Sleep is essential for overall well-being and vital to maintaining health. As a complex process with various stages and cycles, sleep can be evaluated using polysomnography and consumer sleep trackers, although the latter are less accurate for monitoring sleep stages. Sleep needs and patterns evolve throughout life, from infancy to older adulthood, with adults ages 18 to 64 years typically requiring 7 to 9 hours per night for optimal health. Insufficient sleep is associated with an increased risk of chronic conditions, including cardiovascular disease, diabetes, and obesity, and a weakened immune system. It also impairs cognitive function, decreases productivity and quality of life, and increases the risk of motor vehicle crashes. Sleep deprivation is closely tied to mental health issues, such as anxiety and depression. Although napping or sleep banking may offer temporary relief from sleep deprivation, they cannot be a substitute for regular, high-quality sleep. Consistently sleeping more than 9 to 10 hours per night, known as hypersomnia, has been linked to health issues including weight gain, mental health conditions, and cardiovascular disease. Prioritizing appropriate sleep duration and quality is essential for physical and mental health, helps prevent a variety of health issues, and promotes better daily functioning.
Case 1. BT is a 46-year-old man who comes to your office for a health maintenance examination. His blood pressure is 144/88 mm Hg, and body mass index is 28.5 kg/m2. The rest of his physical examination and results of routine laboratory tests are unremarkable. He reports feeling more fatigued and less motivated to exercise in the past year. He likes to watch videos on his tablet until late at night and usually sleeps about 6 hours per night. He says he used to be able to function well on little sleep, but it seems lack of sleep is now catching up with him.
Normal Sleep Patterns
DEFINITION
Sleep is a complex behavioral and physiologic process that is categorized into two states: non–rapid eye movement (NREM) sleep, which begins with a wake stage and then is further subdivided into three stages (N1, N2, N3), and REM sleep. Sleep plays a critical role in immunity, hormonal regulation, memory consolidation, mental well-being, and cardiovascular health.1
SLEEP STAGES AND CYCLES
Of the five stages (wake, N1, N2, N3, and REM), about 75% of sleep is spent in the NREM stages, with N2 being the predominant stage.2 A normal adult sleep pattern includes four to six sleep cycles each night. Typically, the cycle duration lengthens as the night progresses. The first sleep cycle is the shortest, lasting 70 to 100 minutes, whereas later cycles last about 90 to 110 minutes.2 The typical sleep sequence in a cycle is N1, N2, N3, N2, and REM, but REM sleep precedes the N3 stage occasionally.
In the first stage of NREM sleep, the wake stage, a person is still awake; further characterization depends on whether their eyes are open or closed. On electroencephalography (EEG), the initial predominant recording is beta waves, and as a person becomes drowsier and closes their eyes, the recording transitions to an alpha wave predominance.3
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