First let me start out by giving credit where credit is due. The majority of the information in this post has been inspired by Matt Walker, a professor and neuroscientist who focuses on the effect of sleep on health. Here is his website: https://www.sleepdiplomat.com/, and here is the TED talk where I first learned of him: TED talk. I found the information so fascinating and important that I felt the need to summarize it and pass it along. So here it goes:

Humans are the only animal on the planet that intentionally deprive themselves of sleep. Increasingly, our demands of work and the stigma of laziness for those who sleep in, have led to an overall decrease in total sleep across the population in industrialized countries. Our bodies are not equipped to deal with a lack of sleep and a cascade of negative events occur without rest. Lack of sleep can disrupt both mind and body and the consequences can be devastating.

Sleep deprivation affects the endocrine system, cardiovascular system, immune system, and even your DNA. Lack of sleep has a direct effect on testosterone levels and in one study, men who routinely slept 4-5 hours a night had testosterone levels of someone 10 years older. In other words, lack of sleep will age a man by 10 years. The same deficits are found in female reproductive health. Additionally, sleep deprivation leads to increased cortisol levels. Cortisol is correlated with stress and weight gain.

Cortisol has a negative effect on the cardiovascular system as well. Twice a year, 1.6 million unknowingly partake in an epidemiological study; daylight saving time. In the spring, when we lose an hour of sleep, there is a 24% increase in heart attacks the following day. Conversely, in the fall when we gain an hour, we see a 21% decrease in heart attacks the next day.

Perhaps the scariest effects of sleep deprivation are on the immune system, particularly on the natural killer cells. These are rapid response cells that kill virus-infected cells and tumor forming cells. Sleep deprivation inhibits these potent cells and In one study, just one night of 4 hours of sleep reduced natural killer cell activity by 70%. In fact, the link between sleep deprivation and cancer has become so clear that the World Health Organization has called nighttime shift work a probable carcinogen.

DNA and genes are also not protected from the consequences of lack of sleep. In a study where subjects were limited to 6 hours of sleep for a night, there were changes in DNA activity. Some genes were upregulated and some were downregulated. Genes associated with immune function were downregulated. Unfortunately, the genes that promote tumors, inflammation, and are associated with stress and cardiovascular disease, were all upregulated. There appears to be no system of the body that is not negatively affected by sleep deprivation.

There are well documented deficits that occur in the brain as well. Both learning and memory are impacted. Sleep appears to prime the brain for absorbing new information. The deeper states of sleep are where new memories are consolidated into long term memories, so in a sense, a good night of sleep is like hitting the save button on new information learned. The hippocampus is a region of the brain that functions to consolidate new memories. In MRI studies where subjects were sleep deprived, there was no activity of the hippocampus when the subjects were trying to learn something new.

As we age, memory and cognition decline, and occurrence of Alzheimer’s and dementia increase. It is also well known that as we get older, the quality and quantity of sleep declines. There is now evidence that this is not coincidental, rather they are interrelated. We already know that the lack of quality sleep from sleep apnea is related to dementia. We have a lymphatic system which is responsible for transporting fluids in the body like a septic system. We have discovered that there is an analogous system in the brain called the ‘glymphatic system’. It is largely disengaged during wakeful hours, and requires the deep stages of sleep to be activated. In particular, it removes build up of β-amyloid protein that has been linked to dementia.

So what do we do with this information outside of try to get more rest? If you have difficulty sleeping, let’s start with what not to do. Sleeping pills should be avoided as they don’t allow for quality sleep. They are more like being knocked out by a baseball bat. The habit of alcohol in the evening and caffeine in the morning can severely disrupt your sleep cycle. Artificial light inhibits sleepiness, so that means no staring at devices before bed. Also, the mind is highly associative, so if you are awake for too long in your bed, your brain will associate your bed with wakefulness. Change rooms if you are having difficulty sleeping.

There are things you can do to improve your ability to fall asleep and improve the quality of sleep. Matt Walker says that ‘regularity is king’. This means going to bed and getting up at the same time are crucial. Even on the weekend. Also temperature is important and sleeping temperature is surprisingly lower than you may guess. 65 degrees is the recommendation. The body has to decrease the core temp by 2-3 degrees to fall asleep and stay asleep.

Considering that sleep deprivation has such devastating consequences, and proper sleep has such considerable benefits, it should be a high priority. For students, pulling the all-nighter should be the exact opposite of what you should do. For working individuals, keep it regular, keep it cold, and keep it a priority. How much sleep? The National Sleep Foundation updated their recommendations in 2015:

• Newborns (0-3 months): Sleep range narrowed to 14-17 hours each day (previously it was 12-18)

• Infants (4-11 months): Sleep range widened two hours to 12-15 hours (previously it was 14-15)

• Toddlers (1-2 years): Sleep range widened by one hour to 11-14 hours (previously it was 12-14)

• Preschoolers (3-5): Sleep range widened by one hour to 10-13 hours (previously it was 11-13)

• School age children (6-13): Sleep range widened by one hour to 9-11 hours (previously it was 10-11)

• Teenagers (14-17): Sleep range widened by one hour to 8-10 hours (previously it was 8.5-9.5)

• Younger adults (18-25): Sleep range is 7-9 hours (new age category)

• Adults (26-64): Sleep range did not change and remains 7-9 hours

• Older adults (65+): Sleep range is 7-8 hours (new age category)

References:

Jessen, N. A., Munk, A. S. F., Lundgaard, I., & Nedergaard, M. (2015, December). The Glymphatic System: A Beginner's Guide. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4636982/.

National Sleep Foundation Recommends New Sleep Times. (n.d.). Retrieved from https://www.sleepfoundation.org/press-release/national-sleep-foundation-recommends-new-sleep-times.

Sleep Loss Results in an Elevation of Cortisol Levels the Next Evening. (1997). Sleep. doi: 10.1093/sleep/20.10.865

Walker, M. (n.d.). Matt Walker. Retrieved from https://www.ted.com/speakers/matthew_walker.

Whitworth, J. A., Williamson, P. M., Mangos, G., & Kelly, J. J. (2005). Cardiovascular consequences of cortisol excess. Vascular Health and Risk Management, 1(4), 291–299. doi: 10.2147/vhrm.2005.1.4.291