Functional Health · 7 min read

Why You're Always Tired: The 4 Root Causes Most Doctors Miss

If you've been to your doctor complaining of fatigue and been told your labs are "normal," you're not alone. Chronic tiredness is one of the most common complaints I hear from new clients — and it's also one of the most misunderstood. Conventional medicine often looks for disease. Functional medicine looks for dysfunction — and there's a big difference.

1. Subclinical Thyroid Dysfunction

Standard thyroid panels typically only measure TSH. But TSH alone misses a significant portion of thyroid dysfunction. A comprehensive thyroid panel includes free T3, free T4, reverse T3, and thyroid antibodies. Many women with "normal" TSH have conversion issues or autoimmune activity that conventional labs won't catch.

Signs this might be you: fatigue that's worse in the morning, difficulty losing weight, brain fog, hair thinning, and feeling cold when others are comfortable.

2. HPA Axis Dysregulation

Your hypothalamic-pituitary-adrenal (HPA) axis regulates your stress response and cortisol production. Chronic stress can dysregulate this system, leading to abnormal cortisol patterns that leave you wired at night and exhausted in the morning. A 4-point salivary cortisol test maps your cortisol curve throughout the day and reveals patterns that explain your energy crashes.

3. Nutrient Deficiencies

Even with a "healthy" diet, nutrient deficiencies are remarkably common. The most energy-critical nutrients — B12, iron, ferritin, magnesium, Vitamin D, and CoQ10 — are often tested incompletely or with reference ranges that are far too broad.

• Ferritin should be above 70 ng/mL for optimal energy — not just above 12 (the conventional cutoff)
• Vitamin D optimal range is 60–80 ng/mL, not just "not deficient"
• Magnesium — red blood cell magnesium is far more accurate than serum

4. Blood Sugar Dysregulation

Even without diabetes, blood sugar swings are one of the most common causes of energy crashes and afternoon fatigue. A fasting insulin level and a 2-hour post-meal glucose test can reveal insulin resistance years before it shows up as prediabetes on a standard panel.

What to Do Next

If you're exhausted and have been told everything is "normal," the answer isn't to accept it — it's to ask better questions and run better tests. A functional medicine approach looks at your full picture: labs, symptoms, lifestyle, stress, sleep, and nutrition together.