Feeling Tired Constantly? The 7 Root Causes of Chronic Fatigue Your Doctor Should Test

You're exhausted - not the kind of tired that improves after a good night's sleep, but the bone-deep fatigue that makes even simple tasks feel insurmountable. You've tried sleeping more, drinking extra coffee, and pushing through, but nothing helps. When you finally mention it to your doctor, you're told your basic lab work looks "normal" and perhaps you just need to manage your stress better.

But what if your fatigue isn't normal at all? What if there are identifiable, treatable root causes that standard testing simply isn't designed to catch?

If you're constantly tired despite adequate rest, struggling with low energy that interferes with daily life, or feeling like you're running on empty no matter what you do, it's time to dig deeper. Chronic fatigue is not a character flaw or something you simply have to accept; it's your body's way of signaling that something needs attention.

Why "Normal" Lab Work Doesn't Always Mean You're Fine

Here's a frustrating reality: conventional lab testing often looks at a narrow set of markers and compares them to broad reference ranges that may not reflect your optimal health. A result that falls within the "normal" range for someone else doesn't necessarily mean it's optimal for you, and standard testing may miss subtle but significant imbalances that profoundly impact your energy levels.

Many doctors, working within the constraints of brief appointments and standardized protocols, don't have the time or training to investigate the complex, multifaceted nature of chronic fatigue causes. They may check a basic metabolic panel and perhaps a thyroid-stimulating hormone (TSH) level, see that results fall within reference ranges, and conclude that there's nothing wrong.

But fatigue root causes are often more nuanced, involving intricate interactions between multiple body systems, including your thyroid, mitochondria, nutrients, hormones, immune system, and sleep architecture. Understanding what's really happening requires comprehensive testing and a physician who recognizes that "tired all the time" is not a diagnosis - it's a symptom begging for investigation.

Root Cause #1: Thyroid Dysfunction

Your thyroid is often called the "metabolic gas pedal" of your body, and for good reason. This small butterfly-shaped gland in your neck produces hormones that regulate energy production, metabolism, body temperature, and countless other vital functions. When your thyroid isn't functioning optimally, fatigue is often one of the first and most persistent symptoms.

The challenge with thyroid dysfunction and fatigue is that standard testing frequently misses the problem. Most conventional doctors test only TSH (thyroid-stimulating hormone), which measures the pituitary gland's signal to the thyroid - not the actual thyroid hormones circulating in your body. You can have "normal" TSH levels while still experiencing significant thyroid-related fatigue.

Common thyroid issues that cause exhaustion include:

• Subclinical hypothyroidism, where TSH is slightly elevated but still within the broad "normal" range, yet your thyroid hormone production is already declining
• Low T3 syndrome, where your body produces adequate amounts of T4 (the inactive thyroid hormone) but fails to convert it efficiently to T3 (the active form your cells actually use)
• Hashimoto's thyroiditis, an autoimmune condition where your immune system attacks your thyroid gland, causing fluctuating hormone levels and persistent fatigue
• Reverse T3 dominance, where stress or inflammation causes your body to produce an inactive form of T3 that blocks thyroid hormone receptors

Comprehensive thyroid testing should include:

• TSH (thyroid-stimulating hormone)
• Free T4 and Free T3 (the actual hormones your body uses)
• Reverse T3
• Thyroid antibodies (TPO and thyroglobulin) to check for autoimmune thyroid disease

When thyroid function is optimized, many people experience dramatic improvements in energy levels, mental clarity, and overall vitality.

Root Cause #2: Mitochondrial Dysfunction

If you've ever heard mitochondria referred to as the "powerhouses of your cells," there's a profound truth to this description. These tiny structures inside nearly every cell in your body are responsible for producing ATP (adenosine triphosphate), the energy currency that powers everything from your heartbeat to your ability to think clearly.

When mitochondrial function becomes impaired, your cells can't generate adequate energy, and the result is systemic fatigue that no amount of rest seems to fix. Research has shown a remarkable correlation between the degree of mitochondrial dysfunction and the severity of fatigue - particularly in conditions like chronic fatigue syndrome.

