Newsletter #158: Sleep & Your Brain 🧠
Welcome to the latest humanOS newsletter! This week, we looked at the impact of sleep loss on brain health and cognitive performance. (Spoiler: it’s not great)
We learned that sleep deprivation is linked to greater risk of dementia, and we got some insight into the possible underlying mechanism. Furthermore, sleep loss negatively impacts our ability to focus and ignore distractions around us. Fortunately, moderate-intensity exercise appears to help offset this irritating effect.
To find out more, scroll down 👇🏼
This Week’s Research Highlights
🦠 Short sleep in midlife is associated with increased risk of late-onset dementia.
Researchers analyzed data on sleep duration and dementia incidence from 7959 participants in a large cohort study of British civil servants, who were followed for 25 years. They found that sleep duration of six hours or less during middle age was associated with higher risk of developing dementia, compared to those who got normal sleep. Persistent short sleep duration (six hours or less) was associated with a 30% increased risk of dementia, independent of sociodemographic, behavioral, cardiometabolic, and mental health factors.
🧠 Sleep deprivation impairs clearance of substances from the brain.
It has been hypothesized that one of the fundamental purposes of sleep is to clear out waste products from brain metabolism, and that a potential cause of some forms of dementia is a reduction in the clearance of these substances. In this study, researchers injected a tracer molecule into the cerebrospinal fluid of two groups of subjects: one group which underwent total sleep deprivation, while another age- and gender-matched control group was allowed to sleep freely. When the researchers examined brain imaging later, they found that the sleep deprivation group had a higher proportion of tracer lingering throughout their brains (suggesting that they were not eliminating substances from the central nervous system as efficiently). Interestingly, the sleep-deprived group still had more tracer in their system even after they were allowed a full night to catch up on their lost sleep. The researchers conclude: “The present results provide in vivo evidence that one night of total sleep deprivation impairs molecular clearance from the human brain, and that humans do not catch up on lost sleep.”
🎯 Poor sleep makes it harder to focus and shut out distractions.
Researchers recruited 23 people with chronic insomnia, as well as 23 people with normal sleep (controls). Participants slept in the lab overnight, then were administered a test of attention. The subjects were asked to focus on a circle of letters in the middle of a computer screen, and react as fast as possible to a target letter while ignoring other distracting letters that appeared on the screen. And indeed, the subjects with insomnia had a harder time focusing on the task and ignoring the distractions, compared to those who slept well. The researchers suggest that this is due to compromised cognitive control. Poor sleep makes it harder to accurately assess which stimuli we should be paying attention to, which means of course that we are more easily consumed by distractions than we otherwise would be. This has obvious implications for normal daytime functioning, like at work or school, but also for activities like driving, where even fleeting deviations in attention can be disastrous.
🏃♂️ Exercise may help offset the negative impact of sleep loss on cognition.
Okay, so we know that acute sleep deprivation is not great for brain performance (Most likely you already have personal experience with this phenomenon). But what can be done about it when you do experience a bad night of slumber? To explore this, researchers recruited twelve healthy students at Niigata University in Japan, and had them complete cognitive testing on different days under two different conditions: 1) well-rested and 2) 24-hour sleep deprivation. Subjects were administered a cognitive assessment when they arrived at the lab, and then did the tests again after a moderate-intensity exercise bout on a stationary cycle. Unsurprisingly, sleep deprivation resulted in significant declines in cognitive function. However, after the subjects exercised on the bike, this deterioration in performance was reversed, and the subjects also reported being less sleepy. How come? When the scientists measured oxygenation of the brain (via near-infrared spectroscopy), they found that the exercise had boosted oxygenation in the dorsolateral prefrontal cortex - a part of the brain that is key to executive function - which may have had a beneficial effect on cognition.
Podcasts We Loved This Week
- James Kirkland: Targeting senescent cells to reverse age-related diseases. Via STEM-Talk.
- Deirdre Tobias: Study design, diet collection methods, and nutritional epidemiology. Via Sigma Nutrition Radio.
- Angela Rasmussen: Is COVID-19 herd immunity even possible anymore? Via Science Friday.
Products We Are Enjoying
Blue Light Blocking Computer Glasses
These glasses are very inexpensive, come in lots of colors and styles, and are pretty much perfect if you have a job that involves looking at a computer screen at night. What makes them really useful is that they filter UV and some blue light, but they appear to be almost entirely clear, without any orange tint, so your vision isn’t distorted. Plus they don’t look weird, like some blue-blocker glasses tend to.
humanOS Catalog Feature of the Week
How-to Guide - Smart Daily Light
This week, we’d like to highlight our How-to Guide for Smart Daily Light. We evolved in the presence of natural daily cycles of light and darkness. But obviously, the invention of artificial lighting means that we can now fully control when and how much light we’re exposed to, which has altered this relationship. Today, most of us spend the majority of the day indoors, under comparatively dim artificial lights. Then, after sundown, we are exposed to more bright light, and importantly more blue light due to our digital devices. Consequently, we are getting less bright light during the day and less darkness at night.
This is important because light sends crucial signals to the body, and the intensity and timing of this light matters for your health as well as your performance. But fortunately, there is a lot you can do about it. In this guide, we discuss how you can achieve a pattern of natural light and darkness in the modern world by adjusting behavior, modifying your indoor spaces, configuring your devices, and more.
