Other Medical Conditions - What Causes Fatigue: Chronic Fatigue

Content provided by the Faculty of the Harvard Medical School

Other medical conditions

Fatigue is a symptom of numerous illnesses, from minor infections such as colds to serious diseases such as cancer and heart disease. With the following illnesses, fatigue is one of the main symptoms. Some of these disorders cause fatigue directly, by sapping the body's energy supply; others do so indirectly, as the immune system attempts to fight off the illness. Either way, once you get treatment or the infection subsides, your energy level should rebound.

Chronic infections

Unlike acute infections such as a cold or flu, which go away in a week or two, chronic infections can last for months or years. During that time, the body expends large amounts of energy trying to overcome the infection, which can leave a person feeling lethargic and weak. The immune system mounts an attack on the infection by unleashing a group of chemicals called cytokines. The cytokines are known to cause fatigue, possibly by increasing the production of stress hormones. Chronic infections that cause particularly severe fatigue include tuberculosis, Lyme disease, and any form of hepatitis. Each of these illnesses has effective treatments, and once treated, most people find that their energy level improves.

Anemia

Anemia is a condition in which the blood has too few red blood cells and, thus, low levels of hemoglobin, the protein inside red blood cells that delivers oxygen to tissues throughout the body. Anemia can lead to fatigue because the cells of your body need oxygen both to create ATP and to liberate energy stored as ATP. Thus, a shortage of oxygen can mean a shortage of energy (see "Food and energy").

A simple blood test can detect anemia.

Anemia is a common condition, especially among women, and is most often caused by iron deficiency. This type of anemia affects about 9%–12% of women under age 70. But iron-deficiency anemia typically does not cause fatigue unless it's severe. Another form of anemia, known as pernicious anemia, results from a deficiency in vitamin B₁₂, which causes the bone marrow to produce red blood cells that are larger and shorter-lived than normal red blood cells, reducing the number of oxygen-carrying cells.

Anemia is easily diagnosed with a blood test, and for most types, there are effective treatments. For example, anemia caused by a deficiency in iron or vitamin B₁₂ can be cured with supplements of those nutrients. Generally, supplements are taken orally, but if your deficiency stems from your stomach's inability to absorb vitamin B₁₂, it can be given by injection. If iron-deficiency anemia is the problem, your fatigue should lift within three to six weeks of beginning iron supplements.

Kidney disease

Various types of diseases that damage the kidneys may indirectly cause fatigue by reducing production of erythropoietin (EPO). This hormone stimulates the bone marrow to make and release red blood cells. The kidneys produce most EPO in your body, so if kidney function is impaired, you could develop anemia and the accompanying fatigue.

Your doctor can diagnose most kidney diseases with simple blood and urine tests. In many cases, your fatigue will be remedied once the underlying kidney problem is treated. If you have chronic kidney disease, the first step in treating anemia is usually iron supplements, which enable the EPO you produce naturally to promote production of red blood cells. If this is not sufficient to keep your hemoglobin levels normal, you may be eligible for injections of a synthetic form of EPO. Talk with your doctor about which options are best for you.

Congestive heart failure

Congestive heart failure occurs when the heart is unable to pump enough blood to meet the body's needs. Insufficient blood flow through the brain, kidneys, and muscles can cause weakness and fatigue. Compounding the problem, the failing heart works extra hard to pump blood, using up more than its share of energy.

Your doctor can detect congestive heart failure through a physical examination and diagnostic tests. The disease can be controlled by a combination of appropriate medications and lifestyle changes, such as avoiding salty foods. Depending on the person's age and the severity of the condition, treatment can, to some degree, relieve the fatigue.

Hormonal disorders

Hormones are chemicals produced by glands, and are responsible for regulating a wide variety of physical functions, including those associated with digestion, reproduction, and blood circulation. Unusually high or low levels of specific hormones are responsible for several disorders that can be accompanied by fatigue, including hypothyroidism, diabetes, and Addison's disease.