Several factors can impair mitochondrial function:

• Nutrient deficiencies (especially CoQ10, B vitamins, magnesium, and L-carnitine)
• Oxidative stress from inflammation or environmental toxins
• Thyroid hormone deficiency (thyroid hormones are essential for optimal mitochondrial function)
• Chronic infections
• Insulin resistance and blood sugar dysregulation

The connection between thyroid function and mitochondrial health is particularly important. Thyroid hormones help deliver oxygen to tissues and are essential for mitochondria to function properly. This means that thyroid dysfunction often leads to mitochondrial dysfunction, creating a compounding effect on your energy levels.

While direct mitochondrial testing (such as ATP profile testing) exists, it's not always widely available. However, an integrative physician can assess your risk factors, evaluate your symptoms, and implement targeted nutritional support to enhance mitochondrial function - often with remarkable improvements in energy.

Root Cause #3: Nutrient Deficiencies

Your body requires a complex array of vitamins, minerals, and other nutrients to produce energy at the cellular level. When you're deficient in even one key nutrient, the impact on your energy can be profound, yet these deficiencies often go undiagnosed because they're not part of standard testing.

The most common nutrient deficiencies that cause fatigue include:

Iron Deficiency and Anemia

Iron is essential for producing hemoglobin, the protein in red blood cells that carries oxygen throughout your body. Without adequate iron, your cells literally can't get enough oxygen to produce energy efficiently. Iron deficiency is the most common nutrient deficiency worldwide and a leading cause of persistent fatigue.

Symptoms often include not just exhaustion, but also pale skin, shortness of breath, dizziness, and cold hands and feet. Comprehensive iron testing should include serum iron, ferritin (stored iron), total iron-binding capacity (TIBC), and transferrin saturation, not just a basic hemoglobin check.

Vitamin B12 Deficiency

Vitamin B12 plays a crucial role in red blood cell formation, nervous system function, and energy metabolism. Deficiency develops slowly but can cause debilitating fatigue, brain fog, memory problems, and even depression. Studies have shown that up to 42% of people with certain chronic conditions have B12 deficiency, and fatigue is significantly more common in those with low levels.

Groups at higher risk include vegetarians and vegans (B12 is found primarily in animal products), older adults (absorption decreases with age), people with digestive disorders, and those taking certain medications like metformin or proton pump inhibitors.

Vitamin D Deficiency

Vitamin D has traditionally been recognized for its role in bone health, but research increasingly shows its importance for energy production, immune function, and mood regulation. Many people living in northern climates or spending limited time outdoors develop vitamin D deficiency, particularly during winter months. Correcting deficiency often leads to noticeable improvements in energy levels and overall wellbeing.

Folate (Vitamin B9) Deficiency

Folate works closely with B12 in red blood cell formation and cellular metabolism. Deficiency can cause fatigue, weakness, and cognitive difficulties. While folate deficiency is less common than B12 deficiency, it's still worth testing - especially if you don't consume adequate fruits and vegetables.

Magnesium Deficiency

Magnesium serves as a cofactor in over 300 enzymatic reactions, many directly involved in energy metabolism and ATP production. Deficiency can cause muscle weakness, cramping, and persistent fatigue that doesn't respond to rest. However, standard blood tests don't accurately reflect cellular magnesium levels, which is why deficiency often goes undiagnosed.

Comprehensive nutritional testing allows your physician to identify and correct these deficiencies with targeted supplementation and dietary changes, often producing dramatic improvements in energy within weeks to months.

Root Cause #4: Sleep Disorders

This might seem obvious (of course sleep problems cause fatigue) - but the relationship is more complex than you might think. Many people experience chronic fatigue not because they're not sleeping enough hours, but because the quality of their sleep is severely compromised by an undiagnosed sleep disorder.

Obstructive Sleep Apnea (OSA)

Sleep apnea occurs when your upper airway becomes repeatedly blocked during sleep, causing breathing to stop and start throughout the night. These interruptions fragment your sleep architecture, preventing you from achieving the deep, restorative stages of sleep your body needs to repair and regenerate.

The result is profound daytime fatigue, brain fog, difficulty concentrating, and increased risk for numerous health conditions. Many people with sleep apnea don't realize they have it; they simply know they wake up exhausted despite spending adequate time in bed.

Risk factors include being overweight, having a large neck circumference, chronic nasal congestion, and certain anatomical features. Interestingly, research shows that untreated sleep apnea is also associated with increased inflammation and may even increase the risk of developing autoimmune conditions, creating another pathway to chronic fatigue.

