The Science of Sleep
Most people spend nearly one-third of their lives sleeping, so it is not surprising that sleep plays an important role in shaping our quality of life. A poor night’s sleep often means a grumpy you in the morning–a quality that can rub off on the people around you, making them grumpy in turn. It can mean you will be less productive at work, or less attentive during class. A poor night’s sleep can increase stress levels, which leads to worse sleep, which leads to more stress and so on.
The modern era’s 24/7 society has had a large impact on how we sleep, with increased light pollution, electronic screen time, stress, and reduced physical activity being a few of the factors affecting sleep. The Centers for Disease Control and Prevention (CDC) in the United States considers insufficient sleep to be a significant public health problem. In this article, I want to identify a few of the determinants of sleep quality, and how they affect a person’s quality of life.
Why Sleep Matters
- Productivity Loss: Insomnia or insufficient sleep has been shown to cause reduced workplace productivity and performance. Insomnia can cause significant impairments to attention, decision-making, memory, and motivation (1).
- Economic Costs: Productivity loss naturally leads to economic loss. A study of 4188 employees at 4 US corporations found that “the associated annual economic costs due to lost productivity for the entire work population at the participating companies were estimated to be $54 million ($1967/employee).” (1). A 2004 study out of the United States claims that insufficient sleep affects 70 million American citizens and has annual costs of $15 billion in health care expenses and $50 billion in lost productivity (2). A separate study examined the costs of sleep-related accidents, finding that in 1988, the total cost of accidents related to sleepiness was between $43.15 billion and $56.02 billion in the United States (3). Costs have likely gone up a fair amount since then.
- Safety: Insufficient sleep can increase the risk of motor vehicle and other types of accidents, largely due to reduced attention and awareness levels. Nobody wants a sleep-deprived pilot flying their plane.
- Quality of Life: A better sleep means a more restful you. A more restful you means you will be less stressed and have better moods. Everyone knows someone who is a bear in the morning; don’t be that person.
Determinants of Sleep Quality
- Stress: It should come as no surprise that stressors are a significant determinant of sleep problems. Studies in Japan and Europe, as well as the US have found associations between psychosocial stress and poor sleep quality. For example, it was found that in Japan, “lower control at work, higher work demands, lower social support, shorter and longer working hours, shift work, being single, higher family-to-work conflict, and higher work-to-family conflict were independently associated with poorer sleep quality in both men and women.” (4).
- Exercise: Everyone knows exercise is good for you, and its effects on improving sleep quality can be included on the list of reasons why. In a study of middle-aged adults with sleep problems, it was found that “regular aerobic or resistance exercise training significantly improves sleep quality in adults over 40 years of age. Those who exercised had a reduced time taken to fall asleep after going to bed and reduced medication use for insomnia.” (5). Furthermore, conditions such as adult-onset diabetes and obesity, which can be prevented with exercise, are known to reduce sleep quality and can cause sleep apnea.
- Screen Time: A relatively new factor in today’s age of technology, many people are on their tablets or smartphones before bedtime. A literature review of 67 studies found that in children and adolescents, “there is a significant association between screen time and reduced sleep duration and increased sleep problems, across a range of screen types and sleep outcomes in 90% of the studies.” (6).
Looking at the Numbers
I’m going to list some numbers from a cross-country study of over 62,000 people looking at sleep factors (7). I recommend checking out the study for yourself at https://www.rand.org/pubs/research_reports/RR1791.html. Try going through the following to see which factors apply to you and see how many hours of sleep you are losing per day.
- Exercise regularly and watch your weight:
- Persons with above-normal BMIs sleep 2.5 to 7min less per day.
- Individuals with less than 120min of physical activity per week sleep 2.6min less per day.
- People consuming more than two sugary drinks per day sleep 3.4min less per day.
- Managing mental wellness:
- Individuals with mental health problems sleep 17.2min less per day on average.
- Men sleep 9min less per day compared to women.
- Don’t smoke:
- Smokers sleep 5min less per day.
- Career-related stress:
- Individuals with financial concerns sleep 10min less per day.
- People with no control over their work routine sleep 2.3min less per day.
- Having a 30-60 minute one-way commute means sleeping 9.2min less per day, and a 60+ minute commute means 16.5min less.
- Individuals with unrealistic workplace time pressures sleep 8min less per day.
- People working irregular hours, like nurses doing shift work, sleep 2.7min less per day.
- Family life:
- Unmarried people sleep 4.8min less per day, while separated or divorced people sleep 6.5min less.
- People with children living in the same household under 18 years old sleep 4.2min less per day.
- Persons providing unpaid care to family members, such as a daughter providing care to her sick father, sleep 5min less on average.
- Rosekind, M. R. et al. The Cost of Poor Sleep: Workplace Productivity Loss and Associated Costs. Journal of Occupational and Environmental Medicine 52, 91–98 (2010).
- Lamberg, L. Promoting Adequate Sleep Finds a Place on the Public Health Agenda. JAMA, 291, 2415–2417 (2004).
- Leger, D. The Cost of Sleep-Related Accidents: A Report for the National Commission on Sleep Disorders Research. Sleep 17, 84–93 (1994).
- Sekine, M., Chandola, T., Martikainen, P., Marmot, M. & Kagamimori, S. Work and Family Characteristics as Determinants of Socioeconomic and Sex Inequalities in Sleep: The Japanese Civil Servants Study. Sleep 29, 206–216 (2006).
- Yang, P.-Y., Ho, K.-H., Chen, H.-C. & Chien, M.-Y. Exercise training improves sleep quality in middle-aged and older adults with sleep problems: a systematic review. Journal of Physiotherapy 58, 157–163 (2012).
- Hale, L. & Guan, S. Screen time and sleep among school-aged children and adolescents: A systematic literature review. Sleep Medicine Reviews 21, 50–58 (2015).
- Hafner, Marco, Martin Stepanek, Jirka Taylor, Wendy M. Troxel, and Christian Van Stolk, Why sleep matters — the economic costs of insufficient sleep: A cross-country comparative analysis. Santa Monica, CA: RAND Corporation, 2016. https://www.rand.org/pubs/research_reports/RR1791.html