To Sleep, or Not to Sleep? That is The Question

Category : Lifestyle Disease Connection
Author : Dr. Namita Tyagi

Disclaimer: This blog is for informational purposes only and should not be construed as medical advice. The reader should consult their health care provider before self diagnosing or altering their treatment based on anything they read here.

Humans spend a third of their lives sleeping, have you ever wondered why? Evolutionarily speaking, it makes no sense at all. During sleep our ancestors were not foraging for food, looking for a mate and above all, were extremely vulnerable to predation. Yet, mother nature did not select against this seemingly unnecessary physiological requirement. It is now evident that sleep enhances every single physiological function in our bodies and brains, while a lack of adequate sleep adversely affects them.

The WHO has stated that humans require an average of 8 hours of sleep each day for optimal health. Sadly the actual amount of sleep modern humans achieve has been decreasing year after year, particularly in the industrialized nations. The demands placed by modernity on our time have meant that this vital physiological function is being squeezed out incrementally. The average sleep duration in Japan is currently the lowest in the industrialized world, at 6 hrs 24 minutes. In addition to our busy lives, exposure to artificial light (in particular the blue wavelengths of the visible spectrum, which constitute the predominant light output of the now ubiquitous computer screens and smartphones, has an incontrovertible and significant role in the worldwide epidemic of sleep deprivation.

Humans are not unique in their ability to sleep. All animal species studied so far possess this ability. Whilst most animal species display only one of the two known sleep phases, namely the non rapid eye movement (or NREM) type of sleep, birds and mammals experience both NREM and REM (or rapid eye movement) phases of sleep. It appears that REM sleep, which is the phase of sleep associated with dreaming, is most likely linked to the greater complexity of the avian and mammalian brains. 

A complete lack of sleep has been found to be incompatible with animal life and leads to the death of the organism over surprisingly short intervals of time. Laboratory animals have been shown to die as quickly of sleep deprivation as they do of food deprivation. Rats die in 9-10 days from total sleep deprivation and in about the same duration of exclusively REM sleep deprivation. They can live for slightly longer (about 21 days) without NREM sleep.

Sleep occurs through an interplay between two major hormones in our bodies, cortisol and melatonin (Fig 1). At dusk, progressively increasing amounts of melatonin are secreted from the pineal gland in the brain and circulated throughout the body signalling the onset of the next sleep cycle. Concomitantly cortisol levels fall. Melatonin levels peak around 1 a.m. at which time cortisol levels are at their lowest levels of the day. Thereafter there is a steady switch in the levels of two antagonistic hormones with cortisol levels increasing to peak at dawn while melatonin levels decline. Individuals with insomnia, especially those of older age, are likely to produce lower levels of melatonin and / or higher levels of cortisol.

Wakefulness and it’s accompanying metabolic demands result in the inevitable production of toxic by products which in turn create oxidative stress or low level damage across the whole body. Sleep may be considered as the price animals pay for wakefulness, as it is during this period of reduced metabolic demand that the body and brain set about repairing and restoring healthful function and setting into motion anabolic processes necessary for growth. In humans, sleep deprivation has been shown to increase the risk of all major diseases such as cancer, heart disease, metabolic disorder and obesity, neurodegeneration as well as psychiatric disorders. 

Men who sleep less than 7 hours per day are likely to have testosterone levels comparable to men 10 years their senior. Lack of sleep also adversely influences male fertility by directly decreasing sperm count and motility and making it more likely that the sperm will contain genetic aberrations. Similarly suboptimal reproductive function (in the form of a higher incidence of menstrual irregularities) has been shown to be linked to sleep deprivation in women. 

