What Are the Causes of Feeling Tired a Lot?

It's normal to feel tired sometimes. However, if fatigue is persistent and unresolved by rest and activity, it may be related to an underlying medical condition such as chronic fatigue syndrome. If you receive adequate sleep, eat well and get plenty of exercise but still experience constant tiredness, consult your doctor to determine the possible cause.

Chronic Fatigue Syndrome

According to the University of Maryland Medical Center, chronic fatigue syndrome (CFS) is difficult to define and diagnosis. Patients must meet a variety of criteria in order to be officially diagnosed with CFS. These include persistent exhaustion that is unrelieved by sleep or activity and a variety of additional symptoms, such as sore throat, muscle pain and tender lymph nodes. Fatigue must persist for at least six months before diagnosis can be made, and additional symptoms must occur after the onset of fatigue.

Lack of Sleep

If your fatigue is not serious enough to be diagnosed as CFS, take careful note of your sleeping habits. It may seem obvious, but many adults do not receive adequate sleep, resulting in constant tiredness. Inadequate sleep can also cause additional undesirable symptoms. According to Harvard Medical School, sleep deficiency may cause weight gain, decreased immunity, cardiovascular problems, lack of focus and irritability. For optimal health, get at least eight hours of quality sleep each night.


Anemia is defined as a deficiency of red blood cells and usually results in constant, unresolved tiredness. Other symptoms of anaemia include irregular heartbeat, headache, lack of focus, dizziness and shortness of breath. Anemia is usually diagnosed with the help of a complete blood count (CBC), which tells doctors the exact amount of red blood cells and haemoglobin in your blood. Since anaemia can be caused by a variety of factors, treatment depends on the underlying cause. For example, if your anaemia is related to iron deficiency, you will need to take an iron supplement.

Vitamin Deficiency

Constant fatigue may also be related to a vitamin deficiency. A variety of vitamins are necessary for overall health and vitality, and some are particularly crucial for energy levels. Vitamin D deficiency, for example, may cause chronic fatigue as well as other symptoms like chronic pain and muscle weakness. Vitamin B12 deficiency is a common cause of anaemia, according to American Family Physician. If you suspect a vitamin deficiency, consult your doctor about taking a daily supplement.

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About the Author

Nicole Crawford is a NASM-certified personal trainer, doula and pre/post-natal fitness specialist. She is studying to be a nutrition coach and RYT 200 yoga teacher. Nicole contributes regularly at Breaking Muscle and has also written for "Paleo Magazine," The Bump and Fit Bottomed Mamas.