Persistent fatigue in men usually traces back to one of a handful of causes: poor sleep quality, hormonal shifts, nutritional gaps, unrecognized depression, or metabolic problems like insulin resistance. The tricky part is that these overlap, and more than one can be at play simultaneously. Here’s a breakdown of the most common reasons men feel exhausted, what to look for, and how to start narrowing it down.
Sleep Apnea: The Hidden Energy Thief
Obstructive sleep apnea is one of the most underdiagnosed causes of chronic tiredness in men. Your airway partially or fully collapses during sleep, interrupting breathing dozens or even hundreds of times per night. You may never fully wake up during these episodes, so you have no idea it’s happening. The result is sleep that looks adequate on paper (seven or eight hours) but leaves you feeling wrecked in the morning.
The classic nighttime signs include loud snoring, gasping or choking during sleep (often noticed by a partner), and frequent trips to the bathroom. During the day, the fallout shows up as excessive sleepiness, morning headaches, dry mouth when you wake up, trouble concentrating, irritability, and reduced interest in sex. Men with untreated sleep apnea sometimes also develop hard-to-control high blood pressure. If you snore heavily and feel unrefreshed no matter how long you sleep, a sleep study is the definitive next step.
Low Testosterone
Testosterone levels in adult men normally range from about 300 to 1,000 ng/dL. Production peaks in your late teens and early twenties, then gradually declines, roughly 1% per year after age 30. When levels drop below the lower end of that range, fatigue is often the first and most noticeable symptom. You may also notice reduced motivation, lower sex drive, difficulty building or maintaining muscle, increased body fat, and brain fog.
Low testosterone can result from aging alone, but it’s also driven by obesity, chronic stress, poor sleep, and certain medications. A simple morning blood draw can measure your total testosterone. If results come back borderline, your doctor may repeat the test since levels fluctuate day to day and are highest in the morning.
Thyroid Problems
An underactive thyroid (hypothyroidism) slows your metabolism, and fatigue is its hallmark symptom. Other signs include unexplained weight gain, sensitivity to cold, joint and muscle pain, dry skin, thinning hair, a slower-than-normal heart rate, and low mood. Men tend to dismiss these as normal aging, which is why hypothyroidism often goes undetected for years.
A thyroid panel, which measures thyroid-stimulating hormone (TSH) and free T4, is a straightforward blood test. Because many hypothyroidism symptoms mirror those of low testosterone, depression, and iron deficiency, testing is the only reliable way to tell the difference.
Depression You Might Not Recognize
Depression in men frequently doesn’t look like the stereotype of sadness and crying. Men are more likely to notice and report the physical symptoms of depression, like persistent tiredness and weight changes, rather than describing themselves as feeling low. Irritability, anger, frustration, risk-taking behavior, and withdrawal from social life are all common presentations in men that don’t fit the traditional diagnostic picture.
This means many men experience depression primarily as exhaustion and a short fuse, never connecting it to a mood disorder. If your fatigue comes with a loss of interest in things you used to enjoy, difficulty sleeping (or sleeping too much), concentration problems, or a general sense that everything takes more effort than it should, depression is worth considering seriously.
Iron Deficiency
Iron deficiency isn’t just a women’s health issue. In men, the most common cause is slow, internal blood loss, often from the gastrointestinal tract. Peptic ulcers, colon polyps, colorectal cancer, hiatal hernias, and inflammatory bowel conditions like Crohn’s disease or ulcerative colitis can all cause chronic low-grade bleeding you’d never notice. Regular use of over-the-counter pain relievers like aspirin, ibuprofen, or naproxen can also cause internal bleeding over time.
Celiac disease and previous stomach surgeries (including gastric bypass) reduce your gut’s ability to absorb iron, creating deficiency even if your dietary intake is adequate. Because iron is essential for carrying oxygen to your cells, a shortage directly translates to fatigue, weakness, and poor exercise tolerance. Iron studies, including serum iron, ferritin, and transferrin saturation, are part of a standard fatigue workup. In men, finding iron deficiency usually prompts further investigation into where the blood loss is coming from.
Vitamin D Deficiency
Low vitamin D is extremely common, particularly in men who spend most of their time indoors or live in northern latitudes. Fatigue is a well-documented symptom, alongside muscle weakness and bone pain. The recommended daily intake for men under 70 is 600 IU (15 mcg), but many people fall short of that, especially during winter months. A blood test measuring 25-hydroxyvitamin D is the standard way to check your levels.
Insulin Resistance and Blood Sugar
Insulin is the hormone that moves glucose from your blood into your cells, where it’s converted to energy. When your cells stop responding to insulin efficiently (a condition called insulin resistance), glucose builds up in the bloodstream instead of fueling your muscles and organs. The result is fatigue that doesn’t improve with rest, because the problem isn’t sleep. It’s that your cells are literally starved for energy despite plenty of glucose being available.
Insulin resistance is strongly linked to carrying excess weight, especially around the midsection, and it’s a precursor to type 2 diabetes. Other signs include increased thirst, frequent urination, and difficulty losing weight. A fasting glucose test or a hemoglobin A1C test can reveal whether your blood sugar regulation is off.
Alcohol and Sleep Quality
Even moderate drinking can undermine your energy levels. Alcohol before bed may help you fall asleep faster, but it disrupts your circadian rhythm and suppresses REM sleep, the restorative stage your brain needs most. The result is a rebound effect: you fall asleep quickly, then wake up repeatedly in the second half of the night and feel groggy the next morning. If you drink regularly in the evening and feel perpetually tired, cutting alcohol for two to three weeks is one of the simplest experiments you can run.
Getting Tested
When fatigue lasts more than a few weeks and isn’t explained by obvious sleep deprivation, a targeted set of blood tests can cover most of the medical causes. The CDC’s recommended workup for persistent fatigue includes a complete blood count, fasting glucose, kidney and liver function panels, electrolytes, calcium, a thyroid panel (TSH and free T4), iron studies (serum iron, ferritin, transferrin saturation), C-reactive protein (a marker of inflammation), celiac disease screening, and a urinalysis. Many providers also add vitamin D, B12, and folate levels to the initial panel.
For men specifically, requesting a morning testosterone level is reasonable, especially if fatigue is accompanied by low libido or mood changes. These tests aren’t exotic or expensive, and they can rule out or confirm most of the conditions described above in a single visit. If everything comes back normal, that itself is useful information: it shifts attention toward sleep quality, mental health, lifestyle factors, or less common causes that may need a specialist’s input.