Sleep also has a profound influence on cognitive function, memory and mood. After learning, sleep is essential for consolidation of memories whereby the short term memories stored within the hippocampal region are moved to their more long term storage within the neuronal networks of the prefrontal cortex. This happens during the deeper stages of NREM (Non Rapid Eye Movement) sleep. This transferral of memory files out of hippocampal storage is essential before the brain becomes ready to receive new information or learning. Therefore sleep is vital both for the consolidation of newly acquired memories and to prepare the brain for new or further learning. A study on young, healthy adults who were made to forego sleep for one night and then asked to perform learning tasks which required memorizing the following day, whilst inside an FMRI (Functional Magnetic Resonance Imaging) scanner, revealed a 40% reduction in brain activity in the hippocampus compared to similarly aged individuals who had had adequate sleep the night before. 

A strong and most likely causal link has also emerged between sleep deprivation and dementia. It is known that the quantity and quality of sleep deteriorates with increasing age. On average, healthy adults spend about 25% of their total sleep duration in the deepest phases of NREM sleep, which is the period when the brain carries out most of it’s housekeeping and reparative work. This fraction of sleep is most likely to be impaired in older individuals. In short term sleep studies conducted on mice, animals deprived of NREM sleep for 7-10 days showed higher levels of beta amyloid protein which is associated with the occurence and development of Alzheimer’s disease.

The mechanism by which sleep helps maintain the health of brain cells (neurons) has been elucidated in recent years. Whilst medical science has long been aware that our body has a lymphatic network (which can be likened to a sewage system responsible for transporting and clearing toxic waste products of cellular metabolism from the spaces between cells), it has only recently emerged that a similar system exists in our brains. The Glymphatic system, named after the glial cells which support neuronal function, plays a similar role in the clearance of toxic byproducts of metabolism and misfolded proteins which accumulate in the spaces between brain cells or neurons. Such debris, if left uncleared, impairs electrical conductivity between neurons. During the deeper stages of NREM sleep, the glial cells shrink in volume by upto 60% allowing cerebrospinal fluid to percolate through the temporarily wider intercellular spaces, clearing debris and improving the transmission of impulses across synapses.

There is now a robust body of evidence to show that sleep deprivation even affects the expression of genes, hundreds of them throughout our bodies. Roughly half of the affected genes show increased expression of the proteins they code for, whilst the remainder show a decrease in expression. Of note is the observation that reduced gene expression affects mostly genes regulating immune function, metabolism and reproductive function. Conversely increased expression affects genes mostly involved in chronic inflammation and dysregulation of appetite. 

In a short study (lasting a week) where the subjects were limited to a maximum of 4 hours of sleep per night, a shocking reduction (about 70%) in the numbers of natural killer cells was observed. Natural killer cells are a valuable component of our innate immune system and their chief role is immune surveillance against invading pathogens and rogue cells which have developed the potential to form tumours.

Furthermore, sleep is the cheapest and most effective blood pressure medication which allows our arteries the time to relax and repair their lining. When the extent of damage to the endothelial lining of arterial walls exceeds the bodies capacity to repair it, atherosclerosis ensues.

Four components of good sleep are it’s regularity, continuity (lack of fragmentation), duration (of total sleep and the relative length of each stage) and finally quality (which is measured by it’s electrical signature). The brain’s electrical activity during sleep can be measured by a device called a Polysomnogram and shows distinct patterns during the different phases. Recommendations for sleep optimization include maintaining a regular sleeping routine and restricting exposure to bright artificial light for a minimum of 1 hour before bedtime. Sleep quality has also been shown to be enhanced by total darkness in the sleep environment. Furthermore, sleep apnoea (or snoring) is a common sleep disorder which significantly impairs sleep efficiency. Effective treatments now exist for this condition. 

The brain has different appetites for the different phases of sleep at different times during the night. For instance between 9.00 p.m. and 3.00 a.m. it prefers NREM sleep whilst between 3.00 p.m. and midday (if sleep continues that long) it prefers REM sleep. It understandably then follows that delaying sleep onset can mean that the individual has a disproportionate NREM deficit while still maintaining adequate REM sleep.

Sleep is mother nature’s most democratic and effective health insurance which allows us the opportunity to repair our bodies and mitigate the damage inflicted by our lifestyle choices. Therefore, the responsibility falls squarely upon us humans to maximize the benefit we derive from our bodies best attempt at disease prevention and longevity.