Low Energy in Men Over 40 — What's Actually Going On

"I'm Just Getting Older" — Maybe. But Probably Not Just That.

Men in their 40s tell me this constantly: "I just don't have the energy I used to." They assume it is aging. Sometimes it is. But more often, there is a specific, treatable cause hiding behind the general fatigue — and nobody has looked for it.

Here is what I actually check when a man over 40 tells me he is exhausted.

The Usual Suspects

Low Testosterone

This is the one everyone thinks of, and for good reason. Testosterone declines about 1-2% per year after age 30. By your mid-40s, you may be 15-30% below your peak. Some men barely notice. Others feel it profoundly — crushing fatigue, brain fog, loss of motivation, decreased strength.

What to test: Total testosterone, free testosterone, SHBG, LH, FSH. Timing matters — blood draw should be fasting, before 10 AM.

What qualifies as low: Total testosterone below 300 ng/dL is the clinical threshold, but many men feel symptomatic at 300-400. Free testosterone may be more informative than total.

Treatment: Testosterone replacement therapy, clomiphene, lifestyle optimization. See our guide on [getting testosterone prescribed online](/blog/can-you-get-testosterone-prescribed-online).

Thyroid Dysfunction

Hypothyroidism is not just a women's condition. About 5% of men over 40 have subclinical hypothyroidism — enough to cause fatigue, weight gain, cold intolerance, and cognitive sluggishness, but often missed because doctors check TSH and stop there.

What to test: TSH, free T4, free T3, thyroid antibodies (TPO, thyroglobulin). TSH alone is not enough.

The gray zone: TSH of 2.5-4.5 is "normal" on most lab ranges but may be symptomatic in some men, especially with positive antibodies.

Sleep Apnea

This is the most underdiagnosed cause of fatigue in men over 40. If you snore, have a neck circumference over 17 inches, or wake up feeling unrefreshed despite sleeping 7-8 hours, obstructive sleep apnea is likely.

Prevalence: Up to 25% of men in their 40s have at least mild sleep apnea. Most are undiagnosed.

The connection: Sleep apnea fragments your sleep architecture, preventing restorative deep sleep. It also lowers testosterone — creating a double hit on energy.

Diagnosis: Home sleep study (much easier than going to a sleep lab). We can order this.

Insulin Resistance / Pre-Diabetes

You do not need to be diabetic to be metabolically dysfunctional. Insulin resistance — where your cells respond poorly to insulin, forcing your pancreas to overproduce it — causes post-meal energy crashes, afternoon fatigue, and that "food coma" feeling that never fully lifts.

What to test: Fasting insulin (not just fasting glucose), hemoglobin A1c, fasting glucose. A fasting insulin above 10-12 suggests resistance even with normal glucose.

The overlooked stat: About 40% of American men in their 40s have insulin resistance. Most do not know it.

Iron and Ferritin

Men rarely think about iron, and doctors rarely check it in men because frank anemia is uncommon. But ferritin (iron storage) can be suboptimal without showing up as anemia on a CBC. Ferritin below 50 can cause fatigue in some men, even though lab ranges go as low as 20-30.

Conversely, hemochromatosis (iron overload) is more common in men and also causes fatigue. A ferritin level tells you which direction you are headed.

Vitamin D

Vitamin D deficiency is epidemic in indoor-working adults, even in Florida. Below 30 ng/mL is deficient. Below 20 is severely deficient. Both correlate with fatigue, muscle weakness, and mood changes.

What to test: 25-hydroxyvitamin D.

Depression and Chronic Stress

This needs to be on the list because it is frequently the actual diagnosis, and men frequently resist it. Depression in men over 40 often presents as fatigue, irritability, and loss of interest — not "sadness" in the classic sense. Chronic cortisol elevation from sustained stress also depletes energy through adrenal and metabolic pathways.

This is not a weakness. It is a medical condition. And it responds to treatment.

The Diagnostic Approach I Use

When a man over 40 comes to me with fatigue, here is my standard workup:

1. Comprehensive metabolic panel — liver, kidneys, electrolytes
2. CBC — anemia, infection markers
3. Thyroid panel — TSH, free T4, free T3
4. Testosterone — total, free, SHBG
5. Fasting insulin and A1c — metabolic health
6. Vitamin D, B12, ferritin — common deficiency causes
7. Sleep assessment — screening for apnea
8. Mental health screen — PHQ-9, GAD-7

This costs $100-$300 at a cash-pay lab. It takes 30 minutes of your time and can identify the specific cause in most cases.

What to Do After Getting Results

Results fall into three categories:

Clear abnormality: Low testosterone, hypothyroidism, severe vitamin D deficiency, sleep apnea. Treat the identified cause. Most men notice improvement within 4-8 weeks.

Borderline values: Testosterone at 350, TSH at 3.5, vitamin D at 28. These are technically "normal" but potentially symptomatic. A knowledgeable physician evaluates these in the context of your symptoms, not just against lab ranges.

Everything normal: If labs are truly normal and sleep is adequate, the conversation shifts to lifestyle factors (exercise, nutrition, stress), mental health evaluation, or less common causes. "Everything is normal" does not mean "nothing is wrong" — it means we need to look in different places.

Get Checked

If you are a man over 40 running on empty, the answer is not more coffee. It is a proper workup. [Start here](/start) — we will order the right labs and figure out what is actually going on.

Related: [TRT cost without insurance](/blog/how-much-does-trt-cost-without-insurance) | [Always tired but bloodwork is normal](/blog/always-tired-but-blood-work-is-normal)