Insomnia and Sleep Quality Issues

Chronic insomnia - whether difficulty falling asleep, staying asleep, or waking too early -  prevents your body from completing the full sleep cycles necessary for physical and mental restoration. Even if you spend eight hours in bed, if that time is fragmented or doesn't include adequate deep and REM sleep, you'll wake feeling unrefreshed.

Restless Leg Syndrome and Periodic Limb Movement Disorder

These conditions cause uncomfortable sensations in your legs or involuntary leg movements during sleep, significantly disrupting sleep quality and contributing to daytime exhaustion.

If you consistently wake up feeling tired despite adequate time in bed, or if a partner reports that you snore loudly or stop breathing during sleep, a sleep study can identify treatable disorders that may be the root cause of your fatigue.

Root Cause #5: Chronic Infections

Certain chronic infections can trigger persistent fatigue by activating your immune system and creating ongoing inflammation. While acute infections typically resolve with treatment, some infections can persist at low levels, continually taxing your body's resources and energy production.

Infections commonly associated with chronic fatigue include:

• Epstein-Barr Virus (EBV), which causes mononucleosis and can remain dormant in your body, occasionally reactivating and causing fatigue, sore throat, and swollen lymph nodes
• Cytomegalovirus (CMV), a herpes virus that can cause chronic low-grade symptoms
• Lyme disease and associated co-infections, which can cause profound, debilitating fatigue along with other symptoms
• Candida overgrowth in the gut, which can contribute to systemic inflammation and fatigue
• Other chronic viral, bacterial, or parasitic infections

Testing for chronic infections requires more than standard lab work. Specialized testing can identify active infections, reactivated viruses, or evidence of ongoing immune system activation. When these infections are identified and appropriately treated, energy levels often improve significantly.

Root Cause #6: Hormonal Imbalances

Hormones are powerful chemical messengers that regulate nearly every function in your body, including energy production, metabolism, sleep, mood, and stress response. When your hormones fall out of balance, fatigue is often one of the first symptoms.

Beyond thyroid dysfunction (covered earlier), other hormonal imbalances that can cause exhaustion include:

Adrenal Dysfunction and Cortisol Dysregulation

Your adrenal glands produce cortisol, often called the "stress hormone," which plays a crucial role in energy regulation, immune function, and your body's stress response. Chronic stress can dysregulate cortisol production, leading to either elevated cortisol (which disrupts sleep and causes anxiety) or low cortisol (which causes profound fatigue, especially in the morning).

The hypothalamic-pituitary-adrenal (HPA) axis (the system that regulates stress response) becomes dysregulated in many people with chronic fatigue. This creates a vicious cycle where fatigue increases stress, which further disrupts cortisol production.

Sex Hormone Imbalances

As discussed in our article on testosterone for women, sex hormones play crucial roles in energy production that extend far beyond reproductive function. Low testosterone in both men and women can cause fatigue, decreased motivation, difficulty building muscle, and reduced vitality.

Similarly, estrogen and progesterone imbalances during perimenopause and menopause can significantly impact energy levels, sleep quality, and overall wellbeing.

Insulin Resistance and Blood Sugar Dysregulation

When your cells become resistant to insulin, your body struggles to efficiently use glucose for energy. This leads to blood sugar swings, energy crashes, increased inflammation, and persistent fatigue. Testing hemoglobin A1C and fasting insulin (not just fasting glucose) can identify insulin resistance even in its early stages.

Comprehensive hormone testing and optimization, when guided by a physician experienced in integrative medicine, can address these imbalances and restore energy from a foundational level.

Root Cause #7: Inflammation and Autoimmunity

Chronic inflammation is increasingly recognized as a root cause of numerous health conditions, including persistent fatigue. When your immune system remains activated over time - whether due to autoimmune disease, chronic infection, environmental toxins, or other triggers - it creates system-wide inflammation that drains your energy reserves.

