What causes fatigue?

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Last updated: May 6, 2025View editorial policy

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From the Guidelines

Fatigue is primarily caused by a combination of physical, mental, and lifestyle factors, including medical conditions, mental health issues, and lifestyle choices, as identified in the most recent and highest quality study 1. When evaluating fatigue, it is essential to consider various factors, including onset, pattern, duration, and associated or alleviating factors, as well as disease status and treatable contributing factors such as comorbidities, medications, and lifestyle issues 1. Key factors that contribute to fatigue include:

  • Medical conditions like anemia, thyroid disorders, diabetes, heart disease, and infections
  • Mental health issues such as depression, anxiety, and stress
  • Lifestyle factors like inadequate sleep, poor nutrition, dehydration, lack of physical activity, and excessive alcohol or caffeine consumption
  • Certain medications, including antihistamines, blood pressure medications, and some antidepressants, that may cause drowsiness as a side effect
  • Overexertion without proper recovery time, which depletes energy reserves in the body According to the study 1, management of fatigue begins with primary oncology team members who perform the initial screening and either provide basic education and counseling or expand the initial screening to a more focused evaluation for moderate or higher levels of fatigue. The study 1 also highlights the importance of assessing treatable contributing factors, including pain, emotional distress, sleep disturbance, anemia, nutrition, activity level, alcohol/substance abuse, medication side effects profile, and other comorbidities. It is crucial to consult a healthcare provider if fatigue persists for more than two weeks despite lifestyle improvements to rule out underlying medical conditions 1.

From the Research

Causes of Fatigue

  • Fatigue can be due to a broad spectrum of diseases, including decompensation of already known conditions 2
  • Sleep disorders and sleep-related disorders of breathing, depression (18.5%), and excessive psychosocial stress are the most common causes of persistent fatigue 2
  • Previously undiagnosed cancer is a rare cause, accounting for only 0.6% of cases 2
  • Anemia and other organic causes are rare as well, with anemia accounting for 4.3% of cases 2
  • Iron deficiency anemia can also contribute to fatigue, particularly in patients with primary hypothyroidism 3, 4, 5, 6
  • In patients with coexisting iron-deficiency anemia and subclinical hypothyroidism, treatment of subclinical hypothyroidism can improve response to oral iron therapy and reduce fatigue 6

Relationship Between Fatigue and Other Conditions

  • Fatigue can be a symptom of various conditions, including hypothyroidism, anemia, and sleep disorders 2, 3, 4, 5, 6
  • Iron deficiency anemia can exacerbate hypothyroidism and contribute to fatigue 3, 4, 5, 6
  • Treatment of underlying conditions, such as hypothyroidism and anemia, can help alleviate fatigue 2, 6

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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