1. Causes of Fatigue Slideshow Pictures
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Author:

Michael B. Russo, MD

Coauthor:

Shehnaz Shaikh, MD

Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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Because the function of sleep has not been fully determined, the exact number of hours that a person should sleep is unknown. Some persons claim to work optimally with only 3 to 5 hours of sleep per night, while some admit needing at least 8 hours of sleep per night (or more) to perform effectively. Therefore, sleep deprivation is best defined by group means and in terms of the tasks impaired.

In tasks requiring judgment, increasingly risky behaviors emerge as the total sleep duration is limited to 5 hours per night. The high cost of an action is seemingly ignored as the sleep-deprived person focuses on limited benefits. These findings can be explained by the fact that metabolism in the prefrontal and parietal associational areas of the brain decrease in individuals deprived of sleep for 24 hours. These areas of the brain are important for judgment, impulse control, attention, and visual association.

Sleep deprivation is a relative concept. Small amounts of sleep loss (for example, 1 hour per night over many nights) produce subtle cognitive impairment, which may go unrecognized. More severe restriction of sleep for a week leads to profound cognitive deficits, which may also go unrecognized by the individual. If you feel drowsy during the day, fall asleep for very short periods of time (5 minutes or so), or regularly fall asleep immediately after lying down, you are probably sleep-deprived.

Many studies have made it clear that sleep deprivation is dangerous. With decreased sleep, higher-order cognitive tasks are impaired early and disproportionately. On tasks used for testing coordination, sleep-deprived people perform as poorly as or worse than people who are intoxicated. Total sleep duration of 7 hours per night over 1 week has resulted in decreased speed in tasks of both simple reaction time and more demanding computer-generated mathematical problem solving. Total sleep duration of 5 hours per night over 1 week shows both a decrease in speed and the beginning of accuracy failure.

Total sleep duration of 7 hours per night over 1 week leads to impairment of cognitive work requiring simultaneous focus on several tasks. In driving simulations, for example, accidents increase progressively as total sleep duration is decreased to 7, 5, and 3 hours per night over 1 week. Driver fatigue is responsible for an estimated 100,000 motor vehicle crashes and 1,500 deaths each year, according to the National Highway Traffic Safety Administration.

Since drowsiness occurs just before falling asleep, driving while drowsy often leads to disaster.

According to the National Sleep Foundation "If you have trouble keeping your eyes focused, if you can't stop yawning, or if you can't remember driving the last few miles, you are probably too drowsy to drive safely." It is important to know that caffeine and other stimulants cannot overcome the effects of severe sleep deprivation. Therefore, if you find yourself driving in a sleep-deprived state, it is imperative that you find a safe place to stop and catch up on your sleep before continuing safely on your way.

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