But when levels fall below optimal, multiple systems begin to suffer. Testosterone is your body’s master coordinator — even though you can’t see it, it’s constantly managing your energy, strength, emotions, metabolism, and even immune health.
So if you’re over 40 and wondering why you’re not feeling like “you” anymore — the answer might not be laziness or aging.
It might just be that your testosterone is quietly switching off.
And understanding that is the first step toward getting your vitality back.
What Are the Common Symptoms of Low Testosterone?
Testosterone isn’t as “obvious” as blood sugar or cholesterol levels on a health report. It’s more like a system working silently in the background. But once it starts to decline, the body quietly begins to send signals.
Here are the most common symptoms of low testosterone — if several of these resonate with you, it might be time to pay attention to your hormone status:
📱 This table is long — scroll up and down to view all entries:
| Does this sound like you? | What your body is really telling you | Example scenario |
|---|---|---|
| Noticeable drop in energy, easily fatigued | You might find yourself doing nothing after work, losing interest in activities you used to love. | You used to go for a 5km run after work — now you collapse on the couch, too tired to even change clothes. |
| Muscle loss, reduced strength | Even with regular workouts, your muscle tone fades and your lifting strength drops. | Your squat weight dropped from 80kg to 60kg, and recovery feels slow and painful. |
| Increased belly fat, especially a “beer belly” | Your diet hasn't changed, but your waistline grows, and belly fat is harder to lose. | You need to suck in your stomach to zip your old pants, and the belly still bulges out. |
| Lower libido, fewer morning erections | A drop in sexual desire might not be psychological — it could be hormonal. | You used to wake up with morning wood regularly; now it hasn’t happened all week. |
| Poor sleep quality | You may wake up at night, have trouble falling asleep, or feel tired even after sleeping. | You wake up at 3 AM and can’t fall back asleep; the next day, you're drained and foggy. |
| Mood swings, anxiety or irritability | Low testosterone affects neurotransmitters, making you moodier or more reactive. | Someone forgets to reply to your text and you snap — even you’re surprised by your anger. |
| Trouble focusing, slower reaction time | It becomes hard to concentrate — you catch yourself zoning out often. | You start writing an email, but two lines in, you're scrolling your phone or lost in thought. |
| Poor temperature regulation — unusually cold or hot | Testosterone affects autonomic nerves, and lower levels can slow this response. | You used to feel fine in air conditioning — now you need a jacket, or you're sweating easily. |
Note: These symptoms may seem unrelated at first glance, but they share a common root — declining testosterone support.
How Can You Tell If Your Testosterone Levels Are Low?
When people first hear about “low testosterone,” their immediate response is often:
“I’ve had a checkup—my testosterone was within the normal range, so I’m probably fine, right?”
But in reality, many people with low testosterone have lab results that look completely “normal.” Why is that?
First, normal range ≠ optimal range
The “reference range” on your lab report is usually a broad statistical range based on population data—it doesn’t guarantee that everyone within that range is in good health.
For example, one lab might list a total testosterone reference range of 300–1000 ng/dL. A 40-year-old man with a result of 320 ng/dL is technically “within range,” but that number might be significantly lower than his baseline at age 20. His body may already be signaling a lack of energy.
The key isn’t whether you’re still “normal,” but whether you’ve returned to your personal optimal level.
Second, free testosterone is the real player
Most checkups only measure total testosterone, but less than 2% of that is freely circulating and active—this portion is called free testosterone, and it’s the part that actually produces physiological effects.
Many men have normal total testosterone levels, but due to elevated SHBG (sex hormone-binding globulin), the proportion of free testosterone drops—leading to classic low-T symptoms.
To determine whether you’re truly “hormonally offline,” you need to look beyond total levels and assess your active testosterone.
Third, hormone sensitivity varies from person to person
Some individuals are highly sensitive to testosterone fluctuations—even small drops trigger strong symptoms. Others adapt well, showing signs only when levels fall past a certain threshold.
Moreover, factors like stress, sleep, nutrition, and chronic inflammation can all impact how effectively your body uses testosterone.
In other words, it’s not just about hitting a red-flag number—it’s about interpreting lab results in the context of your symptoms, age, and lifestyle.
If you want a clearer picture of your testosterone status, start from these two directions:
- Subjective evaluation: Do you experience fatigue, irritability, low libido, poor focus, or other symptoms mentioned in this article? If 3–4 or more apply, it’s worth paying attention.
- Professional testing: In addition to total testosterone, consider measuring free testosterone, SHBG, and LH (luteinizing hormone) for a more complete hormonal profile.
What Natural Methods Can Help Boost Your Testosterone?
Testosterone secretion peaks mostly during deep sleep stages at night. Lack of deep sleep significantly suppresses the secretion of LH (luteinizing hormone) and GnRH (gonadotropin-releasing hormone), leaving you feeling “tired after sleep” and low on energy during the day. If you struggle to fall asleep, wake up frequently, or have vivid dreams, fixing your sleep rhythm should be your top priority.
Testosterone plays a key role in muscle growth and fat metabolism. In return, strength-focused workouts (like squats, weighted exercises, burpees) stimulate testosterone production. If you sit all day and avoid movement, your body may assume it doesn’t need testosterone either.
Testosterone is a steroid hormone, meaning its raw materials come from cholesterol and fatty acids. If you’ve been eating a very low-fat diet, or rely only on plant oils while avoiding saturated fats, omega-3s, and cholesterol sources, you might not be supplying the building blocks testosterone needs.
These three nutrients are considered “foundational builders.” Research shows they are essential for testosterone synthesis and receptor sensitivity. People who follow long-term vegetarian diets, get little sunlight, or have poor digestion are especially prone to deficiencies, which can hinder testosterone production.
Chronic stress increases cortisol — testosterone’s competitive inhibitor. When cortisol remains high, it not only directly suppresses testosterone production but also disrupts the brain-pituitary-gonadal (HPG) axis, impairing hormonal signaling. The result? Your body has the capacity, but it simply won’t engage.
Authors:
Michelle Ordner
Registered Nurse (RN)
Michelle's expertise spans healthcare, nutrition infusion, and menopausal care. She began her nursing career in New Zealand in 1991 and has since served 17 years in critical care across the USA. After returning to NZ, she trained in cosmetic medicine and stem cell therapy, and holds a UK certification in intravenous nutrition. Her work focuses on integrative care for menopausal health and wellness.
