Constant fatigue in men is rarely about not trying hard enough to sleep. It usually points to one or more underlying issues, whether hormonal, nutritional, sleep-related, or psychological. The tricky part is that many of these causes overlap and feed into each other, so pinpointing the right one often requires working through a short list of the most common culprits.
Low Testosterone
Testosterone does more than drive muscle growth and sex drive. It plays a direct role in energy regulation, mood, and mental sharpness. When levels drop, the result is often a persistent, heavy fatigue that sleep doesn’t fix, along with irritability, brain fog, and low motivation. An estimated 4 to 5 million men in the United States have clinically low testosterone, and the condition becomes increasingly common with age. More than 60% of men over 65 have free testosterone levels below the normal range for men in their early 30s.
But this isn’t just an older man’s problem. Research published in The Journal of Urology established age-specific thresholds for men 20 to 44. For men in their 20s, levels below roughly 410 ng/dL may already be low. For men in their late 30s and early 40s, that cutoff sits closer to 350 ng/dL. If your fatigue comes with decreased interest in sex, difficulty concentrating, or a general sense of emotional flatness, testosterone is worth checking with a simple blood draw.
Sleep Apnea
You can spend eight or nine hours in bed and still wake up exhausted if your airway collapses repeatedly throughout the night. Obstructive sleep apnea is significantly more common in men than women, and it’s one of the most underdiagnosed causes of chronic tiredness. The muscles in the back of your throat relax during sleep, partially or fully blocking airflow. Your brain briefly wakes you to reopen the airway, sometimes dozens of times per hour, but you rarely remember it happening.
The classic signs include loud snoring, gasping or choking during sleep, waking up with a dry mouth or morning headache, and needing to urinate frequently at night. During the day, the hallmark is excessive sleepiness that feels disproportionate to how much time you actually slept. A bed partner noticing pauses in your breathing is one of the strongest indicators. You don’t need to be overweight to have sleep apnea, though carrying extra weight around the neck significantly raises the risk. A sleep study, which can now often be done at home, is the standard way to confirm or rule it out.
Depression Looks Different in Men
Depression in men frequently shows up as physical exhaustion rather than sadness. Many men with depression never feel the stereotypical hopelessness or tearfulness. Instead, the dominant symptoms are bone-deep tiredness, irritability that feels out of proportion, headaches, digestive problems, and chronic pain that doesn’t have a clear physical explanation. Sleep disruption is common on both ends: some men can’t fall asleep, while others sleep 10 or 12 hours and still feel drained.
This mismatch between what men experience and what they expect depression to look like means many go years without recognizing what’s happening. If your fatigue arrived alongside a shorter temper, loss of interest in things you used to enjoy, or a creeping sense of emptiness, depression is a real possibility, even if you wouldn’t describe yourself as “sad.”
Iron Deficiency
Iron deficiency isn’t just a concern for women. In men, it’s less common but more medically significant when it does occur, because the most frequent cause is slow, hidden bleeding somewhere in the gastrointestinal tract. Ulcers, celiac disease, and in some cases early-stage cancers of the colon or stomach can all cause gradual iron loss that eventually leads to anemia. One study found that 11% of men with unexplained iron deficiency anemia were diagnosed with a new gastrointestinal cancer. Among men over 65, that figure rose to 9% within two years of the anemia diagnosis.
The fatigue from iron deficiency feels specific: you’re winded climbing stairs, your endurance during exercise drops noticeably, and you may feel lightheaded when standing. Pale skin, cold hands, and brittle nails are other clues. If bloodwork reveals low iron, your doctor will typically recommend investigating the source rather than simply prescribing supplements, because in men the “why” matters as much as the deficiency itself.
Vitamin D Deficiency
Vitamin D levels below 30 ng/mL are considered insufficient, and levels below 10 ng/mL are classified as severely deficient. Men who work indoors, live in northern latitudes, or have darker skin are at particular risk. The fatigue from low vitamin D tends to be generalized and vague, often accompanied by muscle weakness, joint aches, and a mood that dips during winter months. A blood test measuring your 25(OH)D level is the standard way to check, and it’s a reasonable thing to request if you’re investigating unexplained tiredness.
Insulin Resistance and Blood Sugar
If you feel particularly wiped out after meals, your body may be struggling to process glucose efficiently. Insulin resistance occurs when your cells stop responding well to insulin, forcing the pancreas to produce more and more of it to move sugar out of your bloodstream and into cells for energy. The result is a cycle where blood sugar spikes, your body overcompensates, and your energy crashes. Over time, this develops into prediabetes and eventually type 2 diabetes.
Men who carry excess weight around the midsection are at higher risk. Other signs include increased thirst, frequent urination, and patches of darkened skin on the neck or armpits. A fasting glucose or hemoglobin A1C test can reveal whether blood sugar regulation is contributing to your fatigue.
Thyroid Problems
An underactive thyroid (hypothyroidism) slows your metabolism and produces a distinctive kind of fatigue: sluggish, cold, heavy. You may notice weight gain that’s hard to explain, constipation, dry skin, and a feeling like your body is running at half speed. While thyroid disorders are more commonly discussed in women, men develop them too, and the symptoms are easy to dismiss as “just getting older.” A thyroid function test is a standard part of any fatigue workup.
Alcohol and Sleep Quality
Even moderate drinking disrupts sleep architecture in ways you don’t feel in the moment. Alcohol helps you fall asleep faster but significantly reduces the amount of REM sleep you get, which is the restorative phase your brain needs to consolidate memory and regulate mood. During alcohol withdrawal, even just the nightly mini-withdrawal that happens as your body processes a few drinks, REM sleep drops sharply. The result is waking up after a full night feeling unrested, groggy, and mentally dull. If you’re drinking three or more nights a week and wondering why you’re always tired, a two-week break can be surprisingly revealing.
What to Ask Your Doctor
There’s no single blood test for chronic fatigue, but a focused panel can rule out or confirm the most common causes. A reasonable starting point includes a complete blood count (to check for anemia), a metabolic panel (for blood sugar and kidney function), thyroid hormones, testosterone, vitamin D, and iron studies. If results come back normal, sleep apnea screening and a mental health evaluation are the logical next steps.
Before your appointment, it helps to track a few things for a week or two: how many hours you’re sleeping, how many times you wake at night, how much caffeine and alcohol you’re consuming, and whether the fatigue is worse at certain times of day (after meals, in the afternoon, first thing in the morning). These patterns can point your doctor toward the right diagnosis much faster than bloodwork alone.