Why Do We Need Sleep?

Along with food and water, sleep is one of the human body's most important physiological needs—we cannot live without it. Extended sleeplessness (i.e., lack of sleep for longer than a few days) has severe psychological and physical effects. Research on rats has found that a week of no sleep leads to loss of immune function, and two weeks of no sleep leads to death.

Despite its clear importance to psychological and physiological functioning, researchers have struggled for centuries to answer the question of why we sleep. On the surface, we know that sleep helps our body recuperate from a day's physical exertions. It also aids in recovery from illnesses and infections. We also know that extended sleeplessness can lead to hallucinations, delusions, loss of immune function, and in extreme cases, death. Modern research has also uncovered that sleep has a major role in maintaining our mental and emotional health.

Recently, neuroscientists have learned that at least one vital function of sleep is related to learning and memory. New findings suggest that sleep plays a critical role in flagging and storing important memories, both intellectual and physical, and perhaps in making subtle connections that were invisible during waking hours.

Though scientists are still learning about the concept of basal sleep need (just how much sleep we need), research has demonstrated that sleeping too little can inhibit your productivity and your ability to remember and consolidate information. Lack of sleep can also lead to serious health consequences, jeopardizing individual safety and the safety of others.

For example, sleep deprivation is related to:

• higher rates of motor vehicle accidents;
• higher BMI, an increased likelihood of obesity, and increased risk of diabetes and heart problems;
• higher risk for depression and substance abuse;
• decreased attention, slower reaction times, and the inability to remember new information.

When we do not sleep enough, we accumulate a sleep debt. Sleep debt occurs as the result of not getting enough sleep, and a large debt causes mental, emotional, and physical fatigue. Sleep debt results in diminished abilities to perform high-level cognitive functions.

How Much Sleep Do We Need?

The amount of sleep we need varies depending on multiple factors including age, physical condition, psychological condition, and energy exertion. Therefore, sleep requirements depend entirely on the individual. Just like any other human characteristic, the amount of sleep people need to function best differs among individuals, even those of the same age and gender. For example, a pregnant woman will need more sleep than a healthy woman of the same age, an adult with a cold will need more sleep than one who is well, and an individual with depression may require more sleep than a non-depressed person.

Though there is no magic sleep number, there are general rules for how much sleep certain age groups need. For instance, children need more sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as a child ages. A newborn baby spends almost 9 hours a day in REM sleep. By the age of five, only slightly over two hours is spent in REM. Studies show that young children need about 10 to 11 hours of sleep, adolescents need between 8.5 and 9.25, and adults generally need between 7 and 9 hours.

Effects of Sleep Deprivation  

Research has uncovered a number of ways that a lack of sleep affects our well-being. Sleep deprivation negatively affects brain chemistry, growth, healing, attention, memory, and the ability to operate machinery, among other things. Sleep deprivation can cause both physical and mental illness, such as diabetes, depression, and psychosis, and in extreme cases, it can cause hallucinations and death. 

Sleep Deprivation on the Brain and Body

Numerous studies have demonstrated that sleep deprivation can adversely affect brain growth and cognitive functions. fMRI studies performed on sleep-deprived subjects show that regions of the brain's prefrontal cortex, an area that supports mental faculties such as working memory and logical reasoning, displayed more activity in sleepier subjects. The results implied that sleepier subjects had to work harder than well-rested subjects to accomplish the same task, indicating the need to compensate for adverse effects caused by sleep deprivation.

The link between sleep deprivation and psychosis has been well-documented. In 2007, a study at Harvard Medical School and the University of California at Berkeley revealed, using MRI scans, that sleep deprivation causes the brain to become incapable of putting an emotional event into the proper perspective and incapable of making a controlled, suitable response to the event. 

The negative effects of sleep deprivation on alertness and cognitive performance suggest decreases in brain activity and function, primarily in the thalamus, a structure involved in alertness and attention, and in the prefrontal cortex, a region sub-serving alertness, attention, and higher-order cognitive processes.

Sleep deprivation has also been found to inhibit stress reactions, body functions such as digestion, the immune system, mood, sex, and energy usage, while also suppressing growth hormones. Sleep deprivation has also been shown to slow the healing process, and has been implicated in weight gain and type-2 diabetes.