According to a recent survey of over 20,000 people by researchers at Radboud University in the Netherlands, about 30 percent of visits to doctors involve complaints about being tired all the time. But fatigue causes can be tricky, as our post explains.

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Fatigue is a common symptom in people with medical conditions like cancer and diabetes, mood disorders like depression and anxiety, and even in people who are otherwise “healthy.” Yet despite how prevalent it is, medical researchers still do not completely understand what happens in the body to cause fatigue. They hypothesize that fatigue typically results from a complex set of interacting factors, rather than a single cause. A number of these factors have now been identified and studied. Here we take a look at five of the most common fatigue causes.

Fatigue Causes: #1—Stress

Chronic stress often leads to dysregulation of the body’s stress systems and is a common underlying cause of chronic fatigue._[1] The popular term “adrenal fatigue,” with its focus on the adrenal glands and cortisol production, is often used to describe this unhealthy reaction to chronic stress.

Adrenal fatigue, however, does not take into account the complex system of interconnected events involved in the stress response. The brain, nervous system, endocrine (hormonal system), and immune system are all key components, as are adrenal glands. In particular, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) are the primary regulatory centers. Fatigue is a common consequence of excessive, prolonged, or inadequate regulation of these stress response systems._[2] (Find tips on beating stress here.)

Fatigue Causes: #2—Poor Nutrition/Digestion

Nutrition and digestive issues such as nutritional deficiencies, food allergies, blood sugar dysregulation, and excessive permeability in the lining of the intestines can all cause fatigue. Those suffering from fatigue are commonly eating a poor-quality diet (low in fruits and vegetables; deficient in vitamins, minerals, and phytonutrients; excessive in high-glycemic, high-fat, high-inflammatory foods).

In addition, fatigue sufferers have been found to have more digestive symptoms linked to altered intestinal bacteria (such as not enough acidophilus) and abnormal function of the intestinal lining (a.k.a. “leaky gut”) compared to non-fatigued individuals._[3] (Learn more about leaky gut syndrome here: 5 Top Reasons You Might Have Leaky Gut Syndrome and Feel Tired All the Time or Have Depression Symptoms.

Fatigue Causes: #3—Hormone Imbalances

Fatigue may result from low or imbalanced levels of common hormones such as thyroid, testosterone, estrogen, and progesterone. Low thyroid hormone levels resulting from autoimmune thyroid disease is one of the most common hormone-related disorders, and fatigue is the main symptom of hypothyroidism. In women, menopausal symptoms such as night sweats are notorious for causing fatigue _[4], while in men testosterone deficiency as a cause of fatigue is now being recognized more than ever before._[5]

Fatigue Causes: #4—Anxiety and Depression

Mood disorders such as depression and anxiety, the most common mental health disorders in the United States, either cause or are strongly associated with fatigue and daytime sleepiness. The majority of people with depression suffer from fatigue.

In fact, fatigue is one of the most common symptoms of depression that patients complain to their healthcare providers about. In one recent study, more than 90 percent of patients with major depression had severe fatigue despite the fact that more than 80 percent of these patients were already taking antidepressant medications._[6] Depression-related fatigue is often associated with impaired concentration, irritability, and reduced productivity.

Fatigue Causes: #5—Sedentary Lifestyle and Deconditioning

Being highly sedentary increases the risk of chronic fatigue. Not getting enough exercise and physical activity causes deconditioning of the body’s musculoskeletal and cardiovascular systems and depresses mood, all of which lead to fatigue. Studies show that the more regular physical activity you get, the more likely you are to feel energetic.

Exercise has been shown to help reverse fatigue associated with all kinds of medical conditions, from cancer to autoimmune diseases to depression._[7] (Find more reasons to exercise here.)

To overcome fatigue, break the cycle of a sedentary lifestyle and start a regular exercise program

So if you’re “feeling sleepy all the time,” which of the above fatigue causes might apply to you? You may need to engage the services of a qualified integrative physician to help you sort through the various fatigue causes, run the necessary tests, and develop a strategy that deals with the root cause of your persistent tiredness. Understanding the root causes, as we hear so often, is the first step to recovery.

[1] Silverman MN, Hein CN, et al. Neuroendocrine and immune contributors to fatigue. PM R. 2010 May; 2(5): 338-346.
[2] Papadopoulos AS, Cleare AJ. Hypothalamic-pituitary-adrenal axis dysfunction in chronic fatigue syndrome. Nat Rev Endocrinol. 2011 Sep 27;8(1):22-32.
[3] Lakhan SE, Kirchgessner A. Gut inflammation in chronic fatigue syndrome.  Nutrition & Metabolism 2010, 7:79.
[4] Alexander JL, Neylan T, et al. Assessment and treatment for insomnia and fatigue in the symptomatic menopausal woman with psychiatric comorbidity. Expert Rev Neurother. 2007 Nov;7(11 Suppl):S139-55.
[5] Moncada I. Testosterone and men’s quality of life. Aging Male. 2006 Dec;9(4):189-93.
[6] Ferrentinos P, Kontaxakis V, et al. The Fatigue Questionnaire: standardization in patients with major depression. Psychiatry Res. 2010;177(1):114–119.
[7] O’Connor PJ, Puetz TW. Chronic physical activity and feelings of energy and fatigue. Med Sci Sports Exerc. 2005 Feb;37(2):299-305.

Originally published in 2012, this post is regularly updated.