In recent years the never-ending quest for more time has led some people to attempt to make their time spent sleeping more “efficient” by eliminating the stages of sleep referred to as “non-rapid eye movement” (NREM) sleep. Advocates of these experimental sleeping strategies say that NREM sleep, which accounts for the bulk of time that an individual spends sleeping in a night, is nonessential and can be dispensed with without affecting one’s waking performance. However an examination of research into NREM sleep suggests that this part of the sleep cycle plays a key role in the body’s healing process, growth, hormone balance, and memory consolidation.
A single sleep cycle can be broken into five distinct phases, the first four of which are considered to be NREM sleep. In these stages the body starts with lighter sleeping in stage one and subsequently moves into deeper states of relaxation. The breathing slows, blood pressure drops, and muscles relax, especially in stages three and four which are collectively known as “slow wave sleep” or “SWS.” After stage four the body moves into REM sleep (also referred to as “paradoxical sleep”) which is characterized by brain activity, darting eyes, and dreaming. On average a single sleep cycle takes about 90 minutes.
Websites such as KratosGuide.com, LifeHacker.org, and StevePavlina.com claim that REM sleep is the only type of sleep necessary to survive and function normally. According to them the other four NREM sleep stages are a waste of valuable time. This rationale is what persuades some people to undertake radical self-experimentation with restricting their sleep cycles. Extreme cases are the “Ubermen” people who strive to sleep for only two hours each day with the rationale that these two hours will be restricted to only the essential REM sleep
Is NREM sleep really a waste of time? In response to the claims made by the online body-hackers some sleep experts such as Dr. Wozniak have come out with strong recommendations against what they consider to be an extremely unhealthy practice. Key among the list of objections to the Uberman lifestyle is the faulty assumption that the six hours of NREM sleep that the average adult gets in an eight hour night are a waste of time.
To begin, the time spent in NREM sleep is essential for the body’s healing process. Repairs to damaged tissue as well as growth in muscles and bones all occur during NREM sleep. Researchers also have discovered that after contracting an infection, animals increase their relative time in NREM sleep as a way to combat the invading pathogens. SWS, the “deepest” stages of sleep, were also found to be critical for gaining feelings of refreshment after slumber.
In addition, NREM sleep is a time when important hormones are secreted into the body. Growth hormone in particular is released during the deep stage three and stage four phases, making NREM especially critical to the health of developing adolescents. Other important hormones involved in reproductive health such as luteinizing hormone (LH) are also secreted during this time.
NREM sleep is also critical for maintaining insulin sensitivity in humans. Experimental subjects who were deprived of SWS but maintained their normal hours of sleep showed significantly lower insulin sensitivity and reduced glucose tolerance—both conditions that are linked to an increased risk of developing diabetes.
Finally, NREM sleep has been demonstrated to play an important role in memory consolidation. This is especially true with respects to recalling motor skills and visual memory. Experiments with restricting NREM sleep have found that the low levels of acetylcholine that are propagated during slow wave sleep are critical for consolidating such declarative (aka explicit) memory.
The evidence discussed here is only a small snippet of the wealth of information available on the role that NREM sleep plays in human health. Therefore before undertaking any extreme overhauls of one’s sleep schedule, a critical thinker would do well to consider whether such an endeavor would be worth the effort.
By Sarah Takushi
Dr. Wozniak 1
Dr. Wozniak 2
National Sleep Foundation
Physiology & Behavior