He was sitting in one corner of the waiting room in my clinic. He barely talked, and avoided eye contact with people around him.

He was 36 years old and had been a construction worker, a housepainter, and an auto-body worker at different times of his life. At 18, he had experienced what sounded like a severe viral illness with high fever, fatigue, severe muscle pain, sweating and headaches. His main complaint today was fatigue, exhaustion and muscle ache.

On examination, his blood pressure was normal. In fact, he had no abnormal physical findings. On further investigation, all labs including a complete blood count, hemoglobin, electrolytes, sedimentation rate and thyroid tests were normal. It was only at his next visit to the office that he told me that he had been admitted to a hospital at 30 years of age for severe depression.

Chronic tiredness and fatigue are amongst the more common complaints that bring people to their doctors. They use phrases such as "I lost my zip," "I am beat" or "I am dragging." A common cause of tiredness is our modern lifestyle and associated factors such as overweight, over-eating and not exercising enough.

It is futile to attempt a "quick-fix" energy spurt from stimulants such as caffeine and sugar: these merely leave you feeling more fatigued over time. Conversely, healthy eating habits and regular exercise are effective strategies to combat fatigue.

In a recent study, about 60 percent of women indicated that they get only a few nights of adequate sleep a week. Lack of sleep is big contributor to fatigue, and it is thus important to avoid caffeine and alcohol in the hours leading up to bedtime.

The American College of Physicians suggests that the best prescription for ordinary, garden- variety tiredness is regular, vigorous exercise at least three hours before you go to bed.

Several factors limit optimal physical activity in individuals with chronic fatigue:

• There may be a lack of motivation in beginning the activity
• The person often tires easily once the activity begins
• Mental fatigue and impaired concentration and memory impact both initiation and completion of an activity

Importantly, fatigue that lasts longer than two weeks should prompt a visit to a doctor. There are multiple causes to consider after eliminating the most common causes of fatigue. According to Sandra Fryhofer, MD, from the Emory University School of Medicine in Atlanta, common suspects are as follows:

• Anemia: This is a common cause of fatigue and very easy to check with a simple blood test. A decrease in the oxygen-carrying capacity of blood from a decrease in hemoglobin levels causes fatigue. This is particularly a problem for women, especially those who have heavy menstrual periods.
• Deficiencies in key nutrients, including potassium: Again, this is easily checked with a blood test.
• Thyroid problems: Low levels of thyroid hormone (hypothyroidism) can cause fatigue, weakness, lethargy, weight gain, depression, memory problems, constipation, dry skin, intolerance to cold, coarse and thinning hair, brittle nails, or a yellowish tint to skin. High levels of thyroid hormone (hyperthyroidism) can also cause fatigue. This is also associated with weight loss, increased heart rate, intolerance to heat, sweating, irritability, anxiety, muscle weakness and sometimes thyroid enlargement.
• Diabetes: If you feel fatigued and have blurred vision, weight problems, frequent urination, increased thirst and a large appetite, you should get checked for diabetes with a blood test.
• Depression: Depression may be an issue if exhaustion is associated with sadness, loss of appetite and a lack of pleasure in activities that one previously enjoyed.
• Sleep apnea: If one does not feel fresh in the morning, has excessive daytime sleepiness and possibly snores, it is important to check for sleep apnea.
• Heart disease: Tiredness can be a sign of undiagnosed heart disease. Getting fatigued or feeling winded after exercising can be a red flag for heart trouble.
• Other medical conditions such as liver failure, kidney failure or restless leg syndrome can cause fatigue.
• Many prescription and nonprescription medicines can cause weakness or fatigue.
• Finally, the use or abuse of alcohol, caffeine, or illegal drugs can cause fatigue.

Coming back to my patient, I revisited his medical history. It was almost certain that his fatigue was related to depression. I started him on an anti-depressant, and recommended a healthier lifestyle and adequate sleep. Two weeks later, he reported that he felt much better, was more motivated and had an improved appetite.

Many people suffer from depression. They long to live a life of purpose and fulfillment but constantly live a life of cold fear, boredom, or hopelessness. Watch for the red flags of depression and contact your doctor if you notice any such symptoms.

Sidhartha Pani, MD, is a physician trained in internal medicine and nephrology. He is associated with Emerson Hospital in Concord, Mass. He also has his own practice in Sudbury, Mass. A resident of Brookline, Mass., he enjoys traveling, reading and painting. He is a regular contributor to the Emerson discussion board and is keenly interested in preventive health. He can be contacted at SPani@emersonhosp.org.