Persistent fatigue in men usually has a identifiable cause, and often more than one. The most common culprits are poor sleep quality, low testosterone, blood sugar problems, nutritional deficiencies, and depression. The good news is that most of these are treatable once you know what you’re dealing with.
If you’ve felt drained for weeks or months despite getting what seems like enough sleep, something specific is likely going on. Here’s what to consider, starting with the causes men most frequently overlook.
Low Testosterone
Testosterone directly influences energy and endurance in men. When levels drop below 300 nanograms per deciliter (ng/dL), the clinical threshold for low testosterone, fatigue is one of the most common complaints. But that 300 ng/dL cutoff may actually be too generous for younger men. Research published in The Journal of Urology found that age-specific cutoffs for low testosterone are considerably higher: around 409 ng/dL for men in their early twenties, dropping to roughly 350 ng/dL by the early forties. A 28-year-old sitting at 320 ng/dL might technically be above the standard cutoff but well below normal for his age.
Beyond fatigue, low testosterone often shows up as reduced motivation, difficulty building or maintaining muscle, increased body fat (especially around the midsection), lower sex drive, and mood changes that can look a lot like depression. These symptoms creep in gradually, which is why many men assume they’re just “getting older” rather than dealing with a hormonal issue. A simple blood test, ideally drawn in the morning when testosterone peaks, can confirm or rule this out.
Sleep Apnea
You can spend eight hours in bed and still wake up exhausted if your airway is collapsing dozens of times per hour while you sleep. Obstructive sleep apnea is significantly more common in men, particularly before age 50, and it’s one of the most underdiagnosed causes of chronic fatigue. Roughly one billion people worldwide between ages 30 and 69 have it.
Snoring gets most of the attention, but sleep apnea causes a constellation of symptoms that disrupt rest: waking up repeatedly throughout the night, morning headaches, night sweats, and gasping or choking sensations. Many men don’t remember these awakenings at all. They just know they feel terrible during the day. The severity is measured by how many times per hour your breathing is disrupted. Five to 15 events per hour is considered mild, 15 to 30 is moderate, and 30 or more is severe. Even mild sleep apnea can leave you chronically tired because it prevents your brain from cycling through the deeper, restorative stages of sleep.
Risk factors include excess weight, a thicker neck circumference, and a naturally narrow airway. If you snore loudly, wake up with a dry mouth, or your partner has noticed you stop breathing at night, a sleep study is worth pursuing.
Blood Sugar and Insulin Resistance
When your cells stop responding properly to insulin, glucose builds up in your bloodstream instead of getting into cells where it’s needed for energy. Your pancreas compensates by pumping out even more insulin, creating a cycle of blood sugar spikes and crashes that leaves you feeling wiped out, especially after meals heavy in refined carbohydrates.
This condition, called insulin resistance, is extremely common in men and often flies under the radar for years before progressing to prediabetes or type 2 diabetes. The fatigue tends to be worst after eating, particularly meals built around white bread, pasta, sugary drinks, or other high-glycemic foods that cause a rapid spike followed by a steep drop. You might also notice increased thirst, frequent urination, brain fog, or stubborn belly fat that won’t budge despite exercise. A fasting glucose test or hemoglobin A1c test can reveal whether your blood sugar regulation is off.
Thyroid Problems
Your thyroid gland controls your metabolic rate, essentially how quickly your body converts food into energy. When it underperforms (hypothyroidism), everything slows down. Fatigue is the hallmark symptom, but it’s usually accompanied by weight gain, sensitivity to cold, joint and muscle pain, dry skin, thinning hair, a slower heart rate, and low mood.
Men tend to think of thyroid problems as a “women’s issue,” which means they’re less likely to bring it up and less likely to get tested. But hypothyroidism absolutely affects men and can develop at any age. A thyroid panel measuring TSH and free T4 is part of a standard fatigue workup and takes minutes to run.
Vitamin B12 and Iron Deficiency
B12 is essential for producing red blood cells and maintaining your nervous system. When you’re deficient, your body can’t efficiently deliver oxygen to tissues, and the result is a deep, persistent tiredness that rest doesn’t fix. Other signs include pale skin, a sore tongue, numbness or tingling in your hands and feet, difficulty concentrating, and memory problems. Men who eat little or no meat, take certain acid-reducing medications, or have digestive conditions that impair absorption are at higher risk.
Iron deficiency works through a similar mechanism: fewer healthy red blood cells means less oxygen reaching your muscles and brain. Low iron is less common in men than women (since men don’t lose blood monthly), but it still happens, particularly with poor diet, chronic inflammation, or undiagnosed gastrointestinal bleeding. Both deficiencies are easily identified through blood work and straightforward to treat.
Depression and Mental Exhaustion
Depression in men often doesn’t look the way people expect. Rather than sadness, the dominant symptom is frequently a crushing physical exhaustion where even small tasks take enormous effort. Thinking feels slower, speaking takes more energy, and motivation evaporates. You might also experience unexplained physical problems like back pain or headaches, sleep disturbances (either insomnia or sleeping far too much), and irritability.
Men are less likely to recognize these symptoms as depression and more likely to attribute them to stress or aging. But depression causes measurable changes in brain chemistry that directly affect energy levels. It also creates a vicious cycle: fatigue leads to inactivity, which worsens mood, which deepens fatigue. If you’ve lost interest in things you used to enjoy, feel emotionally flat, or notice that your energy problems came on alongside a difficult period in your life, depression deserves serious consideration.
How Alcohol Disrupts Your Sleep
Even moderate drinking sabotages sleep quality in ways you probably don’t notice. Alcohol initially makes you fall asleep faster and increases deep sleep during the first half of the night, which is why a nightcap can feel effective. But in the second half of the night, everything falls apart. Research on controlled alcohol consumption found that drinking before bed significantly decreased sleep efficiency in the second half of the night, with more time spent awake after initially falling asleep and a sharp reduction in deep sleep. REM sleep, the stage critical for mental restoration and memory, was suppressed throughout the entire night with no rebound in the second half.
The result is that you get less restorative sleep even if you slept for the same total number of hours. If you’re drinking three or more nights a week, this alone could explain a significant portion of your fatigue.
Getting the Right Blood Work
If fatigue has lasted more than a few weeks and isn’t explained by obvious lifestyle factors, a thorough blood panel can identify or rule out most medical causes. A standard fatigue workup typically includes a complete blood count, fasting glucose, thyroid function (TSH and free T4), iron studies (including ferritin and transferrin saturation), liver and kidney function panels, and markers of inflammation like C-reactive protein. Many providers also include B12, folate, and vitamin D levels in the initial round of testing.
For men specifically, requesting a total testosterone level is important, since it’s not always included in standard panels. If autoimmune disease is suspected based on your symptoms, additional tests like antinuclear antibodies may be added. Celiac disease screening is also part of a comprehensive fatigue evaluation, since gluten sensitivity can cause chronic exhaustion even without obvious digestive symptoms.
Most of these tests can be run from a single blood draw. If everything comes back normal, that information is still valuable: it narrows the focus to sleep quality, mental health, and lifestyle factors that blood work can’t capture.