Hypothyroidism. This condition occurs when the thyroid gland does not produce enough thyroid hormone. If you have hypothyroidism, you may feel lethargic because your metabolism (the breakdown of food for energy) slows down. Almost 10 million people in the United States have hypothyroidism. The condition be­comes increasingly common with age, and it's more common in women than in men. About one in five women over age 65 have some degree of hypothyroidism.

Hypothyroidism has several causes. The most common is Hashimoto's thyroiditis, an autoimmune disease in which the immune system attacks the cells of the thyroid, causing inflammation and cell destruction. Hypothyroidism can be diagnosed with blood tests that measure your levels of various thyroid hormones. The most commonly measured of these is thyroid-stimulating hormone (TSH). Hypothyroidism usually is treated with thyroid hormone replacement, which provides synthetic versions of natural thyroid hormones.

Interestingly, particularly in people over age 60, too much thyroid hormone (a condition called hyperthyroidism) also can produce fatigue — along with jitteriness and weight loss despite a good appetite. This condition, called "apathetic hyperthyroidism," is often overlooked by doctors. It also can be diagnosed by the TSH test.

Diabetes. Blood sugar (glucose) provides energy to cells, but first it must get inside the cells to be converted to a usable energy form. The pancreas makes insulin, which helps transport sugar into cells. In type 1 diabetes, the pancreas doesn't make enough insulin. In type 2 diabetes, the pancreas initially makes more than enough insulin, but the cells are resistant to it. In either type of diabetes, insufficient sugar gets into the cells, impairing their ability to generate energy. Lack of physical and mental energy is among the many symptoms of diabetes.

Diabetes can be diagnosed with a blood test that measures levels of glucose in the blood. Although there's no cure, a variety of treatments can help control its symptoms, including medications that supply added insulin or increase the body's insulin sensitivity, and lifestyle changes, particularly daily exercise and weight loss.

Addison's disease. This rare hormonal disorder occurs when the adrenal glands don't make enough of the hormones cortisol and aldosterone. Its most common cause is an autoimmune disease in which the immune system produces antibodies that attack and destroy the outer layer of the adrenal glands, reducing hormone production. Symptoms develop gradually and include tiredness and weakness, as well as loss of appetite, nausea, and dizziness, among others. If severe or untreated, the disease can be fatal. The treatment is replacement hormones.

Multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease in which the body mistakenly attacks myelin, the substance that covers nerve fibers. The symptoms vary from one individual to the next and range from mild to severe. The most severe symptoms are weakness, paralysis, and blindness. However, symptoms of MS can come and go. Although many people recover completely between attacks or "flare-ups" of the disease, others suffer a progressive loss of function. The most debilitating part of MS can be severe fatigue. Even in the absence of muscular weakness, there is central fatigue, characterized by difficulty concentrating and general exhaustion, which makes undertaking any activity difficult.

The cause of MS is unknown, and there's no cure. But several medications may reduce the symptoms, including the fatigue. In particular, the antiviral agent amantadine (Symmetrel) may improve MS-related fatigue. Another option worth looking into is modafinil (Provigil). Although the FDA approved modafinil only for the treatment of daytime sleepiness from narcolepsy, obstructive sleep apnea, or shift work, it is also effective at treating MS-related fatigue and can be prescribed for that purpose.

Cancer

Many different types of cancer can cause loss of appetite and energy, even before the cancer causes other symptoms. Most likely, the fatigue is caused by increased levels of cytokines — chemicals made when the immune system is fighting an infection or a cancer. While the likelihood of cancer is fortunately small in a person with a recent loss of appetite and energy, it is likely enough that you should contact your doctor about it. This is particularly true if you are losing weight without trying to, or have other worrisome symptoms such as unexplained fevers, new pain someplace in your body, unusual lumps in your breast or testicles, or swelling of the lymph nodes in your neck, under your arms, or in your groin.

Last updated:	January 23, 2007