For all its amenities, modern life is surprisingly difficult. A century ago, the primary challenges of living were physical; we worked in factories or on farms, and housework and meal preparation demanded hours of labor. After many millennia of existence defined by dawn-to-dusk physical demands, the burden of modern living has been lightened by vehicles, automated devices, broadband internet, and same-day delivery services. Citizens from the 1920’s, however, would likely be disappointed to learn that a century of unparalleled technological progress has largely exchanged lives dominated by physical stressors with lives dominated by emotional and social stressors.
It is difficult to argue that we are happier than a century ago and—despite having longer lifespans boosted by clean water and antibiotics—in most ways less healthy. The same technological forces that shaped modern times have offered many remedies to 21st century ailments. We have activity trackers to inspire exercise, social media to assuage loneliness, diet books and internet health gurus to guide our nutrition, and a dizzying number of entertainment options in the form of television channels and video games.
Yet for all these breakthrough gadgets and expensive technologies, arguably the most effective balm for modern living is sleep. No medicine, supplement, or psychotherapy provides even a fraction of the benefits conferred by sleep to our minds, bodies, and spirits. While a profit-hungry industry strives to create market demand for sleep products, the wise consumer appreciates that healthy sleep is overwhelmingly the product of cost-free habits and lifestyle practices rather than equipment or pharmaceuticals.
We know what works: regular sleep and wake routines; morning sunlight to optimize circadian hormones; regular exercise to generate physical fatigue and ameliorate stress; meditation and relaxation for calming the mind; cool and dark bedrooms to facilitate restful slumber; and consistent CPAP use for those with sleep apnea. For the typical person, their sleep can be dramatically improved by the practice of these latter strategies without lightening their wallet. Recent science further demonstrates the diverse ways that sleep improves our well-being. The range may surprise you; virtually no area of physical or mental health is exempt from the effects of sleep.
A summary of sleep science
1. Sleep and pain sensitivity: Even a single night of poor sleep reduces our pain threshold. A study by Matt Walker’s team at UC Berkeley showed that, compared to brain function after a full night’s sleep, pain-related areas of the brain were 42 percent more sensitive to pain stimuli induced by laboratory tests. For context’s sake, a 42 percent difference in pain sensitivity is larger than the effect of many pain medicines.
2. Sleep and alcohol: The relationship between sleep and alcohol use is complex. On one hand, small amounts of alcohol show short-term benefits in helping some people initiate sleep (this benefit wears off, however, for most people within a few days). In contrast, any benefit from falling asleep faster may be nullified by the suppression of REM sleep caused by alcohol. The alcohol-REM suppression effect appears to be dose-related. For example, REM sleep may rebound to higher than normal levels in the second half (i.e., catching up on lost REM) of the night after smaller doses of alcohol have been metabolized. In the case of higher doses of alcohol, however, REM suppression may occur throughout the night as is often seen in persons with alcohol dependence.
3. Sleep and caffeine: With an estimated 90 percent of Americans reporting daily caffeine intake, it is important to understand the effects of caffeine on sleep and health. Research shows that caffeine has an average half-life (the time needed to metabolize 50 percent of the drug) of approximately five hours. However, due to differences in drug metabolism between people, this can range from one and a half to nine and a half hours! In real-life circumstances, this means that the average person consuming a cup of coffee at noon (about 100 mg of caffeine) would still have about 50 mg of caffeine in their body at 5 p.m. and 25 mg at 10 p.m. These results, however, would vary markedly for slower caffeine metabolizers, who might still have a high percentage of caffeine affecting their body in the evening. For these reasons, many researchers encourage stopping caffeine use at least six hours before bedtime.
4. Sleep and vaccine response: In a world dominated by pandemic news and recommendations to vaccinate, a curiously overlooked fact is the importance of vaccinating in a well-rested state. Quality sleep profoundly affects the ability of our immune system to mount a favorable response to vaccination. For example, in one of several studies measuring immune system response to flu vaccines, a group of healthy participants restricted to four hours of sleep for six nights showed less than half the number of antibodies ten days after vaccination. Expressed reversely, this implies that receiving a vaccination in a well-rested state could double its effectiveness.
5. Sleep and learning: Practice does not make perfect. More accurately stated, it is practice—coupled with quality sleep—that enables learning and improvement. In a 2002 study of participants assigned to a motor learning task combined with differing sleep-wake patterns, participants obtaining a regular night’s sleep after learning showed a 20 percent improvement in the task the next day. In contrast, participants staying awake for the same period showed no improvement. Interestingly, more than 50 percent of the improvement could be explained by the amount of stage 2 non-REM sleep that is typically obtained early in the night.
6. Sleep and dementia: Because the brain is an energy-intensive organ, it produces a lot of metabolic waste products. Sleep serves a vital restorative function by facilitating the removal of the waste products accumulated in the brain during the day. Without sleep, this cleaning process does not occur, with potential long-term implications for dementia. For example, in a 2018 cross-over study assigning participants to a normal sleep versus a single night of sleep deprivation, the latter condition was associated with significantly reduced clearance of β-amyloid, a plaque associated with risk of Alzheimer’s Disease.
7. Sleep and hormones: One of the primary roles of sleep is hormone regulation. Optimizing sleep improves the function of appetite hormones such as leptin and ghrelin as well as sex hormones such as testosterone. Even in young men, sleep loss rapidly disrupts hormone function. In a study restricting sleep to five hours per night for one week in a group of healthy men in their 20’s, daytime testosterone levels were lowered by 10-15 percent and accompanied by large self-reported decreases in vigor.
8. Sleep and healing: Whether you are an athlete recovering from training or a patient recovering from surgery, sleep is critical for your body to heal. In addition to the above hormonal and immune system effects of sleep, sleep is also the period of peak protein synthesis. Protein synthesis is the process of creating new proteins and is an essential part of repairing damaged tissues and creating new cells. A 2021 study recruiting healthy young adults found that a single night of sleep deprivation decreased protein synthesis by 18 percent, along with a 21 percent increase in cortisol and 24 percent decrease in testosterone.
9. Sleep and heart rate variability: Heart rate variability (HRV) refers to beat-to-beat variability between heartbeats. Counterintuitively, greater HRV is healthy, representing a dynamic heart capable of responding effectively to internal and external demands. Low HRV is associated with poorer metabolic function and increased risk of cardiovascular events. Improving the quality and quantity of our sleep is one established way to maintaining higher levels of HRV and it is never too young to start. Even in children and young adults, for example, research shows that impaired sleep is associated with reduced HRV.
10. Sleep and insulin sensitivity: Even partial sleep deprivation has rapid adverse effects on insulin sensitivity. For example, in a crossover study of participants with type 1 diabetes obtaining full and four-hour sleep intervals, insulin sensitivity was reduced by more than 20 percent following the night of partial sleep deprivation. Many other studies with type 2 diabetes and even metabolically normal participants show similar results. For comparison's sake, the improvement in insulin resistance achieved by healthy sleep is as large or larger than established diabetes medicines such as metformin.
