4 Common Causes of Unexplained Fatigue and How to Troubleshoot Them


Low Iron

With symptoms such as fatigue and slight shortness of breath, it's sometimes tough to distinguish iron deficiency from how we feel after a hard workout. But persistent fatigue may indicate that your iron levels are sub-optimal—leading to poor performance and higher levels of fatigue. 

Diagnosing Iron Deficiency

Scheduling a simple blood test with your physician can help you determine if low iron is the cause of your fatigue. You'll want to have your doctor test for hemoglobin (Hg), hematocrit (Hct), iron (Fe), total iron binding capacity (TIBC) and ferritin.  If you are anemic, your hemoglobin and hematocrit, which measures of your red blood cell count, are low. If you have an iron deficiency, your ferritin, which is a measure of your stored iron, is low, and your total iron binding capacity is high, indicating there is extra room to bind more iron. For most runners in training, you'll want to make sure that ferritin number is over 30ng/ml for women and over 40ng/ml for men. 

Treating Iron Deficiency

If you do find you have an iron deficiency, your doctor will likely recommend supplements. You can take an iron supplement of ferrous sulfate in either liquid or pill form. You can also supplement iron through your diet; dark leafy greens, lean meat, egg yolks, legumes and oysters are good sources of iron.  It may take several weeks of supplementation to rebuild your iron stores, but once you do, you should find your fatigue subsides. 

Epstein-Barr Virus

Though these two diseases may seem quite unrelated, lingering fatigue can be a red flag for each.  I didn't expect to hear about the Epstein-Barr virus (otherwise known as "mono") again after contracting it as a college student, but after a terrible training season where I kept getting slower and more exhausted, I had the doctor do some blood work and boom: She found the virus had reactivated in my body.  Nine out of 10 adults will have contracted EBV in their lifetime, and it's common for the virus to lie dormant for years only to reactivate at a future time.  EBV can have symptoms such as swollen lymph nodes, fever, enlarged spleen and potentially a rash, but many adults present with only one symptom: fatigue. 

Diagnosing EBV

An EBV infection or reactivation can be confirmed through your doctor by ordering a blood test that detects antibodies. 

Treating EBV

Some doctors may prescribe antiviral drugs to help with the symptoms, but rest and time are the main treatments required. Most people feel better in four to six weeks, but some cases require a few months to recover. 

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