What causes men to be tired all the time?

Last Updated: November 11, 2025 | Reading Time: 11 minutes

Understanding Chronic Fatigue in Men

Persistent exhaustion affects millions of men who struggle to understand why they feel drained despite adequate sleep. Unlike ordinary tiredness that improves with rest, chronic fatigue significantly impairs daily functioning and can signal underlying health conditions requiring medical attention.

The distinction between normal tiredness and pathological fatigue matters. A 2024 study published in Nature Communications examined 17 people with chronic fatigue syndrome compared to 21 healthy volunteers. Researchers found decreased brain activity in regions controlling movement and effort, along with immune system dysfunction. Dr. Avindra Nath, the study's senior author, explained that fatigue may arise from a mismatch between what someone thinks they can achieve and what their bodies actually perform.

Chronic fatigue syndrome affects more than 4 million people across the country, with symptoms including profound exhaustion, brain fog, and post-exertional malaise where symptoms worsen after even mild activity. However, chronic fatigue syndrome represents just one potential cause of persistent tiredness in men.

Sleep Disorders and Sleep Apnea

The Hidden Epidemic of Sleep Apnea

Obstructive sleep apnea ranks among the most common yet underdiagnosed causes of male fatigue. This condition occurs when upper airways repeatedly collapse during sleep, causing breathing interruptions that fragment sleep quality and reduce oxygen availability to tissues.

The prevalence of sleep apnea in men is staggering. A large Swiss population study of subjects aged 40 to 85 found that 49% of men have moderate to severe sleep apnea with an apnea-hypopnea index of 15 or higher. The condition is significantly more common in men than women, with several biological factors increasing male susceptibility.

Why men are more vulnerable to sleep apnea:

• Longer airway length increases collapse risk
• Greater volume of soft tissues on lateral pharyngeal walls
• Testosterone may enhance ventilatory instability during sleep
• Higher rates of obesity, a major risk factor for airway obstruction

How Sleep Apnea Causes Fatigue

A 2022 study examining 5,464 patients referred for sleep apnea evaluation found that nearly 70% were men with a median age of 50 years. Among these patients, 42.7% reported excessive sleepiness, while 38.6% experienced pathological fatigue as measured by validated assessment scales.

Sleep apnea causes daytime exhaustion through multiple mechanisms. The repeated breathing interruptions trigger micro-awakenings throughout the night, preventing deep restorative sleep stages. Oxygen desaturations stress the cardiovascular system and contribute to elevated heart rates. A study tracking patients after sleep apnea treatment found that fatigue, tiredness, and lack of energy all improved significantly with positive airway pressure therapy.

Men with sleep apnea frequently complain of symptoms beyond sleepiness. An Egyptian study of 30 patients with obstructive sleep apnea found that 80% reported fatigue as a primary symptom, while 86.7% experienced excessive daytime sleepiness. The research demonstrated that sleep apnea severity correlated with impaired cognitive function and structural brain changes visible on MRI scans.

Low Testosterone and Energy Levels

The Testosterone-Fatigue Connection

Low testosterone represents one of the most frequently overlooked causes of persistent exhaustion in men over 40. The Hypogonadism in Males study found that approximately 38.7% of men aged 45 and older have low testosterone levels, with fatigue being the primary complaint among those affected.

Testosterone plays crucial roles beyond muscle development and sexual function. The hormone influences red blood cell production, which directly impacts oxygen-carrying capacity throughout the body. When testosterone levels drop, reduced red blood cell formation can lead to decreased oxygen availability, contributing to feelings of exhaustion and reduced physical endurance.

Mayo Clinic urologist Dr. Gregory Broderick explains that while sexual dysfunction is the main complaint he sees, fatigue, changes in mental sharpness, less stamina, and mild depression are closely associated with falling testosterone. These symptoms can profoundly impact quality of life, affecting both work performance and personal relationships.

Research on Testosterone Replacement

Studies demonstrate that testosterone replacement therapy can effectively address fatigue in men with confirmed low testosterone. A 2022 study comparing men on testosterone replacement therapy to those receiving placebo found that the treatment group had half the fatigue scores of the control group, indicating significant improvement in energy levels.

Research from 2019 examining men's experiences with testosterone therapy found that improved energy was a top reason for seeking treatment. Over 52% of men using testosterone reported improvements in energy after beginning therapy. Another study of men with late-onset hypogonadism showed that testosterone replacement for more than one year was associated with significantly lower fatigue scores compared to newly diagnosed patients.

Additional symptoms suggesting low testosterone:

• Reduced sex drive and erectile dysfunction
• Loss of muscle mass despite exercise
• Increased body fat, especially around the midsection
• Depression or mood changes
• Difficulty concentrating or memory problems
• Sleep disturbances

One study found that 30% of men who were overweight had low testosterone, compared to only 6% of those with weight in the normal range. In men with Type 2 diabetes, 25% had low testosterone compared to 13% of those without diabetes, highlighting the interconnected nature of metabolic health and hormone balance.

