Common Causes of Fatigue
1. Iron Deficiency & Anaemia
One of the most important causes, particularly in women. Iron is essential for haemoglobin and oxygen transport. When haemoglobin falls, tissues receive less oxygen, causing persistent tiredness, reduced exercise capacity, breathlessness on climbing stairs, palpitations, headache, dizziness and poor concentration. Low iron stores may contribute to fatigue even before obvious anaemia develops — serum ferritin can be useful.
2. Vitamin B12 Deficiency
B12 deficiency can produce fatigue, poor concentration, memory difficulty, pins-and-needles sensations, numbness, burning feet and balance problems in addition to macrocytic anaemia. People consuming little or no animal-derived food, those with poor absorption (pernicious anaemia, previous gastric surgery, intestinal disease) or long-term metformin users may be at greater risk.
3. Vitamin D Deficiency
Low Vitamin D may accompany fatigue, muscle discomfort, generalised aches, proximal muscle weakness and bone discomfort. People working predominantly indoors in modern Indian cities may have lower 25-hydroxy Vitamin D levels. However, not every tired person has Vitamin D deficiency and not every low result explains the fatigue — the laboratory result must fit the clinical picture.
4. Hypothyroidism
An underactive thyroid is an important diagnosis to consider when fatigue is accompanied by cold intolerance, constipation, dry skin, hair loss, weight gain, slowing of thought or speech, menstrual disturbance, muscle aches or excessive sleepiness. A TSH, often with free T4 when indicated, can clarify the diagnosis.
5. Hyperthyroidism
An overactive thyroid can also cause fatigue due to enormous metabolic stress. Look for heat intolerance, excessive sweating, palpitations, tremor, weight loss despite appetite, anxiety and loose stools. A person can be restless and exhausted simultaneously.
6. Type 2 Diabetes & Glucose Fluctuations
Diabetes commonly presents far more quietly than expected. Fatigue may occur with persistent hyperglycaemia. Patients may also notice excessive thirst, frequent urination, blurred vision, recurrent infections and unexplained weight change. For persistent unexplained tiredness, fasting glucose and HbA1c are often more useful early tests.
7. Post-Infectious Fatigue
Physical endurance may remain reduced for days or weeks after the acute illness has settled. In Indian practice this may follow dengue, COVID-19, influenza, typhoid fever, malaria, infectious mononucleosis or other significant systemic infections.
8. Sleep Disorders
Chronic sleep restriction, insomnia, and obstructive sleep apnoea (OSA) are underdiagnosed causes of fatigue. Think about OSA when there is loud snoring, witnessed breathing pauses, morning headache, dry mouth on waking and daytime sleepiness — particularly in overweight individuals or those with difficult-to-control hypertension.
9. Stress, Anxiety & Depression
Mental health and physical energy are deeply connected. Chronic stress disturbs sleep, appetite and concentration. Depression may enter as fatigue — 'I have no energy', 'everything feels difficult', 'I can't concentrate'. These symptoms deserve the same medical seriousness as hypertension or diabetes.
10. Kidney & Liver Disease
Both chronic kidney disease and chronic liver disease can produce substantial fatigue through anaemia, metabolic disturbance, sleep disorders, chronic inflammation and muscle loss. Persistent unexplained fatigue therefore sometimes warrants renal and liver function testing.
11. Autoimmune & Inflammatory Diseases
Systemic inflammation consumes energy. Fatigue can be prominent in rheumatoid arthritis, SLE, Sjögren syndrome, inflammatory bowel disease, vasculitis and polymyalgia rheumatica — usually with other clinical clues such as joint pain, morning stiffness, rashes or dry eyes.
12. Medicines & Substances
Some antihistamines, antidepressants, anti-anxiety medicines, beta blockers, muscle relaxants and opioids can cause fatigue. Alcohol can impair restorative sleep and produce next-day fatigue. Always discuss your medication list with your doctor before making changes.