Autoimmune Conditions and Fatigue

Profound and debilitating fatigue is one of the most common complaints among people with autoimmune diseases such as:

• Rheumatoid arthritis
• Lupus (systemic lupus erythematosus)
• Multiple sclerosis
• Celiac disease
• Hashimoto's thyroiditis
• Sjögren's syndrome
• Inflammatory bowel disease

In autoimmune conditions, your immune system mistakenly attacks your own tissues, creating ongoing inflammation that affects energy production at the cellular level. The inflammatory molecules (cytokines) released during this process directly interfere with sleep regulation, mitochondrial function, and overall vitality.

Many people live with undiagnosed autoimmune conditions for years before receiving proper diagnosis. If you experience persistent fatigue along with other symptoms like joint pain, digestive issues, skin changes, or recurring infections, screening for autoimmune markers may reveal the underlying cause.

Chronic Inflammation Testing

Even without diagnosed autoimmune disease, chronic low-grade inflammation can significantly impact your energy. Testing for these inflammatory markers is vital:

• High-sensitivity C-reactive protein (hs-CRP)
• Erythrocyte sedimentation rate (ESR)
• Specific autoimmune antibodies (ANA, RF, anti-CCP, thyroid antibodies, celiac panel)

These tests can identify inflammation and immune system activation that may be driving your fatigue. Addressing the root causes of inflammation - whether through diet, lifestyle modifications, stress management, or targeted treatment - often leads to significant improvements in energy and overall health.

The Be Well Approach: Comprehensive Testing and Root Cause Medicine

Dr. Leah Cordovez, founder and Lead Physican at Be Well, understands that chronic fatigue deserves compassion and comprehensive investigation, not dismissal. As a triple board-certified physician in Internal Medicine, Integrative Medicine, and Obesity Medicine, Dr. Cordovez recognizes that persistent exhaustion is not simply "just stress" or "happens to everybody.”

The integrative approach to chronic fatigue involves:

Comprehensive Testing

Rather than relying on basic lab panels that often miss the nuances of hormonal, nutritional, and metabolic dysfunction, comprehensive testing evaluates:

• Complete thyroid panel (TSH, Free T4, Free T3, Reverse T3, thyroid antibodies)
• Nutritional status (iron studies, B12, methylmalonic acid, folate, vitamin D, magnesium, and other essential nutrients)
• Hormone levels (cortisol, DHEA, sex hormones, insulin, hemoglobin A1C)
• Inflammatory markers and autoimmune screening
• Sleep quality assessment & optimization
• Evaluation for chronic infections when indicated

Individual Context Matters

Your symptoms, medical history, lifestyle factors, and health goals all inform the testing strategy and treatment approach. What matters isn't just whether your lab values fall within a reference range; it's whether your body is functioning optimally for you.

Treating Root Causes, Not Just Symptoms

Once testing identifies the underlying causes of your fatigue, treatment focuses on addressing these root issues through:

• Targeted nutritional supplementation to correct deficiencies
• Hormone optimization when appropriate
• Thyroid treatment that goes beyond standard T4 replacement
• Support for mitochondrial function and energy production
• Anti-inflammatory interventions through diet, lifestyle, and targeted therapies
• Sleep optimization strategies
• Treatment of underlying infections or autoimmune conditions

A Partnership Approach

Healing from chronic fatigue takes time and requires a dynamic partnership between you and your physician. The whole-person approach at Be Well means creating a treatment plan that evolves with you, adjusting strategies as your body responds and your needs change.

You Don't Have to Accept Feeling Exhausted

If you've been told your fatigue is "just stress," "just depression," or "just part of getting older," you deserve better answers. Chronic fatigue has identifiable root causes, and comprehensive testing can uncover what's really happening in your body.

You don't have to continue pushing through exhaustion, relying on caffeine to function, or watching life pass by from the sidelines because you simply don't have the energy to participate. With proper testing, identification of root causes, and comprehensive treatment, most people experience significant - sometimes dramatic - improvements in their energy levels and quality of life.

The first step is finding a physician (like Dr. Cordovez) who will listen to your concerns, take your symptoms seriously, and commit to investigating thoroughly until answers are found. At our friendly Tennessee practice, that kind of comprehensive, compassionate care is what you can always expect.

Being tired all the time isn't a life sentence - you deserve to wake up feeling refreshed, to have energy for the activities you love, and to feel like yourself again. That journey begins with asking the right questions, running the right tests, and partnering with a physician who recognizes that your chronic fatigue is not normal, and that you deserve answers and empathetic care.