A recent study suggests a lack of sleep costs the United States economy $411 billion dollars each year due to lower productivity levels (Hafner et al. 2017). According to a recent Gallup poll, 40% of Americans rarely get more than six hours of sleep per night (Murphy 2018). Many people know a bad night of sleep results in poorer concentration the next day, but the health and broader cognitive effects of chronic sleep deprivation often go undiscussed. Western University in Canada recently conducted a large study investigating sleep’s impact on cognitive functioning in adults. The results were shocking; researchers found sleeping less than four hours per night on a typical basis was equivalent to adding eight years to one’s age – a huge cognitive decline. In a busy society where productivity is often valued over sleep, it is crucial to understand sleep’s importance for the brain (Aloia 2017).
In 2017, neuroscientists from the Brain and Mind Institute at Western University in Canada conducted the world’s largest sleep study to date with 16,812 participants. Previous research focused on older adults and did not study chronic sleep deprivation; researchers in this 2017 study hoped to fill this gap and understand the cognitive impact of sleep deprivation. Cognitive abilities include skills such as inhibition, selective attention, reasoning, verbal short-term memory, spatial working memory, planning, and cognitive flexibility. Brain and Mind Institute researchers wanted to understand which cognitive abilities sleep deprivation affects, the optimal amount of sleep for prime cognitive functioning, and how sleep needs vary by age. It was hypothesized there would be an inverted U-shaped relationship between sleep duration and cognitive functioning, with subjects who chronically underslept or overslept exhibiting poorer cognition across all domains. Scientists also theorized lack of sleep would have a larger impact on older adults’ cognitive functioning.
Scientists used the CBS online platform, and social media platforms Facebook and Twitter to recruit worldwide adult study participants. Volunteers completed an online questionnaire with basic information about their age, education, and mental health history as well as the number of hours slept per night on average in the past month, and their bedtime and wake-up time the day of the study. After completing the questionnaire, participants took 12 randomly ordered cognitive functioning tests, such as the Interlocking Polygons, Token Search, Grammatical Reasoning, and Feature Match – all of which investigated different types of memory and functioning. Scientists were able to use the data from the 12 tests to assign each participant four composite scores for each of the three specific domains – short-term memory, reasoning, and verbal ability. Study results were published in the SLEEP journal in 2018.
Overall, there were statistically significant relationships between self-reported typical number of hours slept per night and the reasoning, verbal, and overall composite scores. Scientists found sleep duration does not appear to impact short-term memory. These results suggest sleep patterns only influence higher-level cognitive processes – reasoning and verbal functioning. Seven to eight hours was found to be the optimal amount of sleep per night, and an inverted U-shaped association between performance and sleep duration was seen. Even a single night of poor sleep has a significant impact on functioning, showing that “sleep debt” impairs cognition even after just one night. The optimal amount of sleep does not appear to differ by age for adults, which went against scientists’ original hypothesis.
This SLEEP journal study investigated an important societal topic and was ethically conducted. Participants did not receive compensation and funding was by an impartial source – Cambridge Brain Sciences – whose goal was to understand how sleep affects cognition. Although the study was repeatable and ethical, there are flaws that should be addressed in a future study. This study primarily recruited participants through CBS online, which may have favored certain types of people and only allows for participants who have computer and internet access. Sleep patterns were self-reported which may bring in a lot of bias since some people may exaggerate or have poor estimates of their sleep patterns. Additionally, only sleep duration was investigated, when it is known that sleep quality also plays a major role in functioning. Utilizing sleep-tracking devices that also give a sleep score, such as the Fitbit, in the month leading up to the test, could reduce self-reported bias while also accounting for sleep quality, not just duration. If this study were to be redone, I believe participants should be selected from multiple viewer bases, and computers, Wi-Fi, and sleep tracking devices should be provided.
Overall, this study provided information that is crucial to a society where sleep is under-valued. Hopefully, this information can change the sleep patterns of sleep-deprived employees or students, especially those whose functioning is necessary for safety. This article illustrates that even one night of poor sleep negatively affects performance, and multiple nights of ‘recovery sleep’ cannot erase overall sleep patterns. A consistent seven to eight hours of sleep per night is crucial for optimal functioning, showing that staying up late cramming for an exam, frequent night-shift work, and early school start times should be reevaluated.
Not only is sleep critical for cognitive functioning, it also plays a major role in our health. A recent study suggests participants who often slept less than seven hours per night were more likely to experience head or chest colds (Prather and Leung 2016). Other short-term consequences of sleep deprivation or disruption include increased stress responsivity, mood disorders, and muscle and tissue pain. Long-term consequences include elevated risk of hypertension, type II diabetes, cardiovascular disease, and colorectal cancer (Medic et al. 2017).
As a society, there needs to be a shift towards prioritizing sleep for our health and cognitive functioning. Companies and schools need to advocate for sleep, healthcare providers need to discuss sleep when treating patients, and heavy machinery or transport employers need to ensure their employees slept enough before working. There are still many unknowns about sleep’s impact on the body, but what we do know should have us ensuring we get seven to eight hours of shuteye per night.
References
Main Article:
Wild C, Nichols E, Battista M, Stojanoski B, Owen A. 2018. Dissociable effects of self-reported daily sleep duration on high-level cognitive abilities. SLEEP. [accessed 2021 February 5]; 41(12): zsy182. https://pubmed.ncbi.nlm.nih.gov/30212878/. doi:10.1093/sleep/zsy182.
Supporting Articles:
Aloia, M. 2017. A society without sleep. Huffington Post; [accessed 2021 Feb 10]. https://www.huffpost.com/entry/a-society-without-sleep_b_9470680.
Hafner M, Stepanek M, Taylor J, Troxel WM, van Stolk C. 2017. Why sleep matters- the economic costs of insufficient sleep: a cross-country comparative analysis. Rand Health Q. [accessed 2021 Feb 17]; 6(4):11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627640/. doi:10.1093/sleepj/zsx050.802.
Medic G, Wille M, Hemels M. 2017. Short- and long-term health consequences of sleep disruption. Nature and Science of Sleep. [accessed 2021 Jan 31];. 9:151-161. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5449130/. doi:10.2147/NSS.S134864.
Murphy B. 2018. It’s official: A massive sleep study of 44,000 people shows exactly how much sleep you need each night. Inc; [accessed 2021 Feb 17]. https://www.inc.com/bill-murphy-jr/its-official-a-massive-sleep-study-of-44000-people-shows-exact-amount-of-sleep-you-need-each-night.html
Prather A, Leung C. 2016. Association of insufficient sleep with respiratory infection among adults in the United States. JAMA Internal Medicine. [accessed 2021 Jan 31]; 176(6): 850-2. https://pubmed.ncbi.nlm.nih.gov/27064773/. doi:10.1001/jamainternmed.2016.0787.
Featured Image:
Google Images, Creative Commons license.