⚠️ When Should You Seek Medical Care?
Seek urgent medical attention if you experience any of the following:
- Fatigue with persistent unexplained fever or night sweats
- Fatigue with significant unintentional weight loss
- Fatigue with breathlessness on minimal exertion or difficulty lying flat
- Fatigue with chest discomfort or palpitations at rest
- Fatigue with significant swelling of feet or face
- Fatigue with jaundice or dark urine
- Fatigue with blood in stool, urine or vomit
- Fatigue with confusion or neurological symptoms
- Fatigue that is rapidly worsening without explanation
- Fatigue with enlarged lymph nodes that are persisting
Which Laboratory Tests May Be Considered?
Clinical note: Laboratory tests should be selected by a doctor based on your symptoms, history and clinical examination. Not every person requires all of the tests listed below.
| Test | Why a Doctor May Consider It |
|---|---|
| CBC (Complete Blood Count) | To identify anaemia, and assess haemoglobin, white cell count and platelets |
| Serum Ferritin | Best single test for iron stores — may reveal iron deficiency before anaemia develops |
| Iron Studies (TIBC, serum iron) | To confirm iron deficiency and understand iron metabolism |
| Fasting / Random Blood Glucose | Initial screen for diabetes or hypoglycaemia |
| HbA1c | Reflects average blood glucose over approximately 3 months |
| TSH (Thyroid Stimulating Hormone) | To screen for both underactive and overactive thyroid |
| Free T4 | When TSH is abnormal or thyroid disease is clinically likely |
| Vitamin B12 | Particularly when fatigue is associated with neurological symptoms, anaemia or dietary risk |
| 25-Hydroxy Vitamin D | When Vitamin D deficiency is clinically suspected |
| Kidney Function Tests (KFT) | When renal disease or metabolic disorder is suspected |
| Liver Function Tests (LFT) | When liver disease is suspected or other systemic symptoms are present |
| CRP / ESR | To assess for active inflammation or chronic infection |
Frequently Asked Questions
What is the most common cause of tiredness in women in India?
Iron deficiency anaemia is among the most common identifiable medical causes of persistent tiredness in women, often related to heavy menstrual bleeding or inadequate dietary iron.
Can thyroid disease cause constant fatigue?
Yes. Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) can cause significant fatigue, though through different mechanisms.
Should I take iron tablets if I feel tired all the time?
Not without testing first. Iron supplementation is appropriate when iron deficiency is confirmed. Taking iron when not deficient provides no benefit and may have side effects. A CBC and ferritin test will clarify.
Can stress alone cause extreme tiredness?
Yes. Chronic stress, anxiety and depression can cause profound fatigue. However, important medical causes should not be dismissed without appropriate assessment.
What is the difference between normal tiredness and medical fatigue?
Normal tiredness is typically linked to a busy period and improves after rest, sleep or food. Medical fatigue persists despite adequate rest, may occur without obvious trigger, and may affect work, study or daily activity for weeks or months.
QXL Diagnostic Support
If your doctor recommends blood investigations for persistent tiredness, tests such as CBC, ferritin/iron studies, blood glucose/HbA1c, TSH/free T4, Vitamin B12, Vitamin D, kidney and liver function tests may be considered depending on the clinical picture. QXL Diagnostics provides all these investigations with free home sample collection across Bengaluru.
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Medical Review
Medically reviewed by: Dr. Shantakumar Muruda, MD - Medical Biochemistry; Founder & CEO, QXL Diagnostics Super Speciality Lab, Bengaluru
Last medically reviewed: 2026-09-11
Clinical reference framework:Harrison's Principles of Internal Medicine; Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics; and relevant specialty guidance as clinically appropriate.
Medical Disclaimer: This information is intended for general health education and does not diagnose an individual medical condition. It does not replace consultation, diagnosis or treatment by a qualified healthcare professional. Seek urgent medical attention for severe, sudden or rapidly worsening symptoms or any emergency warning signs described above.