THINK about the times when you stifled a yawn and reached for yet another of your special energy drinks. What happens when the fatigue just will not go away? Call it what you wish — tiredness, lack of energy, fatigue — the fact is that this often overlooked and very common complaint is frequently a warning sign of ill health.

If you are always tired and your fatigue does not go away after resting, your body may be alerting you to an undiagnosed illness.

It could be:

Anaemia

This is a potentially life threatening condition which occurs when the amount of oxygen carrying haemoglobin falls below normal levels. The body is literally forced to work harder to get oxygen to its vital organs. There are a number of possible causes — deficiencies of iron, Vitamin B12 and folic acid; heavy periods, worm infestation, kidney disease and poor nutrition.

You may notice that you tire easily, feel out of sorts, and that a routine task such as cooking breakfast requires more effort.

Depression

This is one of the most common mental illnesses. Women are more prone to the development of depression. In some persons the fatigue is debilitating, lasting all day. Others feel sluggish, even after plenty of rest. You may find yourself sleeping too much or too little. There are other symptoms such as irritability, hopelessness, changes in eating habits, lack of interest in previously pleasurable activities such as sex, relationships or hobbies.

Diabetes

Type 1 and Type 2 diabetes occur because the body is not effectively using or producing insulin, a hormone that helps cells to absorb glucose, a fuel for the body. As a result there is a build up of glucose in the blood. The cells are then unable to function properly. Over time the high glucose levels damage the eyes, heart, kidneys and nerves. The fatigue associated with diabetes can be subtle. Other symptoms include frequent infections, frequent urination, excessive thirst and hunger, weight loss and blurred vision.

Chronic kidney disease

This occurs when your kidneys are not filtering enough waste from your blood, causing a build up of toxins. High blood pressure and diabetes are the two most common causes of kidney disease. This condition can, of itself, cause high blood pressure, anaemia, nerve damage, poor nutritional health and weak bones. Persons suffering from kidney disease easily tire and often complain of feeling out of breath. This fatigue is caused by anaemia. Other symptoms include weight loss, loss of appetite, vomiting and swelling of the feet.

Thyroid disease

Hypothyroidism

In this condition, the thyroid gland is producing too little of the thyroid hormone. Since the main purpose of the thyroid hormone is to run the body's metabolism, people with this condition will have symptoms associated with a slow metabolism. Left untreated, hypothyroidism can lead to high cholesterol levels, heart disease, muscle weakness and infertility. Other symptoms include weight gain, constipation, hair loss, rough, coarse skin, memory loss, irritability, depression, muscle cramps and aches, intolerance to cold and loss of libido.

Hypothyroidism may affect menopausal women. The fatigue makes you feel weak and sluggish with muscle aches, especially in colder weather.

Hyperthyroidism

This occurs when the thyroid gland produces too much hormone. Untreated hyperthyroidism can lead to a life-threatening irregular heartbeat. Unexplained weight loss, restless sleep, tremor, frequent bowel actions, heat intolerance and warm, sweaty skin are associated with this disease.

In this case, the fatigue feels like muscle weakness, which is very noticeable when you are exercising.

These are not the only causes of fatigue. Other causes include chronic fatigue syndrome, sleep apnoea, mononucleosis, hepatitis C and fibromyalgia.

If you are feeling tired, it may be a sign that something is going wrong with your body. You need to visit your doctor for a physical examination, appropriate investigations and treatment.

Dr Jacqueline Campbell is a family physician and author of A Patient's Guide to the Treatment of Diabetes Mellitus.