Newsletter #310: Physical Activity, Sleep Quality, & Your Brain
Most of us are all too aware that sleep affects our mood, as well as our cognitive functions. Lab trials of sleep restriction, as well as sleep extension, bear this out.
Similarly, acute physical activity can boost mood, and quell both psychological and physiological responses to stress. Indeed, it has been suggested that exercise is the most effective mood-regulating behavior at our disposal.
The mechanisms and pathways through which sleep and physical activity influence mood and cognitive performance remain to be fully elucidated. This is perhaps, in part, because aspects of the mind are notoriously hard to study rigorously. But we also need to appreciate that the pillars of lifestyle do not influence aspects of our health in isolation. They work together in complex ways.
For example, it is well established that exercise affects sleep. Controlled laboratory studies have shown that physical activity can accelerate sleep onset and modestly increase total sleep duration. But exercise can also affect sleep architecture, and this may be even more critical with respect to mood and cognition than the amount of sleep that you get.
Sleep architecture, as the name suggests, is the fundamental structural organization of sleep. It is traditionally broken into two main stages: rapid-eye-movement (REM) sleep and non-rapid-eye-movement (NREM) sleep. NREM sleep is further subdivided into three phases, each of which represents increasing depth of sleep.
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From: https://www.ncbi.nlm.nih.gov/books/NBK19956/
When you sleep, you alternate between NREM and REM in a cyclic fashion, and an array of characteristic physiological changes occur within each stage, which enable the brain to recuperate from stressors and consolidate new memories. Consequently, you’d expect problems to emerge when these delicate cycles are disrupted. And sure enough, irregularities in sleep architecture are associated with various psychological and neurological disorders. Notably, depressive symptoms are frequently accompanied by shifts in the timing and relative length of REM and NREM.
So, you might be able to see where this is going. Could physical activity enhance mood and well-being through its effects on sleep?
For the first time, a new study directly examines this question.
This Week’s Research Highlight
Physical activity affects REM sleep timing and duration, which in turn boosts energy and alleviates stress.
Researchers in Austin recruited 82 undergraduate students at the University of Texas, and equipped them with Fitbits to measure both physical activity and sleep. Importantly, the model they were using, the Inspire HR, is capable of capturing not just how long users sleep, but also time spent in each sleep stage (albeit not quite as accurately as polysomnography). In this way, the research team could collect data from a relatively large sample in a natural setting (as opposed to a sleep lab), and over a much longer timespan than if they were relying upon polysomnography.
Additionally, participants were instructed to use a smartphone app twice per day to record their self-assessment of the previous night's sleep, and rate their current psychological state on five different dimensions: contentment, stress, loneliness, sadness, and energy.
Over the course of several months, the researchers were able to acquire objective data on sleep and physical activity, and then analyze how each of these interacted with one another and correlated with the psychological states of their participants.
First, let's examine how physical activity affected sleep in these participants.
Physical activity was linked to a higher ratio of NREM sleep to REM sleep, as well as increased REM latency. REM latency refers to how long it takes a person to reach their first REM sleep stage. We'll get into the significance of this finding shortly.
We have known for some time that acute exercise tends to delay REM onset and reduces the total amount of REM sleep. For instance, marathon runners experience a decrease in REM sleep as well as prolonged REM latency.
Why? Well, decreased REM could be reflective of a consolidation in REM, as well as an increased demand for NREM sleep by the body. Exercise tends to amplify the deepest stage of NREM sleep, also known as slow wave sleep (due to how the electrical activity appears on an electroencephalogram). Slow wave sleep is a uniquely restorative state, critical for the processes of learning and memory storage, as well as tissue repair and muscle remodeling.
So, exercise promotes increased NREM sleep to recover from metabolic stress, and this seems to indirectly lead to delayed and reduced REM sleep.
Next, let's take a look at how these alterations in sleep architecture influenced the mental states of these participants.
The sleep architecture changes described above (longer REM sleep latency, lower ratio of REM to NREM) were in turn linked to positive mood, increased energy, and reduced stress.
How come? To understand how these subtle differences in sleep quality could have psychological effects, I think looking at individuals with the most serious mood impairments may be instructive here. It has been known for decades that REM latency is chronically shortened in depression, and depressed individuals tend to spend more time in REM relative to other stages. In fact, this sleep architecture profile is arguably the only true biomarker of major depression that we have found.
Even more intriguing, reductions in REM sleep and increased REM latency are frequently observed in response to antidepressant medications in both depressed and non-depressed individuals, suggesting a potential causal relationship. Experts have proposed that changes in sleep staging are a key mechanism through which these treatments improve mood. In other words, physical activity seems to shift sleep architecture in a manner that mirrors the effects of antidepressants. And this is likely beneficial not just in clinical populations, but for the rest of us.
Random Trivia & Weird News
A recently discovered group of fungicidal compounds was named for Keanu Reeves — on account of their remarkable lethality.
Many fungi that are pathogenic to humans are becoming resistant to antifungal drugs. To that end, scientists have been busily pursuing novel substances that can fight such infections.
Last year, researchers at the Hans Knöll Institute isolated a group of antimicrobial compounds from Pseudomonas, which the bacterium manufactures as a defense against amoebas. They tested the compounds against flowers infected with fungi, and were so impressed with the results that they named the new chemicals after the actor, ostensibly for his roles in John Wick and The Matrix.
As the authors state in their paper characterizing the compounds: “In fact, the new NRLPs are so efficient at killing different microbial species that we named them keanumycins in tribute to the actor Keanu Reeves, who played many iconic killers in his cinematic career.”
Podcasts We Loved This Week
- David Raubenheimer & Jonathan Sholl: Nutritional geometry, philosophy of science & a case for reductionism. Via Sigma Nutrition Radio.
- Sammy Ramsey & Madison Sankovitz: Inside the race to save honeybees from parasitic mites. Via Science Friday.
Products We Like
Manta Sleep Mask
Sleep masks can not only help you fall asleep in environments polluted with ambient light, but they can also enhance sleep quality, which in turn can boost learning and alertness the next day.
Despite being aware of the potential benefits,, I’ve struggled in the past to stick to using sleep masks as part of my normal bedtime routine. I don’t really like the feeling of fabric pressing on my eyelids, and masks often shifted around while I was sleeping, even coming off entirely.
That’s why Manta was a revelation for me. These masks have adjustable eye cups that mold to your face, blocking out light no matter how bright your surroundings. The cups are also deep enough for you to open and blink your eyes, meaning no pressure on the lids.
humanOS Catalog Feature of the Week
Body Timing and Health
In this course, Dan goes over the evolution and physiological purpose of biological rhythms, as well as how they are regulated in response to environmental stimuli. Then, he delves into how these biological clocks influence both acute performance and long-term health, and what happens when they get out of sync.
Finally, all of this juicy info is synthesized into practical applications — what you can do right now to align your circadian rhythms, to keep your mind and body working at their very best.
Wishing you the best,