Nutritional Deficiencies

Vitamin D Deficiency

Vitamin D deficiency affects approximately 35% of adults and plays an overlooked role in persistent fatigue. A 2014 study of 174 participants with fatigue found that taking supplementary vitamin D for 5 weeks significantly improved fatigue symptoms, demonstrating a direct connection between vitamin D status and energy levels.

The relationship between vitamin D and fatigue extends beyond simple supplementation. Vitamin D influences inflammatory pathways, immune function, and potentially affects anemia risk. A cross-sectional study found that anemia was present in 49% of vitamin D-deficient subjects compared with 36% with normal vitamin D levels. The odds ratio for anemia in subjects with vitamin D deficiency was 1.9 after controlling for age, gender, and chronic kidney disease.

Research suggests vitamin D may affect fatigue through multiple mechanisms. The vitamin modulates inflammatory cytokines and regulates hepcidin, the hormone responsible for controlling systemic iron concentrations. By supporting red blood cell production and reducing inflammation, adequate vitamin D levels help maintain energy and reduce exhaustion.

Iron Deficiency and Anemia

Iron deficiency represents a common cause of fatigue that often goes unrecognized in men. Iron is essential for producing hemoglobin, the protein in red blood cells that transports oxygen throughout the body. Without adequate iron, tissues receive insufficient oxygen, leading to tiredness, weakness, and decreased physical capacity.

While iron deficiency anemia is more common in women due to menstrual blood loss, men can develop it from various causes including gastrointestinal bleeding, dietary insufficiency, or chronic inflammatory conditions. A study found that 23% of iron-deficient female athletes were three times more likely to have vitamin D deficiency, while vitamin D-deficient women were 2.7 times more likely to have iron deficiency, illustrating the interconnected nature of nutritional status.

B Vitamin Complex

B vitamins serve as essential cofactors in energy metabolism, converting food into usable cellular energy. A 2023 randomized double-blind study evaluated vitamin B supplementation in 32 healthy adults aged 20 to 30. After 28 days of supplementation with vitamins B1, B2, B6, and B12, researchers found significant improvements in physical performance and reductions in physical fatigue.

Vitamin B12 deficiency is particularly problematic for energy levels. More than 3% of adults over age 50 have seriously low levels of vitamin B12, while up to 20% may have borderline deficiency. As people age, stomach acid production decreases, reducing the body's ability to absorb B12 from food. This deficiency manifests as fatigue, weakness, and cognitive difficulties.

Thyroid Dysfunction

Hypothyroidism and Persistent Exhaustion

Hypothyroidism occurs when the thyroid gland fails to produce adequate thyroid hormones, which regulate metabolism throughout the body. The condition affects approximately 5% of people aged 12 years or older, with men comprising 3 to 16% of those diagnosed. Fatigue ranks among the most prominent symptoms, often appearing long before diagnosis.

A prospective study examined 92 patients with primary hypothyroidism, evaluating fatigue levels before and after levothyroxine treatment. After 6 months of thyroid hormone replacement, researchers found significant reductions in thyroid-stimulating hormone levels and substantial improvements across all fatigue assessment measures. However, approximately one-quarter of patients persisted with fatigue despite normalization of thyroid function, suggesting other contributing factors often coexist.

The thyroid's role in energy production helps explain why hypothyroidism causes such profound exhaustion. Thyroid hormones influence nearly every cell in the body, affecting how quickly the body uses energy, makes proteins, and responds to other hormones. When thyroid function drops, metabolism slows, leading to decreased energy production at the cellular level.

Common symptoms of hypothyroidism:

• Persistent fatigue that doesn't improve with rest
• Unexplained weight gain despite normal eating habits
• Increased sensitivity to cold
• Dry skin and hair loss
• Muscle weakness and joint pain
• Depression and cognitive difficulties
• Constipation

Diagnosis and Treatment

Approximately 20 million Americans have thyroid disease, although up to 60% may not know they have it. Women develop thyroid conditions more frequently than men, but male hypothyroidism often goes undiagnosed because fatigue gets attributed to stress, aging, or lifestyle factors rather than hormone imbalance.

Simple blood tests measuring thyroid-stimulating hormone and thyroxine levels can diagnose hypothyroidism. Treatment typically involves daily levothyroxine tablets to replace missing thyroid hormone. A UK survey of people with treated hypothyroidism found that fatigue remains very common and is associated with substantial functional impairments, emphasizing the importance of proper diagnosis and treatment optimization.

Chronic Stress and Mental Health

The Physical Toll of Psychological Stress

Chronic stress exerts profound effects on physical energy through multiple biological pathways. When stress becomes persistent, the body remains in a heightened state of alert, continuously releasing cortisol and other stress hormones. This ongoing activation exhausts the adrenal system and disrupts normal energy metabolism.

Research into chronic fatigue syndrome has identified that stress-related immune dysfunction may trigger lasting fatigue. A 2024 NIH study found that people with chronic fatigue syndrome showed elevated heart rates throughout the day and smaller nighttime drops in heart rate, suggesting dysregulation of the autonomic nervous system that controls unconscious bodily functions.

The mental load of work demands, family responsibilities, and financial pressures creates what researchers call "invisible cognitive work" that drains energy reserves. Men often face societal expectations to maintain stoic composure while managing significant stress, potentially delaying recognition of how psychological burden affects physical vitality.

Depression and Fatigue

Depression and fatigue exist in a bidirectional relationship where each condition can trigger or worsen the other. Fatigue represents one of the nine diagnostic criteria for major depressive disorder, while persistent exhaustion increases vulnerability to developing depression.

Studies examining patients referred for sleep disorders found that 19% had symptoms of depression and 28.4% showed symptoms of anxiety. These mental health conditions frequently coexist with physical causes of fatigue, creating complex presentations that require comprehensive evaluation rather than single-cause thinking.

Brain imaging studies of people with chronic fatigue syndrome revealed decreased activity in the temporal-parietal junction, a brain region involved in perceiving fatigue and generating effort. This finding suggests that some types of persistent exhaustion involve altered brain signaling rather than simply physical depletion, explaining why rest alone may not resolve the problem.

Lifestyle and Physical Inactivity

The Paradox of Exercise and Energy

Physical inactivity contributes significantly to persistent fatigue, creating a self-perpetuating cycle where exhaustion leads to less movement, which further reduces energy levels. A cohort study examining childhood predictors of adult chronic fatigue syndrome found that 10-year-old children who were reported to "never or hardly ever" play sport in their spare time had twice the risk of developing chronic fatigue syndrome as adults.

Research consistently shows that sedentary patients with chronic fatigue syndrome are at least as physically deconditioned as sedentary but healthy people. Lack of fitness and inactivity predicted the development of chronic fatigue syndrome after infectious mononucleosis, suggesting that either premorbid fitness levels or early deconditioning serves as a risk factor.

The mechanism linking inactivity to fatigue extends beyond simple deconditioning. Physical activity influences multiple body systems including cardiovascular fitness, metabolic efficiency, sleep quality, and mood regulation. Regular movement also helps regulate stress hormone production and supports healthy testosterone levels in men.

Sleep Hygiene and Circadian Rhythms

Poor sleep habits compound other causes of fatigue. Research shows that restricting sleep to five hours per night decreases daytime testosterone levels by 10 to 15% among healthy young men, demonstrating how inadequate sleep disrupts hormone production beyond just causing tiredness.

Circadian rhythm disruptions from shift work, irregular schedules, or excessive evening screen time interfere with the body's natural sleep-wake cycle. This misalignment between internal biological clocks and external demands creates a state of chronic jet lag that impairs energy, cognition, and overall health.

Comparison: Common Causes of Male Fatigue

When Multiple Causes Overlap

Most men with persistent fatigue have more than one contributing factor. A man with sleep apnea may also have low testosterone, as poor sleep quality disrupts hormone production. Someone with vitamin D deficiency might develop iron deficiency anemia, since vitamin D influences iron absorption and utilization.

This interconnected nature of fatigue causes explains why comprehensive medical evaluation proves essential. Treating only one factor when several contribute may provide partial improvement but leave residual exhaustion. A systematic approach examining sleep quality, hormone levels, nutritional status, thyroid function, and mental health typically yields the most complete understanding and effective treatment strategy.

Frequently Asked Questions

Key Takeaways

The Path Forward

Persistent fatigue deserves thorough medical investigation rather than acceptance as an inevitable part of aging or busy lifestyles. The high prevalence of treatable conditions like sleep apnea, low testosterone, and nutritional deficiencies means most men with chronic exhaustion can achieve significant improvement through proper diagnosis and treatment.

The interconnected nature of factors contributing to fatigue emphasizes the value of comprehensive evaluation. A systematic approach examining multiple potential causes simultaneously typically yields better outcomes than addressing single factors in isolation. Working with healthcare providers who take fatigue seriously and investigate thoroughly offers the best path to reclaiming energy and vitality.

If you're experiencing persistent tiredness despite adequate sleep, consider scheduling a medical evaluation. Simple blood tests can identify many common causes, while sleep studies can diagnose conditions like sleep apnea that fragment rest quality. Taking action to understand and address the root causes of exhaustion represents an investment in long-term health, productivity, and quality of life.

For more information on natural energy solutions, read our guide on the best supplements for sustained stamina in men.